Dose-response relationships between energy availability and bone turnover in young exercising women

Pre-Season Energy Deficiency Predicts Poorer Performance During a Competitive Season in Collegiate Female Long-Distance Runners

Female distance runners are at a high risk for chronic energy deficiency (ED). ED during predominantly high-volume and/or high-intensity training phases may compromise performance. The relationship between pre-season energy status and running performance in female runners across a season is unclear. To test if energy status as defined by resting metabolic rate ratio (RMRratio) is associated with running performance, female collegiate distance runners (18-25 yr; n = 38) were assessed across 10-12 wks. Energy status, body composition, and 5 km time trial (measure of performance) were assessed pre- and post-competitive season. Runners were categorized at baseline based on pre-season measured-to-Cunningham1991-predicted RMRratio: metabolically suppressed (SUP: RMRratio < 0.92, n = 12) and energy replete (NSUP: RMRratio ≥ 0.92, n = 26). Repeated measures ANOVA tested effects of pre-season RMRratio groups, time, and group*time on performance. Linear regression analysis tested whether factors (body composition or total triiodothyronine, TT3) predicted performance across the season. Twenty-one runners (19.6 ± 0.2 yr, 20.2 ± 0.4 kg/m2) completed pre- and post-season performance runs. Groups had similar body mass, body mass index, percent body fat, and lean body mass. ANOVA revealed a significant group effect of RMRratio on running performance, but no effect of time or group*time. SUP had slower 5 km time trial performance compared to NSUP (22.4 vs. 20.4 min, p = 0.04). Controlling for post-season VO2max, pre-season TT3 predicted post-season 5 km times (R2 = 0.614, p = 0.001). Pre-season energy deficient female runners exhibited poorer running performance during a collegiate competitive season compared to pre-season energy replete runners. Early detection of metabolic compensation in runners may be necessary for optimal performance across a competitive season.

Diet, risk of disordered eating and running-related injury in adult distance runners: A systematic review and meta-analysis of prospective cohort studies

OBJECTIVES

To determine whether diet and disordered eating risk contribute to running-related injury risk in adult (≥18 years) distance runners.

DESIGN

Systematic review and meta-analysis.

METHODS

Random effects meta-analyses of prospective cohort studies compared dietary intake and disordered eating risk in distance runners with and without running-related injury. Quality of evidence was assessed using an adapted Grading of Recommendations Assessment, Development and Evaluation approach.

RESULTS

Fifteen studies (n = 5942 runners, 2364 female) were included, with nine studies in the meta-analyses. Sex differences were observed for total energy and total fat intake (both p = 0.01). Moderate certainty evidence indicated injured female runners had lower energy and fat intake than uninjured runners (mean difference [95 % confidence interval] = -449 kcal/day [-696, -202] and -20 g/day [-31, -9], respectively, both p < 0.001). Moderate certainty evidence suggested injured runners (combined sexes) had lower dietary fibre intake compared to uninjured runners (-3 g/day [-5, -0], p = 0.04). Other dietary factors (protein, carbohydrate, calcium, alcohol intake and disordered eating risk) did not influence injury risk (low-moderate certainty evidence).

CONCLUSIONS

Moderate certainty evidence indicates female distance runners with lower energy and total fat intakes are at increased risk of running-related injury, as are runners (combined sexes) with lower dietary fibre intake. Future research should include long duration, high quality prospective cohort studies in male and female runners with clearly defined athletic abilities, consistent injury definition, and standardised statistical analyses.

REVIEW REGISTRATION

PROSPERO # CRD42022323627.

Changes in hormonal profiles during competition preparation in physique athletes

PURPOSE

Physique athletes engage in rigorous competition preparation involving intense energy restriction and physical training to enhance muscle definition. This study investigates hormonal changes and their physiological and performance impacts during such preparation.

METHODS

Participants included female (10 competing (COMP) and 10 non-dieting controls (CTRL)) and male (13 COMP and 10 CTRL) physique athletes. COMP participants were tested 23 weeks before (PRE), one week before (MID), and 23 weeks after the competition (POST). Non-dieting CTRL participants were tested at similar intervals. Measurements included body composition (DXA), muscle cross-sectional area (ultrasound), energy availability (EA) derived by subtracting exercise energy expenditure (EEE) from energy intake (EI) and dividing by fat-free mass (FFM), muscle strength, and various serum hormone concentrations (ACTH, cortisol, estradiol, FSH, IGF-1, IGFBP-3, insulin, and free and total testosterone and SHBG).

RESULTS

During the diet, EA (p < 0.001), IGF-1 (p < 0.001), IGFBP-3 (p < 0.01), and absolute muscle strength (p < 0.01-0.001) decreased significantly in both sexes in COMP. Decreases in IGF-1 were also associated with higher loss in FFM. In males, testosterone (p < 0.01) and free testosterone (p < 0.05) decreased, while SHBG (p < 0.001) and cortisol (p < 0.05) increased. Insulin decreased significantly only in males (p < 0.001). Mood disturbances, particularly increased fatigue in males (p < 0.05), highlighted the psychological strain of competition preparation. All these changes were restored by increased EA during the post-competition recovery period.

CONCLUSION

Significant reductions in IGF-1 and IGFBP-3 during competition preparation may serve as biomarkers for monitoring physiological stress. This study offers valuable insights into hormonal changes, muscle strength, and mood state during energy-restricted intense training.

New approach to identifying elite winter sport athletes' risk of relative energy deficiency in sport (REDs)

Objectives

Relative energy deficiency in sport (REDs) is a syndrome resulting from problematic low energy availability (LEA). Low areal bone mineral density (aBMD) is a primary indicator of LEA, measured by dual X-ray absorptiometry (DXA). High-resolution peripheral quantitative CT (HR-pQCT) is an advanced imaging device that provides measures of volumetric BMD (vBMD), bone microarchitecture, geometry and strength. This study aimed to assess the prevalence of REDs in elite winter sport athletes and to observe the associations in bone parameters using HR-pQCT in athletes identified as at-risk or not at-risk of REDs.

Methods

Participants included 101 elite athletes (24.1±4.4 SD years; 52% female). The REDs Clinical Assessment Tool (CAT2) was used to determine REDs risk. HR-pQCT scans of the non-dominant radius and left tibia were analysed on REDs risk grouping.

Results

17 athletes (17%; 71% female) were at-risk based on the REDs CAT2. After covarying for lean mass, OR suggested a higher likelihood of REDs risk classification for athletes with low cortical thickness, cortical area, total vBMD and bone strength.

Conclusions

Impaired total vBMD, bone strength and cortical bone parameters were approximately twice as likely (OR: 1.9-3.0) in athletes at-risk of REDs. Results agree with the consensus statement that HR-pQCT may identify impaired bone health in athletes at-risk of REDs. Future directions should use HR-pQCT to explore REDs risk longitudinally, using bone change over time, as this may provide greater insight. Using advanced imaging to explore REDs risk in a population of winter high-performance athletes is novel.

Tibial Skeletal Adaptations in Male and Female Marine Corps Officer Candidates Undergoing 10 Weeks of Military Training

Military training improves tibial density, structure, and estimated strength; however, men and women may adapt differently. Most work performed in military populations has assessed changes in bone health during initial entry programs, a timeframe at the beginning of a service member's career when bones may be more adaptable to a novel mechanical stimulus. The purpose of this investigation was to examine changes in tibial volumetric bone mineral density (vBMD), structure, and estimated strength, and biomarkers of bone metabolism (P1NP, osteocalcin, TRAP5b, sclerostin) between male and female candidates measured at the start and end of United States Marine Corps Officer Candidates School (OCS), a 10-week military training program attended by older service members (~ 25 y/o) who may have previous military experience. Peripheral quantitative computed tomography (pQCT) of the tibia (n = 375) and blood draws (n = 385) were performed. Generalized linear mixed effects modeling compared changes between sexes over time. Increases in total and trabecular vBMD were observed at the 4% site in the total sample, but total and cortical vBMD decreased in female candidates at the 66% site. Periosteal circumference at the 38% and 66% sites increased in the total sample. Estimated strength increased similarly in male and female candidates at the 4% and 38% sites but only increased in male candidates at the 66% site. Concentrations of P1NP and osteocalcin increased similarly in both sexes, although sclerostin and TRAP5b decreased only in male candidates. Measures of tibial vBMD, width, and estimated strength increased following OCS consistent with adaptive bone formation.

International Delphi consensus on bone stress injuries in athletes

Bone stress injuries, commonly referred to as stress reactions and stress fractures, represent overuse injuries to bone. These injuries result in physical limitations in activity and can be career-ending for high-level athletes. While bone stress injuries have received increased attention in recent years, international consensus is lacking on definitions, risk factors and strategies for management and prevention. This study aimed to ascertain and improve the level of agreement on bone stress injuries by utilising a three-part modified Delphi approach on (1) pathophysiology, diagnosis, terminology and classification systems; (2) risk factors, screening and prevention; and (3) management and return to sport. A multidisciplinary steering committee initiated the consensus process. A panel of 41 members from six continents was formed to complete three rounds of voting, including experts (scientists and clinicians) and representatives (athletes and coaches). Thirty-three, 28 and 28 panel members completed Delphi rounds 1, 2 and 3, respectively. Consensus was reached on 41 out of 58 statements. Findings from this Delphi study outline a multifactorial approach to identify and manage bone stress injuries and to promote bone health in athletes. This includes recommendations for diagnostic workup and treatment to assist clinicians in caring for patients with bone stress injuries. Finally, this consensus process identifies knowledge gaps and provides a framework for future research to advance the clinical care and prevention of bone stress injuries.

The whole-body and skeletal muscle metabolic response to 14 days of highly controlled low energy availability in endurance-trained females

This study investigated the effects of 14 days low energy availability (LEA) versus optimal energy availability (OEA) in endurance-trained females on substrate utilization, insulin sensitivity, and skeletal muscle mitochondrial oxidative capacity; and the impact of metabolic changes on exercise performance. Twelve endurance-trained females (V̇O2max 55.2 ± 5.1 mL × min-1 × kg-1) completed two 14-day randomized, blinded, cross-over, controlled dietary interventions: (1) OEA (51.9 ± 2.0 kcal × kg fat-free mass (FFM)-1 × day-1) and (2) LEA (22.3 ± 1.5 kcal × kg FFM-1 × day-1), followed by 3 days OEA. Participants maintained their exercise training volume during both interventions (approx. 8 h × week-1 at 79% heart rate max). Skeletal muscle mitochondrial respiratory capacity, glycogen, and maximal activity of CS, HAD, and PFK were unaltered with LEA. 20-min time trial endurance performance was impaired by 7.8% (Δ -16.8 W, 95% CI: -23.3 to -10.4, p < .001) which persisted following 3 days refueling post-LEA (p < .001). Fat utilization was increased post-LEA as evidenced by: (1) 99.4% (p < .001) increase in resting plasma free fatty acids (FFA); (2) 270% (p = .007) larger reduction in FFA in response to acute exercise; and (3) 28.2% (p = .015) increase in resting fat oxidation which persisted during submaximal exercise (p < .001). These responses were reversed with 3 days refueling. Daily glucose control (via CGM), HOMA-IR, HOMA-β, were unaffected by LEA. Skeletal muscle O2 utilization and carbohydrate availability were not limiting factors for aerobic exercise capacity and performance; therefore, whether LEA per se affects aspects of training quality/recovery requires investigation.

Women in space: A review of known physiological adaptations and health perspectives

Exposure to the spaceflight environment causes adaptations in most human physiological systems, many of which are thought to affect women differently from men. Since only 11.5% of astronauts worldwide have been female, these issues are largely understudied. The physiological nuances affecting the female body in the spaceflight environment remain inadequately defined since the last thorough published review on the subject. A PubMed literature search yielded over 2200 publications. Using NASA's 2014 review series 'The effects of sex and gender on adaptation to space' as a benchmark, we identified substantive advancements and persistent knowledge gaps in need of further study from the nearly 600 related articles that have been published since the initial review. This review highlights the most critical issues to mitigate medical risk and promote the success of missions to the Moon and Mars. Salient sex-linked differences observed terrestrially should be studied during upcoming missions, including increased levels of inflammatory markers, coagulation factors and leptin levels following sleep deprivation; correlation between body mass and the severity of spaceflight-associated neuro-ocular syndrome; increased incidence of orthostatic intolerance; increased severity of muscle atrophy and bone loss; differences in the incidence of urinary tract infections; and susceptibility to specific cancers after exposure to ionizing radiation. To optimize health and well-being among all astronauts, it is imperative to prioritize research that considers the physiological nuances of the female body. A more robust understanding of female physiology in the spaceflight environment will support crew readiness for Artemis missions and beyond.

The Influence of Nutrition Intervention on the P1NP and CTX-1 Response to an Acute Exercise Bout: A Systematic Review with Meta-Analysis

BACKGROUND

Although nutrition and exercise both influence bone metabolism, little is currently known about their interaction, or whether nutritional intervention can modulate the bone biomarker response to acute exercise. Improved understanding of the relationships between nutrition, exercise and bone metabolism may have substantial potential to inform nutritional interventions to protect the bone health of exercising individuals, and to elucidate mechanisms by which exercise and nutrition influence bone.

OBJECTIVE

The aim was to synthesise available evidence related to the influence of nutrition on the response of the bone biomarkers procollagen type 1 N-terminal propeptide (P1NP) and C-terminal telopeptide of type 1 collagen (CTX-1) to acute exercise, using a systematic review and meta-analytic approach.

METHODS

Studies evaluating the influence of nutritional status or intervention on the bone biomarker response to an acute exercise bout were included and separated into four categories: (1) feeding status and energy availability, (2) macronutrients, (3) micronutrients and (4) other. Studies conducted on healthy human populations of any age or training status were included. Meta-analysis was conducted when data from at least five studies with independent datasets were available. In the case of insufficient data to warrant meta-analysis, results from individual studies were narratively synthesised and standardised mean effect sizes visually represented.

RESULTS

Twenty-two articles were included. Of these, three investigated feeding status or energy availability, eight macronutrients, eight micronutrients (all calcium) and six other interventions including dairy products or collagen supplementation. Three studies had more than one intervention and were included in all relevant outcomes. The largest and most commonly reported effects were for the bone resorption marker CTX-1. Meta-analysis indicated that calcium intake, whether provided via supplements, diet or infusion, reduced exercise-induced increases in CTX-1 (effect size - 1.1; 95% credible interval [CrI] -  2.2 to - 0.05), with substantially larger effects observed in studies that delivered calcium via direct infusion versus in supplements or foods. Narrative synthesis suggests that carbohydrate supplementation may support bone during acute exercise, via reducing exercise-induced increases in CTX-1. Conversely, a low-carbohydrate/high-fat diet appears to induce the opposite effect, as evidenced by an increased exercise associated CTX-1 response, and reduced P1NP response. Low energy availability may amplify the CTX-1 response to exercise, but it is unclear whether this is directly attributable to energy availability or to the lack of specific nutrients, such as carbohydrate.

CONCLUSION

Nutritional intervention can modulate the acute bone biomarker response to exercise, which primarily manifests as an increase in bone resorption. Ensuring adequate attention to nutritional factors may be important to protect bone health of exercising individuals, with energy, carbohydrate and calcium availability particularly important to consider. Although a wide breadth of data were available for this evidence synthesis, there was substantial heterogeneity in relation to design and intervention characteristics. Direct and indirect replication is required to confirm key findings and to generate better estimates of true effect sizes.

Does Relative Energy Deficiency in Sport (REDs) Syndrome Exist?

Relative energy deficiency in sport (REDs) is a widely adopted model, originally proposed by an International Olympic Committee (IOC) expert panel in 2014 and recently updated in an IOC 2023 consensus statement. The model describes how low energy availability (LEA) causes a wide range of deleterious health and performance outcomes in athletes. With increasing frequency, sports practitioners are diagnosing athletes with "REDs," or "REDs syndrome," based largely upon symptom presentation. The purpose of this review is not to "debunk" REDs but to challenge dogmas and encourage rigorous scientific processes. We critically discuss the REDs concept and existing empirical evidence available to support the model. The consensus (IOC 2023) is that energy availability, which is at the core of REDs syndrome, is impossible to measure accurately enough in the field, and therefore, the only way to diagnose an athlete with REDs appears to be by studying symptom presentation and risk factors. However, the symptoms are rather generic, and the causes likely multifactorial. Here we discuss that (1) it is very difficult to isolate the effects of LEA from other potential causes of the same symptoms (in the laboratory but even more so in the field); (2) the model is grounded in the idea that one factor causes symptoms rather than a combination of factors adding up to the etiology. For example, the model does not allow for high allostatic load (psychophysiological "wear and tear") to explain the symptoms; (3) the REDs diagnosis is by definition biased because one is trying to prove that the correct diagnosis is REDs, by excluding other potential causes (referred to as differential diagnosis, although a differential diagnosis is supposed to find the cause, not demonstrate that it is a pre-determined cause); (4) observational/cross-sectional studies have typically been short duration (< 7 days) and do not address the long term "problematic LEA," as described in the IOC 2023 consensus statement; and (5) the evidence is not as convincing as it is sometimes believed to be (i.e., many practitioners believe REDs is well established). Very few studies can demonstrate causality between LEA and symptoms, most studies demonstrate associations and there is a worrying number of (narrative) reviews on the topic, relative to original research. Here we suggest that the athlete is best served by an unbiased approach that places health at the center, leaving open all possible explanations for the presented symptoms. Practitioners could use a checklist that addresses eight categories of potential causes and involve the relevant experts if and when needed. The Athlete Health and Readiness Checklist (AHaRC) we introduce here simply consists of tools that have already been developed by various expert/consensus statements to monitor and troubleshoot aspects of athlete health and performance issues. Isolating the purported effects of LEA from the myriad of other potential causes of REDs symptoms is experimentally challenging. This renders the REDs model somewhat immune to falsification and we may never definitively answer the question, "does REDs syndrome exist?" From a practical point of view, it is not necessary to isolate LEA as a cause because all potential areas of health and performance improvement should be identified and tackled.

Measurement of energy availability in highly trained male endurance athletes and examination of its associations with bone health and endocrine function

PURPOSE

Despite the introduction of Relative Energy Deficiency in Sport (RED-s) in 2014, there is evidence to suggest that male endurance athletes still present with a high prevalence of low energy availability (LEA). Previous findings suggest that energy availability (EA) status is strongly correlated with impairments in endocrine function such as reduced leptin, triiodothyronine (T3), and insulin, and elevated bone loss. This study aimed to report the current EA status, endocrine function and bone health of highly trained Irish male endurance athletes.

METHODS

In this cross-sectional study, participants (n = 3 triathletes; n = 10 runners) completed a 7-day testing period during the competition season using lab-based measures, to ascertain EA status, hormone level and rates of bone metabolism. Serum blood samples were obtained to assess hormone levels and markers of bone metabolism.

RESULTS

Mean EA was < 30 kcal/kg lean body mass (LBM)/day in 76.9% of athletes. There was a strong association between LEA and low carbohydrate intake, and lower LBM. Mean levels of insulin, IGF-1 and leptin were significantly lower than their reference ranges. Elevated mean concentrations of β-CTX and a mean P1NP: β-CTX ratio < 100, indicated a state of bone resorption.

CONCLUSION

The EA level, carbohydrate intake, hormone status and bone metabolism status of highly trained male endurance athletes are a concern. Based on the findings of this study, more frequent assessment of EA across a season is recommended to monitor the status of male endurance athletes, in conjunction with nutritional education specific to EA and the associated risks.

Assessment of entropy accumulation in human subjects when exposed to low energy availability

Background & aims

Adequate energy availability is essential for the body to maintain its physiological functions and achieve optimal health, especially among athletes. Unfortunately, low energy availability (LEA) is common among athletes, and it has been associated with impairments in health and performance. In contrast, an energy-restricted diet has been linked to longevity, but it is unclear how LEA affects athletes' lifespans. The goal of the present study was to assess the impact of LEA thermodynamically on the lifespan of athletes.

Methods

Data from seven healthy young endurance-trained athletes (24 ± 4 years) who underwent short-term low energy availability (125 (kJ/day) per kg FFM) once with low protein content (LEA-LP; 0.8 g/kg) and with high protein content (LEA-HP; 125 (kJ/day) per kg FFM, 1.7 g/kg), as well as a control diet (CON; 230 (kJ/day) per kg FFM, 1.7 g/kg), were used in the calculations. The athletes followed each diet for five days and expended 67.5 (kJ/day) per kg FFM. entropy generation-based thermodynamic calculations were performed based on the metabolic activity of the athletes, which was determined from oxygen consumption and carbon dioxide production rates.

Results

Low energy availability was successfully induced during LEA-LP (62 ± 8 (kJ/day) per kg FFM; 95%Cl: 53-70) and LEA-HP (64 ± 8 (kJ/day) per kg FFM; 95%Cl: 56-71) diets. Despite of achieving energy deficit of -6658 ± 2110 kJ/day (95%Cl: 8609-(-) 4707) (LEA-LP), -5781 ± 623 (95%Cl: 26591-(-)4707) (LEA-HP) and excessive energy of 772 ± 1915 (95%Cl: 845-2388) (CON) statistical analyses revealed no significant differences in lifespan estimations among diets (CON: 72 ± 8 years (95%Cl: 65-79), LEA-LP: 74 ± 7 years (95%Cl: 68-80), and LEA-HP: 73 ± 11 (95%Cl: 62-83)).

Conclusions

This study suggests valuable insights into the intricate relationship between energy availability, entropy generation, and lifespan among athletes. Whereas entropy generation levels and the lifespan of athletes remained stable depending on diets, the distinguished differences in energy deficiency and energy availability underline the need for a profounder investigation of underlying physiological mechanisms to improve the health and performance of athletes.

Relative Energy Deficiency in Sport (REDs): Endocrine Manifestations, Pathophysiology and Treatments

Research on lean, energy-deficient athletic and military cohorts has broadened the concept of the Female Athlete Triad into the Relative Energy Deficiency in Sport (REDs) syndrome. REDs represents a spectrum of abnormalities induced by low energy availability (LEA), which serves as the underlying cause of all symptoms described within the REDs concept, affecting exercising populations of either biological sex. Both short- and long-term LEA, in conjunction with other moderating factors, may produce a multitude of maladaptive changes that impair various physiological systems and adversely affect health, well-being, and sport performance. Consequently, the comprehensive definition of REDs encompasses a broad spectrum of physiological sequelae and adverse clinical outcomes related to LEA, such as neuroendocrine, bone, immune, and hematological effects, ultimately resulting in compromised health and performance. In this review, we discuss the pathophysiology of REDs and associated disorders. We briefly examine current treatment recommendations for REDs, primarily focusing on nonpharmacological, behavioral, and lifestyle modifications that target its underlying cause-energy deficit. We also discuss treatment approaches aimed at managing symptoms, such as menstrual dysfunction and bone stress injuries, and explore potential novel treatments that target the underlying physiology, emphasizing the roles of leptin and the activin-follistatin-inhibin axis, the roles of which remain to be fully elucidated, in the pathophysiology and management of REDs. In the near future, novel therapies leveraging our emerging understanding of molecules and physiological axes underlying energy availability or lack thereof may restore LEA-related abnormalities, thus preventing and/or treating REDs-related health complications, such as stress fractures, and improving performance.

Original investigation: manipulating energy availability in male endurance runners: a randomised controlled trial

This study investigated the effect of 4 days low energy availability (LEA) on physiological markers and mood states in male endurance runners. Twelve participants (mean (standard deviation); age: 25.8 (3.8) years; fat-free mass (FFM): 52.8 (5.5) kg) completed three 4-day conditions: adequate energy availability (AEA): 45 kcal/kg FFM/day; LEA1: 30 kcal/kg FFM/day; and LEA2: 15 kcal/kg FFM/day, in a randomized order. Participants ran on a treadmill at 65% of V̇O2max until they expended 15 kcal/kg FFM/day of energy. Energy intake was adjusted to achieve the desired energy availability. Pre- and post-measurements of bone turnover, metabolism, testosterone and estradiol (plasma), resting metabolic rate (indirect calorimetry), and mood states (Brunel Mood Scale) were assessed. The results reported a significant decrease in testosterone (condition × time interaction, p = 0.03) occurred on LEA2 (Pre: 23.8 (7.0) nmol/L vs. Post: 20.3 (7.7) nmol/L) compared with AEA (Pre: 22.9 (5.5) nmol/L vs. Post: 23.3 (6.1) nmol/L) or LEA1 (Pre: 23.6 (8.6) nmol/L vs. Post: 20.9 (8.8) nmol/L). Fatigue level significantly increased (condition × time interaction, p = 0.02) in LEA2 (Pre: 3.5 (1.7) vs. Post: 6.5 (2.9)) but did not change in AEA (Pre: 2.8 (1.5) vs. Post: 2.5 (2.7)) or LEA1 (Pre: 2.8(2.4) vs. Post: 2.9 (2.0)). Other measures were unaffected by the interventions. In conclusion, this study suggests that testosterone and fatigue may serve as early indicators of LEA in male runners. However, other physiological markers and mood states appeared largely unaffected, aligning with existing literature indicating minimal disruption of physiological functions during acute LEA in male athletes. Study registration: Australian New Zealand Clinical Trials Registry (Trial No.: 381278).

An Opinion on the Interpretation of Bone Turnover Markers Following Acute Exercise or Nutrition Intervention and Considerations for Applied Research

It is important for athlete and public health that we continue to develop our understanding of the effects of exercise and nutrition on bone health. Bone turnover markers (BTMs) offer an opportunity to accelerate the progression of bone research by revealing a bone response to exercise and nutrition stimuli far more rapidly than current bone imaging techniques. However, the association between short-term change in the concentration of BTMs and long-term bone health remains ambiguous. Several other limitations also complicate the translation of acute BTM data to applied practice. Importantly, several incongruencies exist between the effects of exercise and nutrition stimuli on short-term change in BTM concentration compared with long-term bone structural outcomes to similar stimuli. There are many potential explanations for these inconsistencies, including that short-term study designs fail to encompass a full remodeling cycle. The current article presents the opinion that data from relatively acute studies measuring BTMs may not be able to reliably inform applied practice aiming to optimize bone health. There are important factors to consider when interpreting or translating BTM data and these are discussed.

Beyond Menstrual Dysfunction: Does Altered Endocrine Function Caused by Problematic Low Energy Availability Impair Health and Sports Performance in Female Athletes?

Low energy availability, particularly when problematic (i.e., prolonged and/or severe), has numerous negative consequences for health and sports performance as characterized in relative energy deficiency in sport. These consequences may be driven by disturbances in endocrine function, although scientific evidence clearly linking endocrine dysfunction to decreased sports performance and blunted or diminished training adaptations is limited. We describe how low energy availability-induced changes in sex hormones manifest as menstrual dysfunction and accompanying hormonal dysfunction in other endocrine axes that lead to adverse health outcomes, including negative bone health, impaired metabolic activity, undesired outcomes for body composition, altered immune response, problematic cardiovascular outcomes, iron deficiency, as well as impaired endurance performance and force production, all of which ultimately may influence athlete health and performance. Where identifiable menstrual dysfunction indicates hypothalamic-pituitary-ovarian axis dysfunction, concomitant disturbances in other hormonal axes and their impact on the athlete's health and sports performance must be recognized as well. Given that the margin between podium positions and "losing" in competitive sports can be very small, several important questions regarding low energy availability, endocrinology, and the mechanisms behind impaired training adaptations and sports performance have yet to be explored.

Low energy availability increases immune cell formation of reactive oxygen species and impairs exercise performance in female endurance athletes

INTRODUCTION

The effects of low energy availability (LEA) on the immune system are poorly understood. This study examined the effects of 14 days of LEA on immune cell redox balance and inflammation at rest and in response to acute exercise, and exercise performance in female athletes.

METHODS

Twelve female endurance athletes (age: 26.8 ± 3.4 yrs, maximum oxygen uptake (V˙O2max): 55.2 ± 5.1 mL × min-1 × kg-1) were included in a randomized, single-blinded crossover study. They were allocated to begin with either 14 days of optimal energy availability diet (OEA, 52 ± 2 kcal × kg fat free mass (FFM)-1 × day-1) or LEA diet (22 ± 2 kcal × kg FFM-1 × day-1), followed by 3 days of refueling (OEA) with maintained training volume. Peripheral blood mononuclear cells (PBMCs) were isolated, and plasma obtained at rest before and after each dietary period. The PBMCs were used for analysis of mitochondrial respiration and H2O2 emission and specific proteins. Exercise performance was assessed on cycle by a 20-min time trial and time to exhaustion at an intensity corresponding to ∼110 % V˙O2max).

RESULTS

LEA was associated with a 94 % (P = 0.003) increase in PBMC NADPH oxidase 2 protein content, and a 22 % (P = 0.013) increase in systemic cortisol. LEA also caused an alteration of several inflammatory related proteins (P < 0.05). Acute exercise augmented H2O2 emission in PBMCs (P < 0.001) following both OEA and LEA, but to a greater extent following LEA. LEA also reduced the mobilization of white blood cells with acute exercise. After LEA, performance was reduced in both exercise tests (P < 0.001), and the reduced time trial performance remained after the 3 days of refueling (P < 0.001).

CONCLUSION

14 days of LEA in female athletes increased cortisol levels and had a pronounced effect on the immune system, including increased capacity for ROS production, altered plasma inflammatory proteome and lowered exercise induced mobilization of leukocytes. Furthermore, LEA resulted in a sustained impairment in exercise performance.

Energy expenditure, intake and availability in female soccer players via doubly labelled water: Are we misrepresenting low energy availability?

Female soccer players have been identified as presenting with low energy availability (LEA), though the prevalence of LEA may be overestimated given inaccuracies associated with self-reporting dietary intakes. Accordingly, we aimed to quantify total daily energy expenditure (TDEE) via the doubly labelled water (DLW) method, energy intake (EI) and energy availability (EA). Adolescent female soccer players (n = 45; 16 ± 1 years) completed a 9-10 day 'training camp' representing their national team. Absolute and relative TDEE was 2683 ± 324 and 60 ± 7 kcal kg-1 fat free mass (FFM), respectively. Mean daily EI was lower (P < 0.01) when players self-reported using the remote food photography method (RFPM) (2047 ± 383 kcal day-1) over a 3-day period versus DLW derived EI estimates accounting for body mass (BM) changes (2545 ± 518 kcal day-1) over 7-8 days, representing a mean daily Δ of 499 ± 526 kcal day-1 and 22% error when using the RFPM. Estimated EA was different (P < 0.01) between methods (DLW: 48 ± 14 kcal kg-1 FFM, range: 22-82; RFPM: 37 ± 8 kcal kg-1 FFM, range: 22-54), such that prevalence of LEA (<30 kcal kg-1 FFM) was lower in DLW compared with RFPM (5% vs. 15%, respectively). Data demonstrate the potential to significantly underestimate EI when using self-report methods. This approach can therefore cause a misrepresentation and an over-prevalence of LEA, which is the underlying aetiology of 'relative energy deficiency in sport' (REDs). HIGHLIGHTS: What is the central question of this study? Do self-reported dietary intakes (via remote food photography method, RFPM) overestimate low energy availability (LEA) prevalence in female soccer players compared with energy intake evaluation from the doubly labelled water (DLW) method? What is the main finding and its importance? Estimated energy availability is greater with the DLW method compared with RFPM, such that the prevalence of LEA is greater when self-reporting dietary intakes. Accordingly, data demonstrate the potential to misrepresent the prevalence of LEA, an underlying factor in the aetiology of 'relative energy deficiency in sport' (REDs).

Identifying and Analyzing Low Energy Availability in Athletes: The Role of Biomarkers and Red Blood Cell Turnover

Low energy availability (LEA) is a growing concern that can lead to several problems for athletes. However, adaptation to LEA occurs to maintain balance over time, making diagnosis difficult. In this review, we categorize LEA into two phases: the initial phase leading to adaptation and the phase in which adaptation is achieved and maintained. We review the influence of LEA on sports performance and health and discuss biomarkers for diagnosing LEA in each phase. This review also proposes future research topics for diagnosing LEA, with an emphasis on the recently discovered association between red blood cell turnover and LEA.

A literature review of biomarkers used for diagnosis of relative energy deficiency in sport

Introduction

The review aims to summarize the markers used in diagnosing relative energy deficiency in sport (REDs) and compare them with the REDs CAT2 score.

Methods

A systematic search was performed in the PubMed, Web of Science, and SPORTDiscus databases during April 2023. The descriptors used were "athlete" AND "REDs," along with respective entry terms. The selection process followed the PRISMA 2020 recommendations, identifying 593 records, from which 13 studies were ultimately selected. Seventy-nine markers were identified and categorized into six groups: bone mineral density (BMD), metabolic resting rate, blood biomarkers, anthropometrics, nutritional intake, and performance parameters. The most frequently utilized biomarkers included BMD, anthropometric parameters (e.g., body mass index, body mass, and fat mass), and the triiodothyronine (T3) concentration.

Results

According to the REDs CAT2 pointed indicators, the biomarkers varied among the studies, while 7 out of the 13 included studies achieved a ≥60% agreement rate with this tool. The prevalence of low energy availability, an etiological factor in the development of REDs, was detected in 4 out of 13 studies, with an average of 39.5%.

Conclusion

In conclusion, this review highlights the most commonly used markers in diagnosing REDs, such as BMD, anthropometric parameters, and T3 hormone concentration. Due to the current inconsistencies, standardizing diagnostic methodologies is crucial for future research. By focusing on widely used markers, this review aids future research planning and result interpretation and points out the ongoing need for methodological consistency in evolving diagnostic tools.

Systematic Review Registration

https://www.crd.york.ac.uk/, PROSPERO (CRD42022320007).

Contemporary Issue: Health and Safety of Female Wrestlers

ABSTRACT

Female wrestling has grown exponentially over the past decade. Within the United States, 46 states now recognize female high school wrestling, and 153 colleges have programs. It is on track to become an NCAA championship-level sport in 2026. A primary health and safety risk among this cohort pertains to rapid weight loss strategies. These can lead to intentional caloric restriction and decreased body fatness, with the perceived goal of attaining a competitive advantage. Low energy availability and low body fatness are associated with a number of health concerns including menstrual dysfunction and loss of bone mineral density in girls and women. The current recommendation of 12% as a minimum for percentage body fat is very likely too low, opening the door for health perturbations among this population. The minimum threshold might more appropriately fall within the range of 18% to 20%. Body fat assessment methods, primarily skinfold measures that are used to guide weight class selection, have not been adequately validated among this population and therefore should be an area of research focus, while also exploring alternative assessment techniques. Further, we recommend that weight cycling, restrictive energy intake, and intentional dehydration be avoided. Research should assess the effects of frequent weight cycling (to "make weight") and prolonged periods of low body fat on the reproductive and bone health of these athletes. Finally, research and clinical evaluations on female wrestlers are limited, and we offer a list of research priorities for future investigation into this contemporary issue.

A real-life snapshot: Evaluating exposures to low energy availability in male athletes from various sports

Problematic low energy availability (LEA) is the underlying cause of relative energy deficiency in sport (REDs). Male specific etiology, as well as the duration and degree of LEA exposures resulting in REDs remain to be adequately described. The present study aimed to assess occurrences of LEA (energy availability [EA] <25 kcal/kg fat-free mass/day) in male athletes from various sports over 7 days. Associations between number of LEA days, physiological measures, and body image concerns were subsequently evaluated. The athletes recorded their weighed food intakes and training via photo-assisted mobile application. Body composition and resting metabolic rates were measured, and venous blood samples collected for assessments of hormonal and nutrition status. Participants also answered the Low Energy Availability in Males Questionnaire (LEAM-Q), Eating Disorder Examination-Questionnaire Short (EDE-QS), Exercise Addiction Inventory (EAI), and Muscle Dysmorphic Disorder Inventory (MDDI). Of 19 participants, 13 had 0-2, 6 had 3-5, and none had 6-7 LEA days. No associations were found between the number of LEA days with the physiological and body image outcomes, although those with greatest number of LEA days had highest EEE but relatively low dietary intakes. In conclusion, this group displayed considerable day-to-day EA fluctuations but no indication of problematic LEA.

Patterns of energy availability and carbohydrate intake differentiate between adaptable and problematic low energy availability in female athletes

Background

Problematic low energy availability (EA) is the underlying culprit of relative energy deficiency in sport (REDs), and its consequences have been suggested to be exacerbated when accompanied by low carbohydrate (CHO) intakes.

Objectives

This study compared dietary intake, nutrition status and occurrence of REDs symptoms in groups of female athletes, displaying different patterns of EA and CHO intake.

Methods

Female athletes (n = 41, median age 20.4 years) from various sports weighed and recorded their food intake and training for 7 consecutive days via a photo-assisted mobile application. Participants were divided into four groups based on patterns of EA and CHO intakes: sufficient to optimal EA and sufficient to optimal CHO intake (SEA + SCHO), SEA and low CHO intake (SEA + LCHO), low energy availability and SCHO (LEA + SCHO), and LEA and LCHO (LEA + LCHO). SEA patterns were characterised by EA ≥30 and LEA by EA <30 kcal/kg fat free mass, and SCHO patterns characterised by CHO intake ≥3.0 and LCHO <3.0 g/kg body weight for most of the registered days. Body composition was measured with dual energy x-ray absorptiometry, resting metabolic rate with indirect calorimetry and serum blood samples were collected for evaluation of nutrition status. Behavioural risk factors and self-reported symptoms of REDs were assessed with the Low Energy Availability in Females Questionnaire, Eating Disorder Examination Questionnaire Short (EDE-QS), Exercise Addiction Inventory, and Muscle Dysmorphic Disorder Inventory.

Results

In total, 36.6% were categorised as SEA + SCHO, of which 5/16 were ball sport, 7/10 endurance, 1/7 aesthetic, 2/5 weight-class, and 0/3 weight-class athletes. Of LEA + LCHO athletes (19.5% of all), 50% came from ball sports. Aesthetic and endurance athletes reported the greatest training demands, with weekly training hours higher for aesthetic compared to ball sports (13.1 ± 5.7 vs. 6.7 ± 3.4 h, p = 0.012). Two LEA + LCHO and one SEA + LCHO athlete exceeded the EDE-QS cutoff. LEA + LCHO evaluated their sleep and energy levels as worse, and both LEA groups rated their recovery as worse compared to SEA + SCHO.

Conclusion

Repeated exposures to LEA and LCHO are associated with a cluster of negative implications in female athletes. In terms of nutrition strategies, sufficient EA and CHO intakes appear to be pivotal in preventing REDs.

Low Energy Availability Followed by Optimal Energy Availability Does Not Benefit Performance in Trained Females

PURPOSE

Short periods of reduced energy availability are commonly undertaken by athletes to decrease body mass, possibly improve the power-to-mass ratio, and enhance physical performance. Our primary aim was to investigate the impact of 10 d of low energy availability (LEA) followed by 2 d of optimal energy availability (OEA) on physical performance parameters in trained females. Second, physiological markers at the whole-body and molecular level related to performance were evaluated.

METHODS

Thirty young trained eumenorrheic females were matched in pairs based on training history and randomized to a 10-d intervention period of LEA (25 kcal·fat-free mass (FFM) -1 ·d -1 ) or OEA (50 kcal·FFM -1 ·d -1 ) along with supervised exercise training. Before the intervention, participants underwent a 5-d run-in period with OEA + supervised exercise training. After the LEA intervention, 2 d of recovery with OEA was completed. Participants underwent muscle biopsies, blood sampling, physical performance tests, body composition measurements, and resting metabolic rate measurements. A linear mixed model was used with group and time as fixed effects and subject as random effects.

RESULTS

Compared with OEA, LEA resulted in reduced body mass, muscle glycogen content, repeated sprint ability, 4-min time-trial performance, and rate of force development of the knee extensors (absolute values; P < 0.05). Two days of recovery restored 4-min time-trial performance and partly restored repeated sprint ability, but performance remained inferior to the OEA group. When the performance data were expressed relative to body mass, LEA did not enhance performance.

CONCLUSIONS

Ten days of LEA resulted in impaired performance (absolute values), with concomitant reductions in muscle glycogen. Two days of recovery with OEA partially restored these impairments, although physical performance (absolute values) was still inferior to being in OEA. Our findings do not support the thesis that LEA giving rise to small reductions in body mass improves the power-to-mass ratio and thus increases physical performance.

Bone health and the masters runner

Masters runners are often defined as those ages 35 years and older who train and compete in running events. These runners represent a growing population of the overall running community and experience running-related injuries including bone stress injuries (BSIs). Similar to younger runners, health considerations in masters runners include the goal to optimize bone health with focus on mitigating age-associated loss of bone strength and preventing BSIs through a combination of ensuring appropriate physical activity, optimizing nutrition, and correcting faulty biomechanics. Importantly, BSIs in masters runners may include characteristics of both overuse injury from insufficient recovery and failure of bone weakened by age-related loss of bone (insufficiency fractures). This narrative review covers the limited available research on strategies to optimize bone health in masters runners. Applying knowledge on masters athletes and extrapolating from other populations, we propose strategies on treatment and prevention of BSIs. Finally, the review highlights gaps in knowledge that require further age-specific discoveries to advance treatment and prevention.

Sex differences in energy balance, body composition, and metabolic and endocrine markers during prolonged arduous military training

This study investigated sex differences in energy balance, body composition, and metabolic and endocrine markers during prolonged military training. Twenty-three trainees (14 women) completed 44-wk military training (three terms of 14 wk with 2-wk adventurous training). Dietary intake and total energy expenditure were measured over 10 days during each term by weighed food and doubly labeled water. Body composition was measured by dual-energy X-ray absorptiometry (DXA) at baseline and at the end of each term. Circulating metabolic and endocrine markers were measured at baseline and at the end of terms 2 and 3. Absolute energy intake and total energy expenditure were higher, and energy balance was lower, for men than women (P ≤ 0.008). Absolute energy intake and balance were lower, and total energy expenditure was higher, during term 2 than terms 1 and 3 (P < 0.001). Lean mass did not change with training (P = 0.081). Fat mass and body fat increased from term 1 to terms 2 and 3 (P ≤ 0.045). Leptin increased from baseline to terms 2 and 3 in women (P ≤ 0.002) but not in men (P ≥ 0.251). Testosterone and free androgen index increased from baseline to term 3 (P ≤ 0.018). Free thyroxine (T4) decreased and thyroid-stimulating hormone (TSH) increased from baseline to term 2 and term 3 (P ≤ 0.031). Cortisol decreased from baseline to term 3 (P = 0.030). IGF-I and total triiodothyronine (T3) did not change with training (P ≥ 0.148). Men experienced greater energy deficits than women during military training due to higher total energy expenditure.NEW & NOTEWORTHY Energy deficits are common in military training and can result in endocrine and metabolic disturbances. This study provides first investigation of sex differences in energy balance, body composition, and endocrine and metabolic markers in response to prolonged and arduous military training. Men experienced greater energy deficits than women due to higher energy expenditure, which was not compensated for by increased energy intake. These energy deficits were not associated with decreases in fat or lean mass or metabolic or endocrine function.

Characteristics of bone mineral density in patients with functional hypothalamic amenorrhoea and its association with reproductive hormones and body composition

OBJECTIVE

Bone mineral density (BMD) is typically reduced in patients with female athlete triad (FAT) and anorexia nervosa (AN). However, bone health in most patients with functional hypothalamic amenorrhoea (FHA), who may not suffer from severe energy deficiency, has not received adequate attention in clinical practice. This study aimed to investigate BMD and its association with clinical and endocrine features in individuals with FHA and to provide clinical evidence for improving bone loss and preventing osteoporosis in FHA.

DESIGN

To assess the bone status of patients with FHA and investigate its association with various clinical and endocrinological characteristics.

PATIENTS

We retrospectively analysed 80 patients with FHA who attended the Obstetrics and Gynecology Hospital of Fudan University from January 2022 to March 2023.

MEASUREMENTS

The levels of reproductive hormones, including luteinising hormone (LH), follicle-stimulating hormone, oestradiol (E2 ) and total testosterone (TT), were examined at the time of initial diagnosis, and a body composition analyser was used to measure body fat percentage (BF%), lean body mass (LBM) and segmental muscle/fat. Dual-emission X-ray absorptiometry was used to measure lumbar spine BMD and femoral neck BMD in patients with FHA, and the Z score was calculated.

RESULTS

The study cohort consisted of 80 female patients with FHA. The average age of the patients was 24.64 ± 6.02 years, and their body mass index (BMI) was 19.47 ± 2.86 kg/m2 . The duration of weight loss was 12 (6, 24) months, while the duration of oligo/amenorrhoea was 12 (4.5, 24) months. The mean degree of weight loss was 18.39 ± 9.53%. Low BMD were present in 15% of patients with FHA at the lumbar spine and/or femoral neck; 12.5% and 10% had low bone mass at the lumbar spine and femoral neck, respectively. The low bone mass group experienced a longer period of weight loss than the normal group [24 (16.5, 60) vs. 12 (4.5, 24) months, p = .037]. In addition, the abnormal group had a lower BMR (basal metabolic rate, BMR) [1158 ± 85 vs. 1231 ± 91 kcal/day, p = .011] and lower bone mineral content [2.15 ± 0.26 vs. 2.43 ± 0.31 kg, p = .009] than the normal group. Both LBMD and femoral neck BMD (Fn BMD) were positively correlated with BMI, BF%, LBM, and regional muscle/fat mass (all p < .05). There was also a positive correlation between LBMD and basal LH levels (p = .009) and waist-to-hip ratio (p = .034), whereas Fn BMD was positively correlated with TT levels (p = .029). Multiple linear regression analysis showed that LBM was positively associated with LBMD (β = .007, 95% confidence interval [CI] = 0.004-0.009, p < .001), while trunk muscle mass was positively associated with Fn BMD (β = .046, 95% CI = 0.013-0.080, p = .008).

CONCLUSION

Fifteen percent of the patients with FHA exhibited low bone mass, a condition associated with prolonged weight loss. The basal LH and TT levels showed positive correlations with LBMD and Fn BMD, respectively. Meanwhile, BMR levels, BMI, BF%, and muscle mass were all positively correlated with LBMD and Fn BMD. Clinically, we should be attentive to suboptimal bone health in patients with FHA and take early screening, diagnosis and intervention measures, especially appropriate muscle mass gain, to prevent the onset of osteoporosis and fragility fractures in the long term.

Hormonal contraception for female athletes presents special needs and concerns

PURPOSE

Oral contraceptives (OCs) are commonly used by female athletes raising concerns regarding the possible adverse effects of OCs on physical performance, musculoskeletal injuries, and bone density. We aimed to review all current studies on the physiological effects of OCs in physically active women.

MATERIALS AND METHODS

A review of literature in electronic search in PubMed and Google Scholar databases from December 2002 to December 2022 using relevant keywords. The reference lists of the articles found eligible were also reviewed.

RESULTS

Out of 344 articles in the initial database, 54 clinical studies were eligible for inclusion in our literature review. OCs are used by about two-thirds of female athletes. Current research suggests that OCs' effects on endurance performance and muscle strength are mostly reassuring. OCs do not seem to have a major negative impact on bone health or sports injuries. In fact, new data suggests that they may even significantly reduce the risk of anterior cruciate ligament (ACL) injury.

CONCLUSIONS

OCs can be safely used by young female athletes, who may also benefit from better menstrual cycle control. OCs offer newly realised protection from ACL injuries. The use of OCs must be carefully individualised according to their preferences, expectations, and experience.

Female Athlete Triad and Relative Energy Deficiency in Sport (REDs): Nutritional Management

The female athlete triad (TRIAD) is a spectrum of disorders involving low energy availability (LEA), low bone mineral density, and menstrual disorders. It is increasingly common to use the term 'relative energy deficiency in sport' (RED), emphasising the extensive impact of LEA on the body. The aim of this narrative review was to gather original research encompassing female athletes across various sports as well as to collect findings on the potential of a nutrition-focused approach to prevent or treat the aforementioned disorders. A comprehensive search was conducted in PubMed and Scopus. Several challenges were identified regarding the adequacy of the energy availability, protein, and carbohydrate requirements in the diets of female athletes. Moreover, insufficient intake of vitamin D has been observed across all athlete groups studied. This insufficiency also extends to the average requirement for Ca, Mg, the Ca/P ratio, Zn, and Fe. To address those concerns, a nutritional approach is proposed in the latter part of this review. The factors that can improve the absorption of micronutrients have also been discussed. The TRIAD/REDs affect an ever-growing number of women and require appropriate therapeutic management, particularly through nutritional care. Therefore, cooperation within an interdisciplinary team comprising a physician, nutritionist, physiotherapist, and psychologist is crucial.

Physiological Perturbations in Combat Sports: Weight Cycling and Metabolic Function-A Narrative Review

Combat sports athletes seeking a competitive edge often engage in weight management practices to become larger than their opponents, which ultimately includes periods of gradual weight loss, rapid weight loss, and weight regain. This pattern of weight loss and regain is known as weight cycling and often includes periods of low energy availability, making combat sports athletes susceptible to metabolic dysfunction. This narrative review represents an effort to explore the metabolic perturbations associated with weight cycling and outline the short-, medium-, and long-term effects on metabolic flexibility, function, and health. The short-term effects of rapid weight loss, such as a reduced metabolic rate and alterations to insulin and leptin levels, may prelude the more pronounced metabolic disturbances that occur during weight regain, such as insulin resistance. Although definitive support is not currently available, this cycle of weight loss and regain and associated metabolic changes may contribute to metabolic syndrome or other metabolic dysfunctions over time.

Direct and indirect impact of low energy availability on sports performance

Low energy availability (LEA) occurs inadvertently and purposefully in many athletes across numerous sports; and well planned, supervised periods with moderate LEA can improve body composition and power to weight ratio possibly enhancing performance in some sports. LEA however has the potential to have negative effects on a multitude of physiological and psychological systems in female and male athletes. Systems such as the endocrine, cardiovascular, metabolism, reproductive, immune, mental perception, and motivation as well as behaviors can all be impacted by severe (serious and/or prolonged or chronic) LEA. Such widely diverse effects can influence the health status, training adaptation, and performance outcomes of athletes leading to both direct changes (e.g., decreased strength and endurance) as well as indirect changes (e.g., reduced training response, increased risk of injury) in performance. To date, performance implications have not been well examined relative to LEA. Therefore, the intent of this narrative review is to characterize the effects of short-, medium-, and long-term exposure to LEA on direct and indirect sports performance outcomes. In doing so we have focused both on laboratory settings as well as descriptive athletic case-study-type experiential evidence.

Nutritional intake and anthropometric characteristics are associated with endurance performance and markers of low energy availability in young female cross-country skiers

BACKGROUND

Low energy availability (LEA) can have negative performance consequences, but the relationships between LEA and performance are poorly understood especially in field conditions. In addition, little is known about the contribution of macronutrients to long-term performance. Therefore, the aim of this study was to evaluate if energy availability (EA) and macronutrient intake in a field-based situation were associated with laboratory-measured performance, anthropometric characteristics, blood markers, training volume, and/or questionnaire-assessed risk of LEA in young female cross-country (XC) skiers. In addition, the study aimed to clarify which factors explained performance.

METHODS

During a one-year observational study, 23 highly trained female XC skiers and biathletes (age 17.1 ± 1.0 years) completed 3-day food and training logs on four occasions (September-October, February-March, April-May, July-August). Mean (±SD) EA and macronutrient intake from these 12 days were calculated to describe yearly overall practices. Laboratory measurements (body composition with bioimpedance, blood hormone concentrations, maximal oxygen uptake (VO_2max), oxygen uptake (VO₂) at 4 mmol·L^-1 lactate threshold (OBLA), double poling (DP) performance (time to exhaustion), counter movement jump (height) and the Low Energy Availability in Females Questionnaire (LEAF-Q)) were completed at the beginning (August 2020, M₁) and end of the study (August 2021, M₂). Annual training volume between measurements was recorded using an online training diary.

RESULTS

The 12-day mean EA (37.4 ± 9.1 kcal·kg FFM^-1·d^-1) and carbohydrate (CHO) intake (4.8 ± 0.8 g·kg^-1·d^-1) were suboptimal while intake of protein (1.8 ± 0.3 g·kg^-1·d^-1) and fat (31 ± 4 E%) were within recommended ranges. Lower EA and CHO intake were associated with a higher LEAF-Q score (r  = 0.44, p  = 0.042; r  = 0.47, p  = 0.026). Higher CHO and protein intake were associated with higher VO_2max (r  = 0.61, p  = 0.005; r  = 0.54, p  = 0.014), VO₂ at OBLA (r  = 0.63, p  = 0.003; r  = 0.62, p  = 0.003), and DP performance at M₂ (r  = 0.42, p  = 0.051; r  = 0.44, p  = 0.039). Body fat percentage (F%) was negatively associated with CHO and protein intake (r = -0.50, p  = 0.017; r = -0.66, p  = 0.001). Better DP performance at M₂ was explained by higher training volume (R²  = 0.24, p  = 0.033) and higher relative VO_2max and VO₂ at OBLA at M₂ by lower F% (R²  = 0.44, p  = 0.004; R²  = 0.47, p  = 0.003). Increase from M₁ to M₂ in DP performance was explained by a decrease in F% (R²  = 0.25, p  = 0.029).

CONCLUSIONS

F%, and training volume were the most important factors explaining performance in young female XC skiers. Notably, lower F% was associated with higher macronutrient intake, suggesting that restricting nutritional intake may not be a good strategy to modify body composition in young female athletes. In addition, lower overall CHO intake and EA increased risk of LEA determined by LEAF-Q. These findings highlight the importance of adequate nutritional intake to support performance and overall health.

Free-living competitive racewalkers and runners with energy availability estimates of <35 kcal·kg fat-free mass-1·day-1 exhibit peak serum progesterone concentrations indicative of ovulatory disturbances: a pilot study

Introduction

The release of luteinising hormone (LH) before ovulation is disrupted during a state of low energy availability (EA). However, it remains unknown whether a threshold EA exists in athletic populations to trigger ovulatory disturbances (anovulation and luteal phase deficiency) as indicated by peak/mid-luteal serum progesterone concentration (Pk-PRG) during the menstrual cycle.

Methods

We assessed EA and Pk-PRG in 15 menstrual cycles to investigate the relationship between EA and Pk-PRG in free-living, competitive (trained-elite) Guatemalan racewalkers (n = 8) and runners (n = 7) [aged: 20 (14-41) years; post-menarche: 5 (2-26) years; height: 1.53 ± 0.09 m; mass: 49 ± 6 kg (41 ± 5 kg fat-free mass "FFM")]. EA was estimated over 7 consecutive days within the follicular phase using food, training, and physical activity diaries. A fasted blood sample was collected during the Pk-PRG period, 6-8 days after the LH peak, but before the final 2 days of each cycle. Serum progesterone concentration was quantified using electrochemiluminescence immunoassay.

Results

Participants that reported an EA of <35 kcal·kg FFM-1·day-1 (n = 7) exhibited ovulatory disturbances (Pk-PRG ≤9.40 ng·mL-1). Athletes with EA ≥36 kcal·kg FFM-1·day-1 (n = 8) recorded "normal"/"potentially fertile" cycles (Pk-PRG >9.40 ng·mL-1), except for a single racewalker with the lowest reported protein intake (1.1 g·kg body mass-1·day-1). EA was positively associated with Pk-PRG [r(9) = 0.79, 95% confidence interval (CI): 0.37-0.94; p = 0.003; 1 - β = 0.99] after excluding participants (n = 4) that likely under-reported/reduced their dietary intake.

Conclusions

The result from the linear regression analysis suggests that an EA ≥ 36 kcal·kg FFM-1·day-1 is required to achieve "normal ovulation." The threshold EA associated with ovulatory disturbances in athletes and non-invasive means of monitoring the ovulatory status warrant further research.

Physical performance during energy deficiency in humans: An evolutionary perspective

Energy deficiency profoundly disrupts normal endocrinology, metabolism, and physiology, resulting in an orchestrated response for energy preservation. As such, despite energy deficit is typically thought as positive for weight-loss and treatment of cardiometabolic diseases during the current obesity pandemic, in the context of contemporary sports and exercise nutrition, chronic energy deficiency is associated to negative health and athletic performance consequences. However, the evidence of energy deficit negatively affecting physical capacity and sports performance is unclear. While severe energy deficiency can negatively affect physical capacity, humans can also improve aerobic fitness and strength while facing significant energy deficit. Many athletes, also, compete at an elite and world-class level despite showing clear signs of energy deficiency. Maintenance of high physical capacity despite the suppression of energetically demanding physiological traits seems paradoxical when an evolutionary viewpoint is not considered. Humans have evolved facing intermittent periods of food scarcity in their natural habitat and are able to thrive in it. In the current perspective it is argued that when facing limited energy availability, maintenance of locomotion and physical capacity are of high priority given that they are essential for food procurement for survival in the habitat where humans evolved. When energetic resources are limited, energy may be allocated to tasks essential for survival (e.g. locomotion) while minimising energy allocation to traits that are not (e.g. growth and reproduction). The current perspective provides a model of energy allocation during energy scarcity supported by observation of physiological and metabolic responses that are congruent with this paradigm.

Comparison of Bone Quality Among Winter Endurance Athletes with and Without Risk Factors for Relative Energy Deficiency in Sport (REDs): A Cross-Sectional Study

Relative Energy Deficiency in Sport (REDs) is a syndrome describing the relationship between prolonged and/or severe low energy availability and negative health and performance outcomes. The high energy expenditures incurred during training and competition put endurance athletes at risk of REDs. The objective of this study was to investigate differences in bone quality in winter endurance athletes classified as either low-risk versus at-risk for REDs. Forty-four participants were recruited (M = 18; F = 26). Bone quality was assessed at the distal radius and tibia using high resolution peripheral quantitative computed tomography (HR-pQCT), and at the hip and spine using dual X-ray absorptiometry (DXA). Finite element analysis was used to estimate bone strength. Participants were grouped using modified criteria from the REDs Clinical Assessment Tool Version 1. Fourteen participants (M = 3; F = 11), were classified as at-risk of REDs (≥ 3 risk factors). Measured with HR-pQCT, cortical bone area (radius) and bone strength (radius and tibia) were 6.8%, 13.1% and 10.3% lower (p = 0.025, p = 0.033, p = 0.027) respectively, in at-risk compared with low-risk participants. Using DXA, femoral neck areal bone density was 9.4% lower in at-risk compared with low-risk participants (p = 0.005). At-risk male participants had 21.9% lower femoral neck areal bone density (via DXA) than low-risk males (p = 0.020) with no significant differences in females. Overall, 33.3% of athletes were at-risk for REDs and had lower bone quality than those at low-risk.

Review of the scientific rationale, development and validation of the International Olympic Committee Relative Energy Deficiency in Sport Clinical Assessment Tool: V.2 (IOC REDs CAT2)-by a subgroup of the IOC consensus on REDs

Relative Energy Deficiency in Sport (REDs) has various different risk factors, numerous signs and symptoms and is heavily influenced by one's environment. Accordingly, there is no singular validated diagnostic test. This 2023 International Olympic Committee's REDs Clinical Assessment Tool-V.2 (IOC REDs CAT2) implements a three-step process of: (1) initial screening; (2) severity/risk stratification based on any identified REDs signs/symptoms (primary and secondary indicators) and (3) a physician-led final diagnosis and treatment plan developed with the athlete, coach and their entire health and performance team. The CAT2 also introduces a more clinically nuanced four-level traffic-light (green, yellow, orange and red) severity/risk stratification with associated sport participation guidelines. Various REDs primary and secondary indicators have been identified and 'weighted' in terms of scientific support, clinical severity/risk and methodological validity and usability, allowing for objective scoring of athletes based on the presence or absence of each indicator. Early draft versions of the CAT2 were developed with associated athlete-testing, feedback and refinement, followed by REDs expert validation via voting statements (ie, online questionnaire to assess agreement on each indicator). Physician and practitioner validity and usability assessments were also implemented. The aim of the IOC REDs CAT2 is to assist qualified clinical professionals in the early and accurate diagnosis of REDs, with an appropriate clinical severity and risk assessment, in order to protect athlete health and prevent prolonged and irreversible outcomes of REDs.

2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs)

Relative Energy Deficiency in Sport (REDs) was first introduced in 2014 by the International Olympic Committee's expert writing panel, identifying a syndrome of deleterious health and performance outcomes experienced by female and male athletes exposed to low energy availability (LEA; inadequate energy intake in relation to exercise energy expenditure). Since the 2018 REDs consensus, there have been >170 original research publications advancing the field of REDs science, including emerging data demonstrating the growing role of low carbohydrate availability, further evidence of the interplay between mental health and REDs and more data elucidating the impact of LEA in males. Our knowledge of REDs signs and symptoms has resulted in updated Health and Performance Conceptual Models and the development of a novel Physiological Model. This Physiological Model is designed to demonstrate the complexity of either problematic or adaptable LEA exposure, coupled with individual moderating factors, leading to changes in health and performance outcomes. Guidelines for safe and effective body composition assessment to help prevent REDs are also outlined. A new REDs Clinical Assessment Tool-Version 2 is introduced to facilitate the detection and clinical diagnosis of REDs based on accumulated severity and risk stratification, with associated training and competition recommendations. Prevention and treatment principles of REDs are presented to encourage best practices for sports organisations and clinicians. Finally, methodological best practices for REDs research are outlined to stimulate future high-quality research to address important knowledge gaps.

Mapping the complexities of Relative Energy Deficiency in Sport (REDs): development of a physiological model by a subgroup of the International Olympic Committee (IOC) Consensus on REDs

The 2023 International Olympic Committee (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs) notes that exposure to low energy availability (LEA) exists on a continuum between adaptable and problematic LEA, with a range of potential effects on both health and performance. However, there is variability in the outcomes of LEA exposure between and among individuals as well as the specific manifestations of REDs. We outline a framework for a 'systems biology' examination of the effect of LEA on individual body systems, with the eventual goal of creating an integrated map of body system interactions. We provide a template that systematically identifies characteristics of LEA exposure (eg, magnitude, duration, origin) and a variety of moderating factors (eg, medical history, diet and training characteristics) that could exacerbate or attenuate the type and severity of impairments to health and performance faced by an individual athlete. The REDs Physiological Model may assist the diagnosis of underlying causes of problems associated with LEA, with a personalised and nuanced treatment plan promoting compliance and treatment efficacy. It could also be used in the strategic prevention of REDs by drawing attention to scenarios of LEA in which impairments of health and performance are most likely, based on knowledge of the characteristics of the LEA exposure or moderating factors that may increase the risk of harmful outcomes. We challenge researchers and practitioners to create a unifying and dynamic physiological model for each body system that can be continuously updated and mapped as knowledge is gained.

High-impact jumping mitigates the short-term effects of low energy availability on bone resorption but not formation in regularly menstruating females: A randomized control trial

Low energy availability (LEA) is prevalent in active individuals and negatively impacts bone turnover in young females. High-impact exercise can promote bone health in an energy efficient manner and may benefit bone during periods of LEA. Nineteen regularly menstruating females (aged 18-31 years) participated in two three-day conditions providing 15 (LEA) and 45 kcals kg fat-free mass-1  day-1 (BAL) of energy availability, each beginning 3 ± 1 days following the self-reported onset of menses. Participants either did (LEA+J, n = 10) or did not (LEA, n = 9) perform 20 high-impact jumps twice per day during LEA, with P1NP, β-CTx (circulating biomarkers of bone formation and resorption, respectively) and other markers of LEA measured pre and post in a resting and fasted state. Data are presented as estimated marginal mean ± 95% CI. P1NP was significantly reduced in LEA (71.8 ± 6.1-60.4 ± 6.2 ng mL-1 , p < 0.001, d = 2.36) and LEA+J (93.9 ± 13.4-85.2 ± 12.3 ng mL-1 , p < 0.001, d = 1.66), and these effects were not significantly different (time by condition interaction: p = 0.269). β-CTx was significantly increased in LEA (0.39 ± 0.09-0.46 ± 0.10 ng mL-1 , p = 0.002, d = 1.11) but not in LEA+J (0.65 ± 0.08-0.65 ± 0.08 ng mL-1 , p > 0.999, d = 0.19), and these effects were significantly different (time by condition interaction: p = 0.007). Morning basal bone formation rate is reduced following 3 days LEA, induced via dietary restriction, with or without high-impact jumping in regularly menstruating young females. However, high-impact jumping can prevent an increase in morning basal bone resorption rate and may benefit long-term bone health in individuals repeatedly exposed to such bouts.

Low energy availability reduces myofibrillar and sarcoplasmic muscle protein synthesis in trained females

Low energy availability (LEA) describes a state where the energy intake is insufficient to cover the energy costs of both exercise energy expenditure and basal physiological body functions. LEA has been associated with various physiological consequences, such as reproductive dysfunction. However, the effect of LEA on skeletal muscle protein synthesis in females performing exercise training is still poorly understood. We conducted a randomized controlled trial to investigate the impact of LEA on daily integrated myofibrillar and sarcoplasmic muscle protein synthesis in trained females. Thirty eumenorrheic females were matched based on training history and randomized to undergo 10 days of LEA (25 kcal · kg fat-free mass (FFM)-1  · day-1 ) or optimal energy availability (OEA, 50 kcal · kg FFM-1  · day-1 ). Before the intervention, both groups underwent a 5-day 'run-in' period with OEA. All foods were provided throughout the experimental period with a protein content of 2.2 g kg lean mass-1  · day-1 . A standardized, supervised combined resistance and cardiovascular exercise training programme was performed over the experimental period. Daily integrated muscle protein synthesis was measured by deuterium oxide (D2 O) consumption along with changes in body composition, resting metabolic rate, blood biomarkers and 24 h nitrogen balance. We found that LEA reduced daily integrated myofibrillar and sarcoplasmic muscle protein synthesis compared with OEA. Concomitant reductions were observed in lean mass, urinary nitrogen balance, free androgen index, thyroid hormone concentrations and resting metabolic rate following LEA. These results highlight that LEA may negatively affect skeletal muscle adaptations in females performing exercise training. KEY POINTS: Low energy availability (LEA) with potential health and performance impairments is widespread among female athletes. We investigated the impact of 10 days of LEA on daily integrated myofibrillar and sarcoplasmic muscle protein synthesis in young, trained females. We show that LEA impairs myofibrillar and sarcoplasmic muscle protein synthesis in trained females performing exercise training. These findings suggest that LEA may have negative consequences for skeletal muscle adaptations and highlight the importance of ensuring adequate energy availability in female athletes.

Short Severe Energy Restriction with Refueling Reduces Body Mass without Altering Training-Associated Performance Improvement

PURPOSE

We investigated short-term (9 d) exposure to low energy availability (LEA) in elite endurance athletes during a block of intensified training on self-reported well-being, body composition, and performance.

METHODS

Twenty-three highly trained race walkers undertook an ~3-wk research-embedded training camp during which they undertook baseline testing and 6 d of high energy/carbohydrate (HCHO) availability (40 kcal·kg FFM -1 ·d -1 ) before being allocated to 9 d continuation of this diet ( n = 10 M, 2 F) or a significant decrease in energy availability to 15 kcal·kg FFM -1 ·d -1 (LEA: n = 10 M, 1 F). A real-world 10,000-m race walking event was undertaken before (baseline) and after (adaptation) these phases, with races being preceded by standardized carbohydrate fueling (8 g·kg body mass [BM] -1 for 24 h and 2 g·kg BM -1 prerace meal).

RESULTS

Dual-energy x-ray absorptiometry-assessed body composition showed BM loss (2.0 kg, P < 0.001), primarily due to a 1.6-kg fat mass reduction ( P < 0.001) in LEA, with smaller losses (BM = 0.9 kg, P = 0.008; fat mass = 0.9 kg, P < 0.001) in HCHO. The 76-item Recovery-Stress Questionnaire for Athletes, undertaken at the end of each dietary phase, showed significant diet-trial effects for overall stress ( P = 0.021), overall recovery ( P = 0.024), sport-specific stress ( P = 0.003), and sport-specific recovery ( P = 0.012). However, improvements in race performance were similar: 4.5% ± 4.1% and 3.5% ± 1.8% for HCHO and LEA, respectively ( P < 0.001). The relationship between changes in performance and prerace BM was not significant ( r = -0.08 [-0.49 to 0.35], P = 0.717).

CONCLUSIONS

A series of strategically timed but brief phases of substantially restricted energy availability might achieve ideal race weight as part of a long-term periodization of physique by high-performance athletes, but the relationship between BM, training quality, and performance in weight-dependent endurance sports is complicated.

Physiology of Health and Performance: Enabling Success of Women in Combat Arms Roles

INTRODUCTION

The modern female soldier has yet to be fully characterized as she steps up to fill new combat roles that have only recently been opened to women. Both U.S. and U.K. military operational research efforts are supporting a science-based evolution of physical training and standards for female warfighters. The increasing representation of women in all military occupations makes it possible to discover and document the limits of female physiological performance.

METHOD

An informal Delphi process was used to synthesize an integrated concept of current military female physiological research priorities and emerging findings using a panel of subject matter experts who presented their research and perspectives during the second Women in Combat Summit hosted by the TriService Nursing Research Program in February 2021.

RESULTS

The physical characteristics of the modern soldier are changing as women train for nontraditional military roles, and they are emerging as stronger and leaner. Capabilities and physique will likely continue to evolve in response to new Army standards and training programs designed around science-based sex-neutral requirements. Strong bones may be a feature of the female pioneers who successfully complete training and secure roles traditionally reserved for men. Injury risk can be reduced by smarter, targeted training and with attention directed to female-specific hormonal status, biomechanics, and musculoskeletal architecture. An "estrogen advantage" appears to metabolically support enhanced mental endurance in physically demanding high-stress field conditions; a healthy estrogen environment is also essential for musculoskeletal health. The performance of female soldiers can be further enhanced by attention to equipment that serves their needs with seemingly simple solutions such as a suitable sports bra and personal protective equipment that accommodates the female anatomy.

CONCLUSIONS

Female physiological limits and performance have yet to be adequately defined as women move into new roles that were previously developed and reserved for men. Emerging evidence indicates much greater physical capacity and physiological resilience than previously postulated.

The impact of the menstrual cycle on orthopaedic sports injuries in female athletes

There is a disparity in sport-related injuries between sexes, with females sustaining non-contact musculoskeletal injuries at a higher rate. Anterior cruciate ligament ruptures are between two and eight times more common than in males, and females also have a higher incidence of ankle sprains, patellofemoral pain, and bone stress injuries. The sequelae of such injuries can be devastating to an athlete, resulting in time out of sport, surgery, and the early onset of osteoarthritis. It is important to identify the causes of this disparity and introduce prevention programmes to reduce the incidence of these injuries. A natural difference reflects the effect of reproductive hormones in females, which have receptors in certain musculoskeletal tissues. Relaxin increases ligamentous laxity. Oestrogen decreases the synthesis of collagen and progesterone does the opposite. Insufficient diet and intensive training can lead to menstrual irregularities, which are common in female athletes and result in injury, whereas oral contraception may have a protective effect against certain injuries. It is important for coaches, physiotherapists, nutritionists, doctors, and athletes to be aware of these issues and to implement preventive measures. This annotation explores the relationship between the menstrual cycle and orthopaedic sports injuries in pre-menopausal females, and proposes recommendations to mitigate the risk of sustaining these injuries.

Menstrual Function, Eating Disorders, Low Energy Availability, and Musculoskeletal Injuries in British Servicewomen

PURPOSE

This study aimed to investigate associations between menstrual function, eating disorders, and risk of low energy availability with musculoskeletal injuries in British servicewomen.

METHODS

All women younger than 45 yr in the UK Armed Forces were invited to complete a survey about menstrual function, eating behaviors, exercise behaviors, and injury history.

RESULTS

A total of 3022 women participated; 2% had a bone stress injury in the last 12 months, 20% had ever had a bone stress injury, 40% had a time-loss musculoskeletal injury in the last 12 months, and 11% were medically downgraded for a musculoskeletal injury. Menstrual disturbances (oligomenorrhea/amenorrhea, history of amenorrhea, and delayed menarche) were not associated with injury. Women at high risk of disordered eating (Female Athlete Screening Tool score >94) were at higher risk of history of a bone stress injury (odds ratio (OR; 95% confidence interval (CI)), 2.29 (1.67-3.14); P < 0.001) and time-loss injury in the last 12 months (OR (95% CI), 1.56 (1.21-2.03); P < 0.001) than women at low risk of disordered eating. Women at high risk of low energy availability (Low Energy Availability in Females Questionnaire score ≥8) were at higher risk of bone stress injury in the last 12 months (OR (95% CI), 3.62 (2.07-6.49); P < 0.001), history of a bone stress injury (OR (95% CI), 2.08 (1.66-2.59); P < 0.001), a time-loss injury in the last 12 months (OR (95% CI), 9.69 (7.90-11.9); P < 0.001), and being medically downgraded with an injury (OR (95% CI), 3.78 (2.84-5.04); P < 0.001) than women at low risk of low energy availability.

CONCLUSIONS

Eating disorders and risk of low energy availability provide targets for protecting against musculoskeletal injuries in servicewomen.

Exercise training modifies the bone and endocrine response to graded reductions in energy availability in skeletally mature female rodents

Introduction

Reductions in energy availability leading to weight loss can induce loss of bone and impact important endocrine regulators of bone integrity. We sought to elucidate whether endurance exercise (EX) can mitigate bone loss observed in sedentary (SED) skeletally mature rodents subjected to graded energy deficits.

Methods

Female virgin rats (n=84, 5-mo-old; 12/group) were randomized to baseline controls and either sedentary (SED) or exercise (EX) conditions, and within each exercise status to adlib-fed (ADLIB), or moderate (MOD) or severe (SEV) energy restriction diets for 12 weeks. Rats assigned to EX groups performed treadmill running to increase weekly energy expenditure by 10%. MOD-ER-SED, SEV-ER-SED, MOD-ER-EX and SEV-ER-EX were fed modified AIN93M diets with 20%, 40% 10%, and 30% less energy content, respectively, with 100% of all other nutrients provided.

Results

Energy availability (EA) was effectively reduced by ~14% and ~30% in the MOD-ER and SEV-ER groups, respectively. MOD-ER for 12 weeks resulted in few negative impacts on bone and, except for serum leptin in MOD-ER-SED rats, no significant changes in endocrine factors. By contrast, SEV-ER in SED rats resulted in significantly lower total body and femoral neck bone mass, and reduced serum estradiol, IGF-1 and leptin. EX rats experiencing the same reduction in energy availability as SEV-ER-SED exhibited higher total body mass, lean mass, total BMC, and higher serum IGF-1 at the end of 12 weeks. Bone mechanical properties at 3 bone sites (mid-femur, distal femur, femoral neck) were minimally impacted by ER but positively affected by EX.

Discussion

These findings indicate that combining increased EX energy expenditure with smaller reductions in energy intake to achieve a targeted reduction in EA provides some protection against loss of bone mass and lean mass in skeletally mature female rats, likely due to better preservation of circulating IGF-1, and that bone mechanical integrity is not significantly degraded with either moderate or severe reduced EA.

Healthy Runner Project: a 7-year, multisite nutrition education intervention to reduce bone stress injury incidence in collegiate distance runners

Objectives

We evaluated the effect of a nutrition education intervention on bone stress injury (BSI) incidence among female distance runners at two NCAA Division I institutions.

Methods

Historical BSI rates were measured retrospectively (2010-2013); runners were then followed prospectively in pilot (2013-2016) and intervention (2016-2020) phases. The primary aim was to compare BSI rates in the historical and intervention phases. Pilot phase data are included only for descriptive purposes. The intervention comprised team nutrition presentations focused on optimising energy availability plus individualised nutrition sessions for runners with elevated Female Athlete Triad risk. Annual BSI rates were calculated using a generalised estimating equation Poisson regression model adjusted for age and institution. Post hoc analyses were stratified by institution and BSI type (trabecular-rich or cortical-rich).

Results

The historical phase included 56 runners and 90.2 person-years; the intervention phase included 78 runners and 137.3 person-years. Overall BSI rates were not reduced from the historical (0.52 events per person-year) to the intervention (0.43 events per person-year) phase. Post hoc analyses demonstrated trabecular-rich BSI rates dropped significantly from 0.18 to 0.10 events per person-year from the historical to intervention phase (p=0.047). There was a significant interaction between phase and institution (p=0.009). At Institution 1, the overall BSI rate dropped from 0.63 to 0.27 events per person-year from the historical to intervention phase (p=0.041), whereas no decline was observed at Institution 2.

Conclusion

Our findings suggest that a nutrition intervention emphasising energy availability may preferentially impact trabecular-rich BSI and depend on team environment, culture and resources.

Support for inadvertent undereating in female adolescent athletes with clinical indicators of low energy availability

OBJECTIVES

This study evaluated pathways to low energy availability in a sample of female adolescent athletes (n = 464).

DESIGN

Cross-sectional.

METHODS

Participants (age 13-18 y) underwent assessments for height, weight, eating attitudes and behaviors, and menstrual function. Bone mineral density and body composition were evaluated by dual-energy x-ray absorptiometry in a subset of participants (n = 209). Athletes were classified with clinical indicators of low energy availability if they met criteria for 1) primary or secondary amenorrhea or 2) clinical underweight status (body mass index-for-age < 5th percentile). Disordered eating was assessed using the Eating Disorder Examination Questionnaire.

RESULTS

Thirty (6.5%) athletes exhibited clinical indicators of low energy availability, with higher estimates in leanness than non-leanness sports (10.9% vs. 2.1%, p < 0.005). Among athletes with clinical indicators of low energy availability, 80% (n = 24) did not meet criteria for disordered eating, eating disorder, or report the desire to lose weight. Athletes with (vs. without) clinical indicators of low energy availability exhibited lower lumbar spine (-1.30 ± 1.38 vs. -0.07 ± 1.21, p < 0.001) and total body (-0.30 ± 0.98 vs. 0.53 ± 0.97, p < 0.006) bone mineral density Z-scores.

CONCLUSIONS

A majority of female adolescent athletes with clinical indicators of low energy availability did not exhibit characteristics consistent with intentional dietary restriction, supporting the significance of the inadvertent pathway to low energy availability and need for increased nutrition education in this population.

Current risks factors and emerging biomarkers for bone stress injuries in military personnel

INTRODUCTION

Bone stress injuries (BSIs) have plagued the military for over 150 years; they afflict around 5 to 10% of military recruits, more so in women, and continue to place a medical and financial burden on defence. While the tibia generally adapts to the rigours of basic military training, the putative mechanisms for bone maladaptation are still unclear.

METHODS

This paper provides a review of the published literature on current risk factors and emerging biomarkers for BSIs in military personnel; the potential for biochemical markers of bone metabolism to monitor the response to military training; and, the association of novel biochemical 'exerkines' with bone health.

RESULTS

The primary risk factor for BSI in military (and athletic) populations is too much training, too soon. Appropriate physical preparation before training will likely be most protective, but routine biomarkers will not yet identify those at risk. Nutritional interventions will support a bone anabolic response to training, but exposure to stress, sleep loss, and medication is likely harmful to bone. Monitoring physiology using wearables-ovulation, sleep and stress-offer potential to inform prevention strategies.

CONCLUSIONS

The risk factors for BSIs are well described, but their aetiology is very complex particularly in the multi-stressor military environment. Our understanding of the skeletal responses to military training is improving as technology advances, and potential biomarkers are constantly emerging, but sophisticated and integrated approaches to prevention of BSI are warranted.

Identifying latent classes of Relative Energy Deficiency in Sport (RED-S) consequences in a sample of collegiate female cross country runners

OBJECTIVE

The purpose of this study was to identify patterns of clustering of the 10 health consequences identified in the Relative Energy Deficiency in Sport (RED-S) framework among collegiate female Cross-Country runners. We also assessed risk characteristics associated with each cluster.

METHODS

This randomly sampled population included 211 current National Collegiate Athletics Association (NCAA) Division I (DI) female cross country runners who completed a quantitative survey. We used latent class analysis (LCA) to group athletes into mutually exclusive classes based on shared response patterns of RED-S consequences. We computed descriptive statistics to identify demographics, personal characteristics, disordered eating and emotional health characteristics associated with each class.

RESULTS

The average age of the sample was 21 years with mean body mass index 20.4 kg/m². The LCA identified three unique classes of potential RED-S presentations: (1) low probability of RED-S consequences; (2) complex physical and psychological concerns with a higher burden of cardiovascular concern and (3) very high probability of anxiety with high burden of menstrual disturbance, bone injury and gastrointestinal concern. All classes were characterised by high levels of menstrual disturbance and distinguished by the number and burden of other potential RED-S consequences and in reported abuse history, emotional regulation and perfectionism.

CONCLUSION

This study identified a high burden of menstrual disturbance in NCAA D1 cross country runners, and three unique presentations of RED-S consequences. Future research is warranted to better understand how early prevention and intervention strategies may mitigate RED-S consequences in distance runners.

Distribution and risk factors for stress fractures in competitive figure skaters and association with acute fractures

INTRODUCTION

Figure skating combines esthetic components with high impact, technically demanding elements requiring high volume repetitive training. The evidence base for the sport is limited, particularly regarding stress fracture injuries. This study aims to describe the prevalence and anatomical distribution of stress fracture injuries and assess for risk factors, as well as associations with acute fractures.

METHODS

An online anonymous retrospective survey of competitive figure skaters was distributed through social media networks and e-mail for completion by skaters from all three disciplines of figure skating.

RESULTS

In a sample of 164 skaters from novice to Olympic level, career prevalence of stress fractures was 24.4%, most commonly affecting tibia and ankle. There was statistically significant increased risk of stress fracture in those training ≥12 times/week (33.3% vs. 17.8%; P = 0.028) but no increased risk associated with level or gender of skater. There was a higher prevalence of acute fracture in those with a history of stress fracture (45.0% vs. 21.8%; P = 0.007).

CONCLUSIONS

Figure skaters are at a high risk of stress fractures, independent of the level performed at. There is a higher risk in those training more frequently and an association with additional acute fractures. Results advocate education on fracture features and bone health measures to skaters, coaches, and physicians, at all levels of the sport to facilitate early diagnosis and management.