Muscle Glycogen Content during Endurance Training under Low Energy Availability

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.

Energy availability modulates regional blood flow via estrogen-independent pathways in regularly menstruating young women

PURPOSE

This study aimed to investigate the impact of short-term low energy availability (LEA) on vascular function in young, regularly menstruating women.

METHODS

Participants were 19 women, aged 22.9 ± 4.2 years, with body mass index 18-30 kg·m2. They were divided into two groups and completed two conditions in a crossover design: a 3-day control condition (CON) with an energy availability of 45 kcals·kgFFM-1·day-1 and a 3-day LEA condition of 15 kcals·kgFFM-1 day-1. Assessments were conducted during the early follicular phase of the menstrual cycle. Outcome measures included forearm blood flow (FBF), heart rate, blood pressure, arterial stiffness, resting energy expenditure (REE), metabolic blood markers and body composition.

RESULTS

Significant time-by-condition interactions were found for resting FBF (p = .004), REE (p = .042), triiodothyronine (p = .006), β-hydroxybutyrate (p = .002) and body mass (p < .001). Resting FBF was 1.43 ± 1.01 and 1.31 ± 0.61 (arbitrary units) at pre and post, respectively, in LEA and 1.52 ± 0.7 and 1.76 ± 0.57 at pre and post in CON. The LEA condition led to a decrease in triiodothyronine (pre: 1.54 ± 0.28, post: 1.29 ± 0.27 ng ml-1), REE (pre: 1588 ± 165, post: 1487 ± 160 kcals day-1) and body mass (pre: 61.4 ± 7.5, post: 59.6 ± 7.3 kg). Changes in resting FBF were significantly correlated with changes in REE in the LEA condition (r = 0.53; p = 0.02).

CONCLUSION

Short-term LEA modifies regional blood flow and this might contribute to the observed decreased in REE. Findings emphasize the need for careful management of energy availability in populations at risk of LEA.

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).

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.

Association between Low Energy Availability (LEA) and Impaired Sleep Quality in Young Rugby Players

Low energy availability (LEA) has been associated with several physiological consequences, but its impact on sleep has not been sufficiently investigated, especially in the context of young athletes. This study examined the potential association between energy availability (EA) status and objective sleep quality in 42 male rugby players (mean age: 16.2 ± 0.8 years) during a 7-day follow-up with fixed sleep schedules in the midst of an intensive training phase. Participants' energy intake was weighed and recorded. Exercise expenditure was estimated using accelerometry. Portable polysomnography devices captured sleep on the last night of the follow-up. Mean EA was 29.3 ± 9.14 kcal·kg FFM-1·day-1, with 47.6% of athletes presenting LEA, 35.7% Reduced Energy Availability (REA), and 16.7% Optimal Energy Availability (OEA). Lower sleep efficiency (SE) and N3 stage proportion, along with higher wake after sleep onset (WASO), were found in participants with LEA compared to those with OEA (p = 0.04, p = 0.03 and p = 0.005, respectively, with large effect sizes). Segmented regression models of the EA-sleep outcomes (SE, sleep onset latency [SOL]), WASO and N3) relationships displayed two separate linear regions and produced a best fit with a breakpoint between 21-33 kcal·kg FFM-1·day-1. Below these thresholds, sleep quality declines considerably. It is imperative for athletic administrators, nutritionists, and coaches to conscientiously consider the potential impact of LEA on young athletes' sleep, especially during periods of heavy training.

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.

Considerations of Low Carbohydrate Availability (LCA) to Relative Energy Deficiency in Sport (RED-S) in Female Endurance Athletes: A Narrative Review

The purpose of this narrative review is to identify health and performance consequences associated with LCA in female endurance athletes. The intake of carbohydrates (CHO) before, during, and after exercise has been demonstrated to support sport performance, especially endurance activities which rely extensively on CHO as a fuel source. However, low energy availability (LEA) and low carbohydrate availability (LCA) are common in female athletes. LEA occurs when energy intake is insufficient compared to exercise energy expenditure, and LEA-related conditions (e.g., Female Athlete Triad (Triad) and Relative Energy Deficiency in Sport (RED-S)) are associated with a myriad of health and performance consequences. The RED-S model highlights 10 health consequences and 10 performance consequences related to LEA. The independent effect of LCA on health and performance has been under-researched, despite current CHO intake being commonly insufficient in athletes. It is proposed that LCA may not only contribute to LEA but also have independent health and performance consequences in athletes. Furthermore, this review highlights current recommendations for CHO intake, as well as recent data on LCA prevalence and menstrual cycle considerations. A literature review was conducted on PubMed, Science Direct, and ResearchGate using relevant search terms (i.e., "low carbohydrate/energy availability", "female distance runners"). Twenty-one articles were identified and twelve met the inclusion criteria. The total number of articles included in this review is 12, with 7 studies illustrating that LCA was associated with direct negative health and/or performance implications for endurance-based athletes. Several studies included assessed male athletes only, and no studies included a female-only study design. Overall, the cumulative data show that female athletes remain underrepresented in sports science research and that current CHO intake recommendations and strategies may fail to consider female-specific adaptations and hormone responses, such as monthly fluctuations in estrogen and progesterone throughout the menstrual cycle. Current CHO guidelines for female athletes and exercising women need to be audited and explored further in the literature to support female athlete health and performance.

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.

Methodology for studying Relative Energy Deficiency in Sport (REDs): a narrative review by a subgroup of the International Olympic Committee (IOC) consensus on REDs

In the past decade, the study of relationships among nutrition, exercise and the effects on health and athletic performance, has substantially increased. The 2014 introduction of Relative Energy Deficiency in Sport (REDs) prompted sports scientists and clinicians to investigate these relationships in more populations and with more outcomes than had been previously pursued in mostly white, adolescent or young adult, female athletes. Much of the existing physiology and concepts, however, are either based on or extrapolated from limited studies, and the comparison of studies is hindered by the lack of standardised protocols. In this review, we have evaluated and outlined current best practice methodologies to study REDs in an attempt to guide future research.This includes an agreement on the definition of key terms, a summary of study designs with appropriate applications, descriptions of best practices for blood collection and assessment and a description of methods used to assess specific REDs sequelae, stratified as either Preferred, Used and Recommended or Potential Researchers can use the compiled information herein when planning studies to more consistently select the proper tools to investigate their domain of interest. Thus, the goal of this review is to standardise REDs research methods to strengthen future studies and improve REDs prevention, diagnosis and care.

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.

Exogenous glucose oxidation during endurance exercise under low energy availability

The present study was conducted to determine the effect of endurance exercise under low energy availability (EA) on exogenous glucose oxidation during endurance exercise. Ten active males (21.4 ± 0.6 years, 170.4 ± 1.4 cm, 62.4 ± 1.5 kg, 21.5 ± 0.4 kg/m²) completed two trials, consisting of two consecutive days (days 1 and 2) of endurance training under low EA (19.9 ± 0.2 kcal/kg fat free mass [FFM]/day, LEA trial) or normal EA (46.4 ± 0.1 kcal/kg FFM/day, NEA trial). The order of these two trials was randomized with at least a 1-week interval between trials. As an endurance training, participants performed 60 min of treadmill running at 70% of maximal oxygen uptake (V˙O2max) during two consecutive days (on days 1 and 2). On day 1, the endurance training was performed with consumed individually manipulated meals. During the endurance exercise on day 2, exogenous glucose oxidation was evaluated using ¹³C-labeled glucose, and respiratory gas samples were collected. In addition, blood glucose and lactate concentrations were measured immediately after exercise on day 2. Body composition, blood parameters, and resting respiratory gas variables were evaluated under overnight fasting on days 1 and 2. Body weight was significantly reduced in the LEA trial on day2 (day1: 61.8 ± 1.4 kg, day 2: 61.3 ± 1.4 kg, P < 0.001). There were no significant differences between trials in ¹³C excretion (P = 0.33) and area under the curve during the 60 min of exercise (LEA trial: 40.4 ± 3.1 mmol•60min, NEA trial: 40.4 ± 3.1 mmol•60min, P = 0.99). However, the respiratory exchange ratio (RER, LEA trial: 0.88 ± 0.01, NEA trial: 0.90 ± 0.01) and carbohydrate oxidation (LEA trial: 120.1 ± 8.8 g, NEA trial: 136.8 ± 8.6 g) during endurance exercise showed significantly lower values in the LEA trial than in the NEA trial (P = 0.01 for RER and carbohydrate oxidation). Serum insulin and total ketone body concentrations were significantly changed after a day of endurance training under low EA (P = 0.04 for insulin, P < 0.01 for total ketone). In conclusion, low EA during endurance exercise reduced systemic carbohydrate oxidation; however, exogenous glucose oxidation (evaluated by ¹³C excretion) remained unchanged during exercise under low EA.

Markers of Low Energy Availability in Overreached Athletes: A Systematic Review and Meta-analysis

BACKGROUND

Overreaching is the transient reduction in performance that occurs following training overload and is driven by an imbalance between stress and recovery. Low energy availability (LEA) may drive underperformance by compounding training stress; however, this has yet to be investigated systematically.

OBJECTIVE

The aim of this study was to quantify changes in markers of LEA in athletes who demonstrated underperformance, and exercise performance in athletes with markers of LEA.

METHODS

Studies using a ≥ 2-week training block with maintained or increased training loads that measured exercise performance and markers of LEA were identified using a systematic search following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Changes from pre- to post-training were analyzed for (1) markers of LEA in underperforming athletes and (2) performance in athletes with ≥ 2 markers of LEA.

RESULTS

From 56 identified studies, 14 separate groups of athletes demonstrated underperformance, with 50% also displaying ≥ 2 markers of LEA post-training. Eleven groups demonstrated ≥ 2 markers of LEA independent of underperformance and 37 had no performance reduction or ≥ 2 markers of LEA. In underperforming athletes, fat mass (d =  - 0.29, 95% confidence interval [CI] - 0.54 to - 0.04; p = 0.02), resting metabolic rate (d =  - 0.63, 95% CI - 1.22 to - 0.05; p = 0.03), and leptin (d =  - 0.72, 95% CI - 1.08 to - 0.35; p < 0.0001) were decreased, whereas body mass (d =  - 0.04, 95% CI - 0.21 to 0.14; p = 0.70), cortisol (d =  - 0.06, 95% CI - 0.35 to 0.23; p = 0.68), insulin (d =  - 0.12, 95% CI - 0.43 to 0.19; p = 0.46), and testosterone (d =  - 0.31, 95% CI - 0.69 to 0.08; p = 0.12) were unaltered. In athletes with ≥ 2 LEA markers, performance was unaffected (d = 0.09, 95% CI - 0.30 to 0.49; p = 0.6), and the high heterogeneity in performance outcomes (I² = 84.86%) could not be explained by the performance tests used or the length of the training block.

CONCLUSION

Underperforming athletes may present with markers of LEA, but overreaching is also observed in the absence of LEA. The lack of a specific effect and high variability of outcomes with LEA on performance suggests that LEA is not obligatory for underperformance.

A Life History Perspective on Athletes with Low Energy Availability

The energy costs of athletic training can be substantial, and deficits arising from costs unmet by adequate energy intake, leading to a state of low energy availability, may adversely impact athlete health and performance. Life history theory is a branch of evolutionary theory that recognizes that the way the body uses energy-and responds to low energy availability-is an evolved trait. Energy is a finite resource that must be distributed throughout the body to simultaneously fuel all biological processes. When energy availability is low, insufficient energy may be available to equally support all processes. As energy used for one function cannot be used for others, energetic "trade-offs" will arise. Biological processes offering the greatest immediate survival value will be protected, even if this results in energy being diverted away from others, potentially leading to their downregulation. Athletes with low energy availability provide a useful model for anthropologists investigating the biological trade-offs that occur when energy is scarce, while the broader conceptual framework provided by life history theory may be useful to sport and exercise researchers who investigate the influence of low energy availability on athlete health and performance. The goals of this review are: (1) to describe the core tenets of life history theory; (2) consider trade-offs that might occur in athletes with low energy availability in the context of four broad biological areas: reproduction, somatic maintenance, growth, and immunity; and (3) use this evolutionary perspective to consider potential directions for future research.

Collegiate Male Athletes Exhibit Conditions of the Male Athlete Triad

The primary purpose of this study was to determine prevalence of the Male Athlete Triad (MAT) conditions: low energy availability (EA), low bone mineral density (BMD), and low testosterone in male collegiate athletes from different sports. Participants included 44 collegiate male athletes (age, 20.4 ± 0.2 yr; BMI, 25.3 ± 1.3 kg/m2) from seven sports (cross country, soccer, basketball, wrestling, track, golf, and baseball). Resting metabolic rate, three-day food intake, seven-day exercise energy expenditure, body composition, and reproductive and metabolic hormones were assessed. Of the total participants, 15% had low EA, 0% had low BMD, 28% had low total testosterone (TT), and 80% had low calculated free testosterone (cFT). There were no significant correlations between EA, BMD, TT, and cFT. Insulin and sex hormone binding globulin (SHBG) were below and on the upper end of the reference range for healthy male adults, respectively. Insulin was negatively correlated with total (r = -0.330, p = 0.043) and lumbar spine BMD z-scores (r = -0.413, p = 0.010). Low TT and low cFT were the most prevalent MAT conditions among all athletes. Further research should investigate the relationship between insulin and SHBG and the role of these hormones in the MAT. Novelty Bullets • Assessment of energy availability alone is not sufficient to identify physiological disturbances in collegiate male athletes. • Low total and/or free testosterone may be present in some collegiate male athletes, regardless of BMD status. • Low insulin and high SHBG concentration may portray the presence of conditions of the MAT in male collegiate athletes.

Prevalence of Surrogate Markers of Relative Energy Deficiency in Male Norwegian Olympic-Level Athletes

The syndrome of Relative Energy Deficiency in Sport (RED-S) includes wide-ranging effects on physiological and psychological functioning, performance, and general health. However, RED-S is understudied among male athletes at the highest performance levels. This cross-sectional study aimed to investigate surrogate RED-S markers prevalence in Norwegian male Olympic-level athletes. Athletes (n = 44) aged 24.7 ± 3.8 years, body mass 81.3 ± 15.9 kg, body fat 13.7% ± 5.8%, and training volume 76.1 ± 22.9 hr/month were included. Assessed parameters included resting metabolic rate (RMR), body composition, and bone mineral density by dual-energy X-ray absorptiometry and venous blood variables (testosterone, free triiodothyronine, cortisol, and lipids). Seven athletes (16%) grouped by the presence of low RMR (RMRratio < 0.90) (0.81 ± 0.07 vs. 1.04 ± 0.09, p < .001, effect size 2.6), also showed lower testosterone (12.9 ± 5.3 vs. 19.0 ± 5.3 nmol/L, p = .020) than in normal RMR group. In low RMRratio individuals, prevalence of other RED-S markers (-subclinical-low testosterone, low free triiodothyronine, high cortisol, and elevated low-density lipoprotein) was (N/number of markers): 2/0, 2/1, 2/2, 1/3. Low bone mineral density (z-score < -1) was found in 16% of the athletes, all with normal RMR. Subclinical low testosterone and free triiodothyronine levels were found in nine (25%) and two (5%) athletes, respectively. Subclinical high cortisol was found in 23% of athletes while 34% had elevated low-density lipoprotein cholesterol levels. Seven of 12 athletes with two or more RED-S markers had normal RMR. In conclusion, this study found that multiple RED-S markers also exist in male Olympic-level athletes. This highlights the importance of regular screening of male elite athletes, to ensure early detection and treatment of RED-S.

Nutritional Risks among Adolescent Athletes with Disordered Eating

In their attempt to achieve the optimum weight or body shape for their activity, athletes frequently use harmful weight-control practices that may lead to the development of disordered eating or eating disorders. These practices are linked to several medical and mental consequences that may be more serious in adolescent athletes, as their bodies must meet both intensive growth demands and training requirements at the same time. Among other consequences, adolescent athletes may be at nutritional risk, due to their high nutrient needs and unhealthy eating behaviors. A literature review was conducted to examine the main nutritional risks and malnutrition issues faced by adolescent athletes that present disordered eating attitudes or eating disorders. Most studies refer to adult elite athletes, however research on adolescent athletes also indicates that the most common nutritional risks that may arise due to disordered eating include energy, macronutrient and micronutrient deficiencies, dehydration and electrolyte imbalances and changes in body composition that may lead to menstrual abnormalities, and decreased bone mass density. Educational programs and early detection of disordered eating and eating disorders are crucial to avoid the emergence and ensure timely management of nutrition-related problems in the vulnerable group of adolescent athletes.

Overtraining Syndrome (OTS) and Relative Energy Deficiency in Sport (RED-S): Shared Pathways, Symptoms and Complexities

The symptom similarities between training-overload (with or without an Overtraining Syndrome (OTS) diagnosis) and Relative Energy Deficiency in Sport (RED-S) are significant, with both initiating from a hypothalamic-pituitary origin, that can be influenced by low carbohydrate (CHO) and energy availability (EA). In this narrative review we wish to showcase that many of the negative outcomes of training-overload (with, or without an OTS diagnosis) may be primarily due to misdiagnosed under-fueling, or RED-S, via low EA and/or low CHO availability. Accordingly, we undertook an analysis of training-overload/OTS type studies that have also collected and analyzed for energy intake (EI), CHO, exercise energy expenditure (EEE) and/or EA. Eighteen of the 21 studies (86%) that met our criteria showed indications of an EA decrease or difference between two cohorts within a given study (n = 14 studies) or CHO availability decrease (n = 4 studies) during the training-overload/OTS period, resulting in both training-overload/OTS and RED-S symptom outcomes compared to control conditions. Furthermore, we demonstrate significantly similar symptom overlaps across much of the OTS (n = 57 studies) and RED-S/Female Athlete Triad (n = 88 studies) literature. It is important to note that the prevention of under-recovery is multi-factorial, but many aspects are based around EA and CHO availability. Herein we have demonstrated that OTS and RED-S have many shared pathways, symptoms, and diagnostic complexities. Substantial attention is required to increase the knowledge and awareness of RED-S, and to enhance the diagnostic accuracy of both OTS and RED-S, to allow clinicians to more accurately exclude LEA/RED-S from OTS diagnoses.

Hepcidin response to three consecutive days of endurance training in hypoxia

PURPOSE

The purpose of this study was to determine the effects of 3 consecutive days of endurance training in hypoxia on hepcidin responses.

METHOD

Nine active healthy males completed two trials, consisting of 3 consecutive days of endurance training in either hypoxia [fraction of inspired oxygen (F_iO₂): 14.5%) or normoxia (F_iO₂: 20.9%). On days 1-3, participants performed one 90 min session of endurance training per day, consisting of high-intensity endurance interval exercise [10 × 4 min of pedaling at 80% of maximal oxygen uptake ([Formula: see text]O_2max) with 2 min of active rest at 30% of [Formula: see text]O_2max] followed by 30 min of continuous exercise at 60% of [Formula: see text]O_2max. Venous blood samples were collected prior to exercise each day during the experimental period (days 1-4) to determine serum hepcidin, iron, ferritin, haptoglobin, and ketone body concentrations.

RESULT

Serum iron (p < 0.0001), ferritin (p = 0.005) and ketone body (p < 0.0001) concentrations increased significantly in both trials on days 2-4 compared with day 1, with no significant differences between trials. No significant changes in serum haptoglobin concentrations were observed throughout the experimental period in either trial. Serum hepcidin concentrations also increased significantly on days 2-4 compared with day 1 in both trials (p = 0.004), with no significant differences observed between trials.

CONCLUSION

3 consecutive days of endurance training in hypoxia did not affect hepcidin concentrations compared with endurance training in normoxia.

Low energy availability: history, definition and evidence of its endocrine, metabolic and physiological effects in prospective studies in females and males

Energy availability (EA) is defined as the amount of dietary energy available to sustain physiological function after subtracting the energetic cost of exercise. Insufficient EA due to increased exercise, reduced energy intake, or a combination of both, is a potent disruptor of the endocrine milieu. As such, EA is conceived as a key etiological factor underlying a plethora of physiological dysregulations described in the female athlete triad, its male counterpart and the Relative Energy Deficiency in Sport models. Originally developed upon female-specific physiological responses, this concept has recently been extended to males, where experimental evidence is limited. The majority of data for all these models are from cross-sectional or observational studies where hypothesized chronic low energy availability (LEA) is linked to physiological maladaptation. However, the body of evidence determining causal effects of LEA on endocrine, and physiological function through prospective studies manipulating EA is comparatively small, with interventions typically lasting ≤ 5 days. Extending laboratory-based findings to the field requires recognition of the strengths and limitations of current knowledge. To aid this, this review will: (1) provide a brief historical overview of the origin of the concept in mammalian ecology through its evolution of algebraic calculations used in humans today, (2) Outline key differences from the ‘energy balance’ concept, (3) summarise and critically evaluate the effects of LEA on tissues/systems for which we now have evidence, namely: hormonal milieu, reproductive system endocrinology, bone metabolism and skeletal muscle; and finally (4) provide perspectives and suggestions for research upon identified knowledge gaps.

Reasons for and Consequences of Low Energy Availability in Female and Male Athletes: Social Environment, Adaptations, and Prevention

Low energy availability (LEA) represents a state in which the body does not have enough energy left to support all physiological functions needed to maintain optimal health. When compared to the normal population, athletes are particularly at risk to experience LEA and the reasons for this are manifold. LEA may result from altered dietary behaviours that are caused by body dissatisfaction, the belief that a lower body weight will result in greater performance, or social pressure to look a certain way. Pressure can also be experienced from the coach, teammates, and in this day and age through social media platforms. While LEA has been extensively described in females and female athletes have started fighting against the pressure to be thin using their social media platforms, evidence shows that male athletes are at risk as well. Besides those obvious reasons for LEA, athletes engaging in sports with high energy expenditure (e.g. rowing or cycling) can unintentionally experience LEA; particularly, when the athletes' caloric intake is not matched with exercise intensity. Whether unintentional or not, LEA may have detrimental consequences on health and performance, because both short-term and long-term LEA induces a variety of maladaptations such as endocrine alterations, suppression of the reproductive axis, mental disorders, thyroid suppression, and altered metabolic responses. Therefore, the aim of this review is to increase the understanding of LEA, including the role of an athlete's social environment and the performance effects related to LEA.

Heterogeneity in subcellular muscle glycogen utilisation during exercise impacts endurance capacity in men

KEY POINTS

When muscle biopsies first began to be used routinely in research on exercise physiology five decades ago, it soon become clear that the muscle content of glycogen is an important determinant of exercise performance. Glycogen particles are stored in distinct pools within the muscles, but the role of each pool during exercise and how this is affected by diet is unknown. Here, the effects of diet and exercise on these pools, as well as their relation to endurance during prolonged cycling were examined. We demonstrate here that an improved endurance capacity with high carbohydrate loading is associated with a temporal shift in the utilisation of the distinct stores of glycogen pools and is closely linked to the content of the glycogen pool closest to actin and myosin (intramyofibrillar glycogen). These findings highlight the functional importance of distinguishing between different subcellular microcompartments of glycogen in individual muscle fibres.

ABSTRACT

In muscle cells, glycogen is stored in three distinct subcellular pools: between or within myofibrils (inter- and intramyofibrillar glycogen, respectively) or beneath the sarcolemma (subsarcolemmal glycogen) and these pools may well have different functions. Here, we investigated the effect of diet and exercise on the content of these distinct pools and their relation to endurance capacity in type 1 and 2 muscle fibres. Following consumption of three different diets (normal, mixed diet = MIX, high in carbohydrate = HIGH, or low in carbohydrate = LOW) for 72 h, 11 men cycled at 75% of V ̇ O 2 max until exhaustion. The volumetric content of the glycogen pools in muscle biopsies obtained before, during, and after exercise were quantified by transmission electron micrographs. The mean (SD) time to exhaustion was 150 (30), 112 (22), and 69 (18) minutes in the HIGH, MIX and LOW trials, respectively (P < 0.001). As shown by multiple regression analyses, the intramyofibrillar glycogen content in type 1 fibres, particularly after 60 min of exercise, correlated most strongly with time to exhaustion. In the HIGH trial, intramyofibrillar glycogen was spared during the initial 60 min of exercise, which was associated with levels and utilisation of subsarcolemmal glycogen above normal. In all trials, utilisation of subsarcolemmal and intramyofibrillar glycogen was more pronounced than that of intermyofibrillar glycogen in relative terms. In conclusion, the muscle pool of intramyofibrillar glycogen appears to be the most important for endurance capacity in humans. In addition, a local abundance of subsarcolemmal glycogen reduces the utilisation of intramyofibrillar glycogen during exercise.