Changes in tibial bone microarchitecture in female recruits in response to 8 weeks of U.S. Army Basic Combat Training

Association between changes in serum bone metabolism markers and bone microarchitecture changes during basic combat training - The ARMI study

IMPORTANCE

U.S. Army Basic Combat Training (BCT) improves tibial volumetric bone mineral density (BMD) and structure in most, but not all soldiers. Few studies have investigated whether changes in serum bone biomarkers during BCT are associated with changes in tibial BMD and bone structure following BCT.

OBJECTIVE

To characterize bone biomarker changes during BCT and to investigate the relationship between changes in bone biomarkers and changes in tibial BMD and bone structure.

METHODS

We enrolled 235 trainees entering BCT in this ten-week prospective observational study. Trainees provided fasted blood samples and questionnaires weekly throughout BCT. Procollagen type 1 N-terminal propeptide (PINP) and C-terminal telopeptide of type 1 collagen (CTX) were measured by enzyme-linked immunoabsorbent assays every two weeks during BCT. We evaluated body composition and mass via dual-energy X-ray absorptiometry and bone structure, microarchitecture, and mineral density at the distal tibia via high-resolution peripheral quantitative computed tomography at baseline and post-BCT.

RESULTS

Both male (n = 110) and female trainees (n = 125) were young (20.9 ± 3.7 and 20.7 ± 4.3 years, respectively), with normal to overweight BMIs (25.2 ± 4.1 and 24.2 ± 3.6 kg/m2, respectively). In female trainees, PINP increased during and post-BCT compared to baseline, with the greatest increase in PINP at week four (45.4 % ± 49.6, p < 0.0001), whereas there were no changes in CTX. PINP also increased in male trainees, but only at weeks two and four (21.9 % ± 24.5, p = 0.0027 and 35.9 % ± 35.8, p < 0.0001, respectively). Unlike female trainees, in males, CTX was lower than baseline at weeks four, eight, and post-BCT. The change in PINP from baseline to week four of BCT was positively associated with changes in tibial BMD, Tb.BMD, Tb.Th, Tb.BV/TV, Ct.Th, Ct.Ar, and Ct.Po from the baseline to post-BCT.

CONCLUSION

The bone formation marker PINP increases during U.S. Army BCT, especially during the first four weeks. Increases in PINP, but not CTX, were correlated with improved BMD and bone structure in the distal tibia.

Biomechanical and physiological biomarkers are useful indicators of military personnel readiness: a multi-institutional, multinational research collaboration

A ubiquitous problem facing military organisations is musculoskeletal injury (MSKI) risk identification. Recently, two research groups, each with their own funding, collaborated to address this problem. Combining their respective areas of expertise in biomechanics and physiological biomarkers, the group explored this problem in the laboratory and in the field. They have developed a machine learning model in a US Marine Corps (USMC) officer cadet cohort that identifies MSKI risk from a single jump test, identified a minimum inertial measurement unit sensor array to quantity jump and squat performance and have identified sex differences in overuse, lower-limb injury risk. This machine learning model was able to correctly predict lift to place within 4 kg using a testing data set and less than 1 kg in the training set of data. Such collaborative approaches are encouraged to address complicated research problems. To assemble an effective team, consider forming groups that best complement each other's areas of expertise and prioritise securing separate funding to ensure each group can act independently. By doing this, the group has assessed the suitability and feasibility of various wearable technologies, used machine learning to gain insights into USMC physiological training adaptations, and developed an understanding of MSKI risk profiles within this cohort.

Urinary Proteomic Biomarkers of Trabecular Bone Volume Change during Army Basic Combat Training

PURPOSE

The purpose of this study is to optimize a dMS-based urinary proteomic technique and evaluate the relationship between urinary proteome content and adaptive changes in bone microarchitecture during BCT.

METHODS

Urinary proteomes were analyzed with an optimized dMS technique in two groups of 13 recruits ( N = 26) at the beginning (Pre) and end (Post) of BCT. Matched by age (21 ± 4 yr), sex (16 W), and baseline tibial trabecular bone volume fractions (Tb.BV/TV), these groups were distinguished by the most substantial (High) and minimal (Low) improvements in Tb.BV/TV. Differential protein expression was analyzed with mixed permutation ANOVA and false discovery proportion-based adjustment for multiple comparisons.

RESULTS

Tibial Tb.BV/TV increased from pre- to post-BCT in High (3.30 ± 1.64%, P < 0.0001) but not Low (-0.35 ± 1.25%, P = 0.4707). The optimized dMS technique identified 10,431 peptides from 1368 protein groups that represented 165 integrative biological processes. Seventy-four urinary proteins changed from pre- to post-BCT ( P = 0.0019), and neutrophil-mediated immunity was the most prominent ontology. Two proteins (immunoglobulin heavy constant gamma 4 and C-type lectin domain family 4 member G) differed from pre- to post-BCT in High and Low ( P = 0.0006).

CONCLUSIONS

The dMS technique can identify more than 1000 urinary proteins. At least 74 proteins are responsive to BCT, and other principally immune system-related proteins show differential expression patterns that coincide with adaptive bone formation.

Trabecular bone structure of the proximal capitate in extant hominids and fossil hominins with implications for midcarpal joint loading and the dart-thrower's motion

OBJECTIVES

This research examines whether the distribution of trabecular bone in the proximal capitates of extant hominids, as well as several fossil hominin taxa, is associated with the oblique path of the midcarpal joint known as the dart-thrower's motion (DTM).

MATERIALS AND METHODS

We analyzed proximal capitates from extant (Pongo n = 12; Gorilla n = 11; Pan n = 10; fossil and recent Homo sapiens n = 29) and extinct (Australopithecus sediba n = 2; Homo naledi n = 1; Homo floresiensis n = 2; Neandertals n = 3) hominids using a new canonical holistic morphometric analysis, which quantifies and visualizes the distribution of trabecular bone using relative bone volume as a fraction of total volume (rBV/TV).

RESULTS

Homo sapiens and Neandertals had a continuous band of high rBV/TV that extended across the scaphoid, lunate, and hamate subarticular regions, but other fossil hominins and extant great apes did not. A. sediba expressed a distinct combination of human-like and Pan-like rBV/TV distribution. Both H. floresiensis and H. naledi had high rBV/TV on the ulnar-side of the capitate but low rBV/TV on the radial-side.

CONCLUSION

The proximal capitates of H. sapiens and Neandertals share a distinctive distribution of trabecular bone that suggests that these two species of Homo regularly load(ed) their midcarpal joints along the full extent of the oblique path of the DTM. The observed pattern in A. sediba suggests that human-like stress at the capito-scaphoid articular surface was combined with Pan-like wrist postures, whereas the patterns in H. floresiensis and H. naledi suggest their midcarpal joints were loaded differently from that of H. sapiens and Neandertals.

Am I big boned? Bone length scaled reference data for HRpQCT measures of the radial and tibial diaphysis in White adults

Cross-sectional size of a long bone shaft influences its mechanical properties. We recently used high-resolution peripheral quantitative computed tomography (HRpQCT) to create reference data for size measures of the radial and tibial diaphyses. However, data did not take into account the impact of bone length. Human bone exhibits relatively isometric allometry whereby cross-sectional area increases proportionally with bone length. The consequence is that taller than average individuals will generally have larger z-scores for bone size outcomes when length is not considered. The goal of the current work was to develop a means of determining whether an individual's cross-sectional bone size is suitable for their bone length. HRpQCT scans performed at 30 % of bone length proximal from the distal end of the radius and tibia were acquired from 1034 White females (age = 18.0 to 85.3 y) and 392 White males (age = 18.4 to 83.6 y). Positive relationships were confirmed between bone length and cross-sectional areas and estimated mechanical properties. Scaling factors were calculated and used to scale HRpQCT outcomes to bone length. Centile curves were generated for both raw and bone length scaled HRpQCT data using the LMS approach. Excel-based calculators are provided to facilitate calculation of z-scores for both raw and bone length scaled HRpQCT outcomes. The raw z-scores indicate the magnitude that an individual's HRpQCT outcomes differ relative to expected sex- and age-specific values, with the scaled z-scores also considering bone length. The latter enables it to be determined whether an individual or population of interest has normal sized bones for their length, which may have implications for injury risk. In addition to providing a means of expressing HRpQCT bone size outcomes relative to bone length, the current study also provides centile curves for outcomes previously without reference data, including tissue mineral density and moments of inertia.

Advances in the research on myokine-driven regulation of bone metabolism

The traditional view posits that bones and muscles interact primarily through mechanical coupling. However, recent studies have revealed that myokines, proteins secreted by skeletal muscle cells, play a crucial role in the regulation of bone metabolism. Myokines are widely involved in bone metabolism, influencing bone resorption and formation by interacting with factors related to bone cell secretion or influencing bone metabolic pathways. Here, we review the research progress on the myokine regulation of bone metabolism, discuss the mechanism of myokine regulation of bone metabolism, explore the pathophysiological relationship between sarcopenia and osteoporosis, and provide future perspectives on myokine research, with the aim of identify potential specific diagnostic markers and therapeutic entry points.

Utility of HR-pQCT in detecting training-induced changes in healthy adult bone morphology and microstructure

Healthy bone adjusts its traits in an exceptionally coordinated, compensatory process. Recent advancements in skeletal imaging via High-Resolution Peripheral Quantitative Computed Tomography (HR-pQCT) allows for the in vivo 3-dimensional and longitudinal quantification of bone density, microarchitecture, geometry, and parameters of mechanical strength in response to varying strain stimuli including those resulting from exercise or military training. Further, the voxel size of 61 microns has the potential to capture subtle changes in human bone in as little as 8 weeks. Given the typical time course of bone remodeling, short-term detection of skeletal changes in bone microstructure and morphology is indicative of adaptive bone formation, the deposition of new bone formation, uncoupled from prior resorption, that can occur at mechanistically advantageous regions. This review aims to synthesize existing training-induced HR-pQCT data in three distinct populations of healthy adults excluding disease states, pharmacological intervention and nutritional supplementation. Those included are: 1) military basic or officer training 2) general population and 3) non-osteoporotic aging. This review aims to further identify similarities and contrasts with prior modalities and cumulatively interpret results within the scope of bone functional adaptation.

Distal Tibial Bone Properties and Bone Stress Injury Risk in Young Men Undergoing Arduous Physical Training

Trabecular microarchitecture contributes to bone strength, but its role in bone stress injury (BSI) risk in young healthy adults is unclear. Tibial volumetric BMD (vBMD), geometry, and microarchitecture, whole-body areal BMD, lean and fat mass, biochemical markers of bone metabolism, aerobic fitness, and muscle strength and power were measured in 201 British Army male infantry recruits (age 20.7 [4.3] years, BMI 24.0 ± 2.7 kg·m2) in week one of basic training. Tibial scans were performed at the ultra-distal site, 22.5 mm from the distal endplate of the non-dominant leg using High Resolution Peripheral Quantitative Computed Tomography (XtremeCT, Scanco Medical AG, Switzerland). Binary logistic regression analysis was performed to identify associations with lower body BSI confirmed by MRI. 20 recruits (10.0%) were diagnosed with a lower body BSI. Pre-injured participants had lower cortical area, stiffness and estimated failure load (p = 0.029, 0.012 and 0.011 respectively) but tibial vBMD, geometry, and microarchitecture were not associated with BSI incidence when controlling for age, total body mass, lean body mass, height, total 25(OH)D, 2.4-km run time, peak power output and maximum dynamic lift strength. Infantry Regiment (OR 9.3 [95%CI, 2.6, 33.4]) Parachute versus Line Infantry, (p ≤ 0.001) and 2.4-km best effort run time (1.06 [95%CI, 1.02, 1.10], p < 0.033) were significant predictors. Intrinsic risk factors, including ultradistal tibial density, geometry, and microarchitecture, were not associated with lower body BSI during arduous infantry training. The ninefold increased risk of BSI in the Parachute Regiment compared with Line Infantry suggests that injury propensity is primarily a function of training load and risk factors are population-specific.

Non-traditional HIIT-style ROTC training elicits positive bone quality and performance adaptations

Military personnel experience elevated bone injury incidence, partly due to arduous and repetitive training. Non-traditional High-Intensity Interval Training-style (HIIT) may benefit pre-enlisted Reserve Officer Training Corps (ROTC) cadet's musculoskeletal health and performance prior to military service. This study investigated 16 ROTC (n = 12 males; n = 4 females) and 15 physically active sex-, age-, and body mass-matched Controls' musculoskeletal health and performance from November to April. Total body, lumbar spine, and dual- hip dual-energy X-ray absorptiometry scans and 4%, 38%, 66% tibial peripheral quantitative computed tomography scans, blood draws (serum sclerostin and parathyroid hormone), and maximal muscle strength and aerobic capacity testing were completed. From November to April, ROTC improved bone density (DXA) of the dominant total hip and greater trochanter and non-dominant greater trochanter and 38% and 66% tibial total volumetric and cortical bone density (pQCT) similarly or more than Controls (all p ≤ 0.049). From November to April, ROTC also improved bench and leg press, and peak aerobic capacity (all p ≤ 0.013). From November to January, serum sclerostin increased (p ≤ 0.007) and remained elevated through April, while parathyroid hormone was unchanged. HIIT-style training induced positive musculoskeletal adaptations, suggesting it may be an excellent pre-service training modality for this injury prone group.

Is There a Causal Relationship between Physical Activity and Bone Microarchitecture? A Study of Adult Female Twin Pairs

The reasons for the association between physical activity (PA) and bone microarchitecture traits are unclear. We examined whether these associations were consistent with causation and/or with shared familial factors using a cross-sectional study of 47 dizygotic and 93 monozygotic female twin pairs aged 31-77 years. Images of the nondominant distal tibia were obtained using high-resolutionperipheral quantitative computed tomography. The bone microarchitecture was assessed using StrAx1.0 software. Based on a self-completed questionnaire, a PA index was calculated as a weighted sum of weekly hours of light (walking, light gardening), moderate (social tennis, golf, hiking), and vigorous activity (competitive active sports) = light + 2 * moderate + 3 * vigorous. We applied Inference about Causation through Examination of FAmiliaL CONfounding (ICE FALCON) to test whether cross-pair cross-trait associations changed after adjustment for within-individual associations. Within-individual distal tibia cortical cross-sectional area (CSA) and cortical thickness were positively associated with PA (regression coefficients [β] = 0.20 and 0.22), while the porosity of the inner transitional zone was negatively associated with PA (β = -0.17), all p < 0.05. Trabecular volumetric bone mineral density (vBMD) and trabecular thickness were positively associated with PA (β = 0.13 and 0.14), and medullary CSA was negatively associated with PA (β = -0.22), all p ≤ 0.01. Cross-pair cross-trait associations of cortical thickness, cortical CSA, and medullary CSA with PA attenuated after adjustment for the within-individual association (p = 0.048, p = 0.062, and p = 0.028 for changes). In conclusion, increasing PA was associated with thicker cortices, larger cortical area, lower porosity of the inner transitional zone, thicker trabeculae, and smaller medullary cavities. The attenuation of cross-pair cross-trait associations after accounting for the within-individual associations was consistent with PA having a causal effect on the improved cortical and trabecular microarchitecture of adult females, in addition to shared familial factors. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

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.

Hormonal contraceptive use, bone density and biochemical markers of bone metabolism in British Army recruits

INTRODUCTION

Hormonal contraceptive use might impair bone health and increase the risk of stress fracture by decreasing endogenous oestrogen production, a central regulator of bone metabolism. This cross-sectional study investigated bone density and biochemical markers of bone metabolism in women taking hormonal contraceptives on entry to basic military training.

METHODS

Forty-five female British Army recruits had biochemical markers of bone metabolism, areal bone mineral density (aBMD) and tibial speed of sound (tSOS) measured at the start of basic military training. Participants were compared by their method of hormonal contraception: no hormonal contraception (NONE), combined contraceptive pill (CP) or depot-medroxyprogesterone acetate (DMPA) (20±2.8 years, 1.64±0.63 m, 61.7±6.2 kg).

RESULTS

aBMD was not different between groups (p≥0.204), but tSOS was higher in NONE (3%, p=0.014) when compared with DMPA users. Beta C-terminal telopeptide was higher in NONE (45%, p=0.037) and DMPA users (90%, p=0.003) compared with CP users. Procollagen type 1 N-terminal propeptide was higher in DMPA users compared with NONE (43%, p=0.045) and CP users (127%, p=0.001), and higher in NONE compared with CP users (59%, p=0.014). Bone alkaline phosphatase was higher in DMPA users compared with CP users (56%, p=0.044).

CONCLUSIONS

DMPA use was associated with increased bone turnover and decreased cortical bone integrity of the tibia. Lower cortical bone integrity in DMPA users was possibly mediated by increased intracortical remodelling, but trabecular bone was not affected by contraceptive use.

Effect of a physical activity intervention on lower body bone health in childhood cancer survivors: A randomized controlled trial (SURfit)

It remains controversial whether physical activity promotes bone health in childhood cancer survivors (CCS). We aimed to assess the effect of a one-year general exercise intervention on lower body bone parameters of CCS. CCS ≥16 years at enrollment, <16 years at diagnosis and ≥5 years in remission were identified from the national Childhood Cancer Registry. Participants randomized to the intervention group were asked to perform an additional ≥2.5 hours of intense physical activity/week, controls continued exercise as usual. Bone health was assessed as a secondary trial endpoint at baseline and after 12-months. We measured tibia bone mineral density (BMD) and morphology by peripheral quantitative computed tomography and lumbar spine, hip and femoral neck BMD by dual-energy x-ray absorptiometry. We performed intention-to-treat, per protocol, and an explorative subgroup analyses looking at low BMD using multiple linear regressions. One hundred fifty-one survivors (44% females, 7.5 ± 4.9 years at diagnosis, 30.4 ± 8.6 years at baseline) were included. Intention-to-treat analysis revealed no differences in changes between the intervention and control group. Per protocol analyses showed evidence for an improvement in femoral neck and trabecular BMD between 1.5% and 1.8% more in participants being compliant with the exercise program. Trabecular BMD increased 2.8% more in survivors of the intervention group with BMD z-score ≤-1 compared to those starting at z-score >-1. A nonstandardized personalized exercise programs might not be specific enough to promote bone health in CCS, although those compliant and those most in need may benefit. Future trials should include bone stimulating exercise programs targeting risk groups with reduced bone health and motivational features to maximize compliance.

Load carriage aerobic exercise stimulates a transient rise in biochemical markers of bone formation and resorption

Exercise can be both anabolic and catabolic for bone tissue. The temporal response of both bone formation and resorption following an acute bout of exercise is not well described. We assayed biochemical markers of bone and calcium metabolism for up to 3 days after military-relevant exercise. In randomized order, male (n = 18) and female (n = 2) Soldiers (means ± SD; 21.2 ± 4.1 years) performed a 60-min bout of load carriage (30% body mass; 22.4 ± 3.7 kg) treadmill exercise (EXER) or a resting control trial (REST). Blood samples were collected following provision of a standardized breakfast before (PRE), after (POST) exercise/rest, 1 h, 2 h, and 4 h into recovery. Fasted samples were also collected at 0630 on EXER and REST and for the next three mornings after EXER. Parathyroid hormone and phosphorus were elevated (208% and 128% of PRE, respectively, P < 0.05), and ionized calcium reduced (88% of PRE, P < 0.05) after EXER. N-terminal propeptide of type 1 collagen was elevated at POST (111% of PRE, P < 0.05), and the resorption marker, C-terminal propeptide of type 1 collagen was elevated at 1 h (153% of PRE, P < 0.05). Osteocalcin was higher than PRE at 1 through 4 h post EXER (119%-120% of PRE, P < 0.05). Sclerostin and Dickkopf-related protein-1 were elevated only at POST (132% and 121% of PRE, respectively, P < 0.05) during EXER. Trivial changes in biomarkers during successive recovery days were observed. These results suggest that 60 min of load carriage exercise elicits transient increases in bone formation and resorption that return to pre-exercise concentrations within 24 h post-exercise.NEW & NOTEWORTHY In this study, we demonstrated evidence for increases in both bone formation and resorption in the first 4 h after a bout of load carriage exercise. However, these changes largely disappear by 24 h after exercise. Acute formation and resorption of bone following exercise may reflect distinct physiological mechanoadaptive responses. Future work is needed to identify ways to promote acute post-exercise bone formation and minimize post-exercise resorption to optimize bone adaptation to exercise.

Physiological biomarker monitoring during arduous military training: Maintaining readiness and performance

OBJECTIVES

Physiological and psychological stressors can degrade soldiers' readiness and performance during military training and operational environments. Integrative and holistic assessments of biomarkers across diverse human performance optimization domains during multistressor training can be leveraged to provide actionable insight to military leadership regarding service member health and readiness.

DESIGN/METHOD

A broad categorization of biomarkers, to include biochemical measures, bone and body composition, psychometric assessments, movement screening, and physiological load can be incorporated into robust analytical pipelines for understanding the complex factors that impact military human performance.

RESULTS

In this perspective commentary we overview the rationale, selection, and methodologies for monitoring biomarker domains that are relevant to military research and specifically highlight methods that have been incorporated in a research program funded by the Office of Naval Research, Code 34 Biological and Physiological Monitoring and Modeling of Warfighter Performance.

CONCLUSIONS

The integration of screening and continuous monitoring methodologies via robust analytical approaches will provide novel insight for military leaders regarding health, performance, and readiness outcomes during multistressor military training.

Unraveling the physiologic paradoxes that underlie exercise prescription for stress fracture prevention

The effects of exercise on stress fracture risk are paradoxical. Exercise can promote both bone formation and resorption, which in turn, can reduce and increase risk of stress fractures, respectively. We review classic and current literature that suggests that the processes that underlie these responses to exercise are distinct. Bone remodeling involves osteoclastic resorption of fatigue-damaged bone, coupled with subsequent bone deposition to replace the damaged tissue. Bone modeling involves the independent action of osteoblasts and osteoclasts forming or resorbing bone, respectively, on a surface. In the formation mode, modeling results in increased bone stiffness, strength, and resistance to fatigue. Both the remodeling and modeling responses to exercise require significant time for newly deposited bone to fully mineralize. We propose that recognizing these two distinct physiologic pathways and their related time courses reveals the theoretical basis to guide exercise prescription to promote bone health during periods of heightened stress fracture risk. Such guidance may include minimizing rapid increases in the duration of repetitive exercises that may cause fatigue damage accrual, such as long-distance running and marching. Rather, limiting initial exercise characteristics to those known to stimulate bone formation, such as short-duration, moderate-to-high impact, dynamic, and multidirectional activities with rest insertion, may increase the fatigue resistance of bone and consequently minimize stress fracture risk.

Sex differences in tibial adaptations to arduous training: An observational cohort study

Military training increases tibial density and size, but it is unknown if men and women adapt similarly to the same arduous training. Seventy-seven men and 57 women not using hormonal contraceptives completed this study. Tibial volumetric bone mineral density (vBMD) and geometry were measured by peripheral quantitative computed tomography (4%, 14%, 38%, and 66% sites) at the start (week 1) and end (week 14) of British Army basic training. Training increased trabecular vBMD (4% site in men; 4% and 14% sites in women), cortical vBMD (38% site), total area (14% and 38% sites), trabecular area (14% site), cortical area and thickness (14%, 38%, and 66% sites), periosteal perimeter (14%, 38%, and 66% sites), and all indices of estimated strength (14%, 38%, and 66% sites); and, decreased endosteal perimeter (66% site) in men and women (all p ≤ 0.045). The increase in trabecular vBMD (4% and 14% sites) was greater in women and the increases in cortical area and strength (38% site) were greater in men (sex × time interactions, all p ≤ 0.047). P1NP increased and βCTX and sclerostin decreased during training in men and women, consistent with adaptive bone formation. PTH decreased in men but increased in women. Arduous weight-bearing activity increased the density and size of the tibia after 14 weeks. Women experienced similar tibial adaptations as men, however, a greater increase in trabecular vBMD in women compared with men could be due to higher loading at this skeletal site in women, whereas the small increase in cortical area could be due to inhibitory effects of oestradiol.

Investigating the Efficacy of an 18-Week Postpartum Rehabilitation and Physical Development Intervention on Occupational Physical Performance and Musculoskeletal Health in UK Servicewomen: Protocol for an Independent Group Study Design

Background

Postpartum women are at an increased risk of pelvic floor dysfunction, musculoskeletal injury, and poor psychological health and have reduced physical fitness compared to before pregnancy. There is no formal, evidence-based rehabilitation and physical development program for returning UK servicewomen to work following childbirth.

Objective

This study aims to examine the efficacy of a rehabilitation and physical development intervention for returning postpartum UK servicewomen to occupational fitness.

Methods

Eligible servicewomen will be assigned to a training or control group in a nonrandomized controlled trial 6 weeks after childbirth. Group allocation will be based on the location of standard pregnancy and postpartum care. The control group will receive standard care, with no prescribed intervention. The training group will start an 18-week core and pelvic health rehabilitation program 6 weeks post partum and a 12-week resistance and high-intensity interval training program 12 weeks post partum. All participants will attend 4 testing sessions at 6, 12, 18, and 24 weeks post partum for the assessment of occupational physical performance, pelvic health, psychological well-being, quality of life, and musculoskeletal health outcomes. Occupational physical performance tests will include vertical jump, mid-thigh pull, seated medicine ball throw, and a timed 2-km run. Pelvic health tests will include the Pelvic Organ Prolapse Quantification system, the PERFECT (power, endurance, repetitions, fast, every contraction timed) scheme for pelvic floor strength, musculoskeletal physiotherapy assessment, the Pelvic Floor Distress Inventory–20 questionnaire, and the International Consultation on Incontinence Questionnaire–Vaginal Symptoms. Psychological well-being and quality of life tests will include the World Health Organization Quality of Life questionnaire and the Edinburgh Postnatal Depression Scale. Musculoskeletal health outcomes will include body composition; whole-body areal bone mineral density; tibial volumetric bone mineral density, geometry, and microarchitecture; patella tendon properties; muscle architecture; muscle protein and collagen turnover; and muscle mass and muscle breakdown. Data will be analyzed using linear mixed-effects models, with participants included as random effects, and group and time as fixed effects to assess within- and between-group differences over time.

Results

This study received ethical approval in April 2019 and recruitment started in July 2019. The study was paused in March 2020 owing to the COVID-19 pandemic. Recruitment restarted in May 2021. The results are expected in September 2022.

Conclusions

This study will inform the best practice for the safe and optimal return of postpartum servicewomen to physically and mentally demanding jobs.

Trial Registration

ClinicalTrials.gov NCT04332757; https://clinicaltrials.gov/ct2/show/NCT04332757

International Registered Report Identifier (IRRID)

DERR1-10.2196/32315

One hundred marathons in 100 days: Unique biomechanical signature and the evolution of force characteristics and bone density

BACKGROUND

An extraordinary long-term running performance may benefit from low dynamic loads and a high load-bearing tolerance. An extraordinary runner (age = 55 years, height = 1.81 m, mass = 92 kg) scheduled a marathon a day for 100 consecutive days. His running biomechanics and bone density were investigated to better understand successful long-term running in the master athlete.

METHODS

Overground running gait analysis and bone densitometry were conducted before the marathon-a-day challenge and near its completion. The case's running biomechanics were compared pre-challenge to 31 runners who were matched by a similar foot strike pattern.

RESULTS

The case's peak vertical loading rate (Δx̄ = -61.9 body weight (BW)/s or -57%), peak vertical ground reaction force (Δx̄ = -0.38 BW or -15%), and peak braking force (Δx̄ = -0.118 BW or -31%) were remarkably lower (p < 0.05) than the control group at ∼3.3 m/s. The relatively low loading-related magnitudes were attributed to a remarkably high duty factor (0.41) at the evaluated speed. The foot strike angle of the marathoner (29.5°) was greater than that of the control group, affecting the peak vertical loading rate. Muscle powers in the lower extremity were also remarkably low in the case vs. controls: peak power of knee absorption (Δx̄ = -9.16 watt/kg or -48%) and ankle generation (Δx̄ = -3.17 watt/kg or -30%). The bone mineral density increased to 1.245 g/cm² (+2.98%) near completion of the challenge, whereas the force characteristics showed no statistically significant change.

CONCLUSION

The remarkable pattern of the high-mileage runner may be useful in developing or evaluating load-shifting strategies in distance running.

Sclerostin and Dickkopf-1 Characteristics According to Age and Physical Activity Levels in Premenopausal Women

We aimed to compare serum concentrations of sclerostin and DKK-1 in young (20-30 yrs, n = 25) and middle-aged (35-45 yrs, n = 25) premenopausal women and based on physical activity (PA) status. PA status was assessed by the International Physical Activity Questionnaire (low-moderate (≤ 2999 MET-min/week) and high (≥ 3000 MET-min/week). Serum sclerostin and DKK-1 levels were measured in fasting morning blood samples by ELISA. Areal bone mineral density (aBMD) was measured by DXA, and non-dominant tibia bone characteristics were assessed by pQCT. After adjusting for total body aBMD, middle-aged women had significantly (p < 0.001) higher (0.54 ± 0.01 ng/mL) serum sclerostin than young women (0.41 ± 0.01 ng/mL), and sclerostin was positively correlated with age (r_s = 0.065, p ≤ 0.001) and total PA score (r_s = 0.33, p = 0.021). Young women had higher left trochanter aBMD (p = 0.036) than middle-aged women and aBMD variables were higher (all p ≤ 0.043) in the high active group. Middle-aged women had higher 38% cortical vBMD than young women (p = 0.021), otherwise young women had higher values for pQCT variables (all p ≤ 0.036). Sclerostin showed significant correlations (r = 0.32 to 0.58, all p ≤ 0.026) with spine aBMD for the entire cohort and for each age group. Middle-aged women had significant correlations between sclerostin and hip aBMD sites (r = 0.043 to 0.56, all p ≤ 0.031). Sclerostin and cortical vBMD were positively correlated in the entire cohort (r = 0.35 to 0.50; both p < 0.013); split by age group, middle-aged women had positive correlations (r = 0.45 to 0.61 age and, all p ≤ 0.021) between sclerostin and pQCT variables. No significant differences for physical activity were observed for serum DKK-1 concentrations. Serum sclerostin concentrations were positively associated with age and bone characteristics in premenopausal women; however, these findings were not evident for circulating DKK-1. Further research is needed to elucidate the mechanisms for the discordant results in these Wnt inhibitors.

Longitudinal Tibia Stress Fracture Risk During High-Volume Training: a Multi-Scale Modeling Pipeline Incorporating Bone Remodeling

Tibia stress fractures are prevalent during high-intensity training, yet a mechanistic model linking longitudinal training intensity, bone health, and long-term injury risk has yet to be demonstrated. The objective of this study was to develop and validate a multi-scale model of gross and tissue level loading on the tibia including bone remodeling on a timescale of week. Peak tensile tibial strain (3517 µstrain) during 4 m/s running was below injury thresholds, and the peak anteromedial tibial strain (1248 µstrain) was 0.17 standard deviations away from the mean of reported literature values. An initial study isolated the effects of cortical density and stiffness on tibial strain during a simulated eight week training period. Tibial strains and cortical microcracking correlated to initial cortical modulus, with all simulations presenting peak anteromedial tensile strains (1047-1600 µstrain) near day 11. Average cortical densities decreased by 7-8 percent of their nominal value by day 11, but the overall density change was &lt;2% by the end of the simulated training period, in line with reported results. This study demonstrates the benefits of multi-scale models for investigating stress fracture risk and indicates that peak tibial strain, and thus injury risk, may increase early in a high intensity training program. Future studies could optimize training volume and recovery time to reduce injury risk during the most vulnerable training periods.

Bone Impairment in a Large Cohort of Chinese Patients With Tumor-Induced Osteomalacia Assessed by HR-pQCT and TBS

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by excessive production of fibroblast growth factor 23 (FGF23) by a tumor. Previous studies have revealed generalized mineralization defects and low areal bone mineral density (aBMD) in TIO. However, data on the bone microarchitecture in TIO are limited. In this study, we evaluated the microarchitecture in the peripheral (distal radius and tibia) and axial (lumbar spine) skeleton using high-resolution peripheral quantitative computed tomography (HR-pQCT) and trabecular bone score (TBS) and investigated related factors in a large cohort of Chinese patients with TIO. A total of 186 patients with TIO who had undergone dual-energy X-ray absorptiometry (DXA) or HR-pQCT scans were enrolled. Compared with age-, sex-, and body mass index (BMI)-matched healthy controls, TIO patients (n = 113) had lower volumetric BMD, damaged microstructure, and reduced bone strength in the peripheral skeleton, especially at the tibia. The average TBS obtained from 173 patients was 1.15 ± 0.16. The proportion of patients with abnormal TBS (<1.35) was higher than that with low L₁ to L₄ aBMD Z-score (Z ≤ -2) (43.9% versus 89.6%, p < 0.001). Higher intact fibroblast growth factor 23 (iFGF23), intact parathyroid hormone (iPTH), alkaline phosphatase, and β-isomerized C-terminal telopeptide of type I collagen (β-CTx) levels, more severe mobility impairment, and a history of fracture were associated with poorer HR-pQCT parameters but not with lower TBS. However, greater height loss and longer disease duration were correlated with worse HR-pQCT parameters and TBS. Moreover, TBS was correlated with both trabecular and cortical HR-pQCT parameters in TIO. In conclusion, we revealed impaired bone microarchitecture in the axial and peripheral skeleton in a large cohort of Chinese TIO patients. HR-pQCT parameters and TBS showed promising advantages over aBMD for assessing bone impairment in patients with TIO. A longer follow-up period is needed to observe changes in bone microarchitecture after tumor resection. © 2021 American Society for Bone and Mineral Research (ASBMR).

Once daily calcium (1000 mg) and vitamin D (1000 IU) supplementation during military training prevents increases in biochemical markers of bone resorption but does not affect tibial microarchitecture in Army recruits

Basic combat training (BCT) is a period of novel physical training including load carriage resulting in higher risk of stress fracture compared to any other time during military service. Prior trials reported a 20% reduction in stress fracture incidence with Ca and vitamin D (Ca + D) supplementation (2000 mg Ca, 800 IU vitamin D), and greater increases in tibia vBMD during BCT compared to placebo. The primary objective of this randomized, double-blind, placebo-controlled trial was to determine the efficacy of a lower dose of Ca (1000 mg/d Ca, 1000 IU vit D) on PTH, bone biomarkers and tibial microarchitecture during BCT. One hundred volunteers (50 males, 50 females; mean age 21.8 ± 3.5 y) were block randomized by race and sex to receive a daily Ca + D fortified food bar or placebo. Anthropometrics, dietary intake, fasted blood draws and high resolution pQCT scans of the distal and mid-shaft tibia were obtained at the start of BCT and 8 wks later at the conclusion of training. As compliance was 98% in both treatment groups, an intent-to-treat analysis was used. At the distal tibia, total vBMD, Tb.vBMD, Tb.N, Th.Th and Tb.BV/TV increased (+1.07 to 2.12% for all, p < 0.05) and Tb.Sp decreased (0.96 to 1.09%, p < 0.05) in both treatment groups. At the mid-shaft, Ct.Pm increased (+0.18 to 0.21%, p = 0.01) and Ct.vBMD decreased (-0.48 to -0.77%, p < 0.001) in both groups. Ca + D prevented increases in CTX and TRAP, which were observed in the placebo group (group-by-time, p < 0.05). Mean circulating 25OHD, BAP, P1NP and iCa increased and PTH decreased in both treatment groups (p < 0.05). These results, in agreement with other studies, suggest that bone microarchitectural changes indicative of bone formation occur during BCT. While Ca + D supplementation at lower doses than those tested in previous studies prevented increases in biochemical markers of bone resorption in this study, there were no significant changes in bone tissue after 8 wks of Army BCT.

Muscle-derived factors influencing bone metabolism

A significant amount of attention has been brought to the endocrine-like function of skeletal muscle on various tissues, particularly with bone. Several lines of investigation indicate that the physiology of both bone and muscle systems may be regulated by a given stimulus, such as exercise, aging, and inactivity. Moreover, emerging evidence indicates that bone is heavily influenced by soluble factors derived from skeletal muscle (i.e., muscle-to-bone communication). The purpose of this review is to discuss the regulation of bone remodeling (formation and/or resorption) through skeletal muscle-derived cytokines (hereafter myokines) including the anti-inflammatory cytokine METRNL and pro-inflammatory cytokines (e.g., TNF-α, IL-6, FGF-2 and others). Our goal is to highlight possible therapeutic opportunities to improve muscle and bone health in aging.

Breakfast Skipping Is Associated with Vitamin D Deficiency among Young Adults entering Initial Military Training

BACKGROUND

Vitamin D deficiency (VDD), defined as serum 25-hydroxyvitamin D (25[OH]D) levels < 20 ng/mL [to convert 25[OH]D ng/mL to nmol/L, multiply by 2.5]) is prevalent in young adults and has been associated with adverse health outcomes, including stress fracture during periods of increased physical activity such as military training. Foods commonly consumed at breakfast provide an important source of vitamin D, yet breakfast skipping is common among young adults. However, whether breakfast skipping is associated with VDD in young adults is unclear.

OBJECTIVES

This study aimed to determine whether breakfast skipping is associated with odds of VDD among recruits entering initial military training (IMT), and with changes in serum 25(OH)D during IMT. In addition, whether diet quality and vitamin D intake mediated these associations was determined.

DESIGN

Secondary analysis of individual participant data collected during five IMT studies. Breakfast skipping (≥ 3 times/week) was self-reported. Dietary intake was determined using food frequency questionnaires, and vitamin D status was assessed using circulating 25(OH)D concentrations pre- and post-IMT.

PARTICIPANTS AND SETTING

Participants were healthy US Army, US Air Force, and US Marine recruits (N = 1,569, 55% male, mean ± standard deviation age 21 ± 4 years) entering military service between 2010 and 2015 at Fort Jackson, SC; Fort Sill, OK; Lakeland Air Force Base, TX; or the Marine Corps Recruit Depot, Parris Island, SC.

MAIN OUTCOME MEASURES

Primary outcomes were VDD pre-IMT and change in 25(OH)D from pre- to post-IMT.

STATISTICAL ANALYSIS PERFORMED

Associations were determined using multivariate-adjusted logistic and linear regression and mediation models.

RESULTS

Forty-six percent of military recruits were classified as breakfast skippers pre-IMT, and 30% were VDD. Breakfast skipping was associated with a higher odds of pre-IMT VDD (odds ratio 1.5, 95% CI 1.1 to 1.9), and lower vitamin D intake and diet quality were partial mediators of the association. Serum 25(OH)D concentrations improved (P = 0.01) among habitual breakfast skippers versus nonskippers during IMT; however, regression to the mean could not be ruled out. Neither change in diet quality nor vitamin D intake were associated with change in 25(OH)D concentrations during IMT.

CONCLUSIONS

Breakfast skipping is prevalent among incoming military recruits and is associated with VDD. This relationship may be mediated by lower diet quality and vitamin D intake.

Bone, Biomarker, Body Composition, and Performance Responses to 8 Weeks of ROTC Training

CONTEXT

Military personnel engage in vigorous exercise, often resulting in higher bone mineral density; however, lower leg bone injuries are common in this population. Predictors of change in tibial bone quality and strength need to be characterized in this high-risk population.

OBJECTIVE

This study aimed to examine the effects of an eight-week military training intervention on total body and site-specific bone density and tibial bone quality, serum biomarkers (parathyroid hormone and sclerostin), body composition, and physical performance. Additionally, we sought to investigate what outcome variables (biomarkers, body composition, physical performance) would be predictive of estimated tibial bone strength in college-aged Reserve Officers' Training Corps (ROTC) members.

DESIGN

Prospective Cohort Study.

SETTING

XXX University. Patients of Other Participants: ROTC (n=14 male; n=4 female) were matched for sex, age, and body mass to physically active Controls (n=14 male; n=4 female). ROTC engaged in an eight-week training intervention, while physically active Controls made no changes to their exercise routines.

MAIN OUTCOME MEASURES

Pre general health questionnaires and pre, mid, and post intervention bone scans (DXA, pQCT), serum blood draws (parathyroid hormone and sclerostin), and physical performance measures (muscle strength and aerobic capacity) were tested.

RESULTS

ROTC participants exhibited significantly increased hip bone density and content (all p≤0.03) after the eight-week intervention. Sclerostin, not PTH, was a significant positive correlate and predictor in all ROTC models for estimated bone strength at the fracture prone 38% tibial site. Both groups decreased total body and regional fat mass and ROTC increased aerobic capacity (all p≤0.05).

CONCLUSIONS

All bone, body composition, and performance measures either improved or were maintained in response to ROTC training and sclerostin should be further investigated as a potential early indicator of changes in estimated tibial bone strength in military cohorts.

Promoting adaptive bone formation to prevent stress fractures in military personnel

Mechanical loading leads to adaptive bone formation - the formation of new bone on existing skeletal surfaces - which increases bone strength and fatigue resistance. The same mechanical loading can also cause microdamage to bone and development of a stress fracture through targeted remodelling. Stress fractures are common in military recruits and cause significant morbidity, lost training time, and discharge from military service. This narrative review proposes strategies to promote adaptive bone formation as a novel approach to mitigate the risk of stress fracture injuries during arduous military training. Exercise that is unaccustomed, dynamic, high-impact, multidirectional, intermittent, and includes extended rest periods to restore bone mechanosensitivity, is most osteogenic. New bone formation can take up to one year to mineralize, and so new exercise training programmes should be initiated well in advance of military activities with high risk of stress fracture. Bone mechanosensitivity is highest in adolescence, before puberty, and so increasing physical activity in youth is likely to protect skeletal health in later life, including for those in the military. Recent data show that adaptive bone formation takes place during initial military training. Adaptive bone formation can also be supported with adequate sleep, vitamin D, calcium, and energy availability. Further evidence on how strategies to promote adaptive bone formation affect stress fracture risk are required. Adaptive bone formation can be optimized with a range of training and nutritional strategies to help create a resilient skeleton, which may protect against stress fracture throughout military service.

Tibial Macrostructure and Microarchitecture Adaptations in Women During 44 Weeks of Arduous Military Training

Bone adapts to unaccustomed, high-impact loading but loses mechanosensitivity quickly. Short periods of military training (≤12 weeks) increase the density and size of the tibia in women. The effect of longer periods of military training, where the incidence of stress fracture is high, on tibial macrostructure and microarchitecture in women is unknown. This observational study recruited 51 women (age 19 to 30 years) at the start of 44 weeks of British Army Officer training. Tibial volumetric bone mineral density (vBMD), geometry, and microarchitecture were measured by high-resolution peripheral quantitative computed tomography (HRpQCT). Scans of the right tibial metaphysis (4% site) and diaphysis (30% site) were performed at weeks 1, 14, 28, and 44. Measures of whole-body areal bone mineral density (aBMD) were obtained using dual-energy X-ray absorptiometry (DXA). Blood samples were taken at weeks 1, 28, and 44, and were analyzed for markers of bone formation and resorption. Trabecular vBMD increased from week 1 to 44 at the 4% site (3.0%, p < .001). Cortical vBMD decreased from week 1 to 14 at the 30% site (-0.3%, p < .001). Trabecular area decreased at the 4% site (-0.4%); trabecular bone volume fraction (3.5%), cortical area (4.8%), and cortical thickness (4.0%) increased at the 4% site; and, cortical perimeter increased at the 30% site (0.5%) from week 1 to 44 (p ≤ .005). Trabecular number (3.5%) and thickness (2.1%) increased, and trabecular separation decreased (-3.1%), at the 4% site from week 1 to 44 (p < .001). Training increased failure load at the 30% site from week 1 to 44 (2.5%, p < .001). Training had no effect on aBMD or markers of bone formation or resorption. Tibial macrostructure and microarchitecture continued to adapt across 44 weeks of military training in young women. Temporal decreases in cortical density support a role of intracortical remodeling in the pathogenesis of stress fracture. © 2021 Crown copyright. Journal of Bone and Mineral Research © 2021 American Society for Bone and Mineral Research (ASBMR). This article is published with the permission of the Controller of HMSO and the Queen's Printer for Scotland.

Bone Mechanoregulation Allows Subject-Specific Load Estimation Based on Time-Lapsed Micro-CT and HR-pQCT in Vivo

Patients at high risk of fracture due to metabolic diseases frequently undergo long-term antiresorptive therapy. However, in some patients, treatment is unsuccessful in preventing fractures or causes severe adverse health outcomes. Understanding load-driven bone remodelling, i.e., mechanoregulation, is critical to understand which patients are at risk for progressive bone degeneration and may enable better patient selection or adaptive therapeutic intervention strategies. Bone microarchitecture assessment using high-resolution peripheral quantitative computed tomography (HR-pQCT) combined with computed mechanical loads has successfully been used to investigate bone mechanoregulation at the trabecular level. To obtain the required mechanical loads that induce local variances in mechanical strain and cause bone remodelling, estimation of physiological loading is essential. Current models homogenise strain patterns throughout the bone to estimate load distribution in vivo, assuming that the bone structure is in biomechanical homoeostasis. Yet, this assumption may be flawed for investigating alterations in bone mechanoregulation. By further utilising available spatiotemporal information of time-lapsed bone imaging studies, we developed a mechanoregulation-based load estimation (MR) algorithm. MR calculates organ-scale loads by scaling and superimposing a set of predefined independent unit loads to optimise measured bone formation in high-, quiescence in medium-, and resorption in low-strain regions. We benchmarked our algorithm against a previously published load history (LH) algorithm using synthetic data, micro-CT images of murine vertebrae under defined experimental in vivo loadings, and HR-pQCT images from seven patients. Our algorithm consistently outperformed LH in all three datasets. In silico-generated time evolutions of distal radius geometries (n = 5) indicated significantly higher sensitivity, specificity, and accuracy for MR than LH (p < 0.01). This increased performance led to substantially better discrimination between physiological and extra-physiological loading in mice (n = 8). Moreover, a significantly (p < 0.01) higher association between remodelling events and computed local mechanical signals was found using MR [correct classification rate (CCR) = 0.42] than LH (CCR = 0.38) to estimate human distal radius loading. Future applications of MR may enable clinicians to link subtle changes in bone strength to changes in day-to-day loading, identifying weak spots in the bone microstructure for local intervention and personalised treatment approaches.

Bone Microarchitecture and Strength Adaptation to Physical Activity: A Within-Subject Controlled HRpQCT Study

PURPOSE

Physical activity benefits bone mass and cortical bone size. The current study assessed the impact of chronic (≥10 yr) physical activity on trabecular microarchitectural properties and microfinite element analyses of estimated bone strength.

METHODS

Female collegiate-level tennis players (n = 15; age = 20.3 ± 0.9 yr) were used as a within-subject controlled model of chronic unilateral upper-extremity physical activity. Racquet-to-nonracquet arm differences at the distal radius and radial diaphysis were assessed using high-resolution peripheral quantitative computed tomography. The distal tibia and the tibial diaphysis in both legs were also assessed, and cross-country runners (n = 15; age = 20.8 ± 1.2 yr) included as controls.

RESULTS

The distal radius of the racquet arm had 11.8% (95% confidence interval [CI] = 7.9% to 15.7%) greater trabecular bone volume/tissue volume, with trabeculae that were greater in number, thickness, connectivity, and proximity to each other than that in the nonracquet arm (all P < 0.01). Combined with enhanced cortical bone properties, the microarchitectural advantages at the distal radius contributed a 18.7% (95% CI = 13.0% to 24.4%) racquet-to-nonracquet arm difference in predicted load before failure. At the radial diaphysis, predicted load to failure was 9.6% (95% CI = 6.7% to 12.6%) greater in the racquet versus nonracquet arm. There were fewer and smaller side-to-side differences at the distal tibia; however, the tibial diaphysis in the leg opposite the racquet arm was larger with a thicker cortex and had 4.4% (95% CI = 1.7% to 7.1%) greater strength than the contralateral leg.

CONCLUSION

Chronically elevated physical activity enhances trabecular microarchitecture and microfinite element estimated strength, furthering observations from short-term longitudinal studies. The data also demonstrate that tennis players exhibit crossed symmetry wherein the leg opposite the racquet arm possesses enhanced tibial properties compared with in the contralateral leg.

Biomechanical Basis of Predicting and Preventing Lower Limb Stress Fractures During Arduous Training

PURPOSE OF REVIEW

Stress fractures at weight-bearing sites, particularly the tibia, are common in military recruits and athletes. This review presents recent findings from human imaging and biomechanics studies aimed at predicting and preventing stress fractures.

RECENT FINDINGS

Peripheral quantitative computed tomography (pQCT) provides evidence that cortical bone geometry (tibial width and area) is associated with tibial stress fracture risk during weight-bearing exercise. The contribution of bone trabecular microarchitecture, cortical porosity, and bone material properties in the pathophysiology of stress fractures is less clear, but high-resolution pQCT and new techniques such as impact microindentation may improve our understanding of the role of microarchitecture and material properties in stress fracture prediction. Military studies demonstrate osteogenic outcomes from high impact, repetitive tibial loading during training. Kinetic and kinematic characteristics may influence stress fracture risk, but there is no evidence that interventions to modify biomechanics can reduce the incidence of stress fracture. Strategies to promote adaptive bone formation, in combination with improved techniques to assess bone strength, present exciting opportunities for future research to prevent stress fractures.

Differences in the effects of BMI on bone microstructure between loaded and unloaded bones assessed by HR-pQCT in Japanese postmenopausal women

Objectives

The relationship between weight-related load and bone mineral density (BMD)/bone microstructure under normal load conditions using high-resolution peripheral quantitative computed tomography (HR-pQCT) remains unconfirmed. The study aims to investigate the differences in effect of body mass index (BMI) on BMD/bone microstructure of loaded and unloaded bones, respectively, in Japanese postmenopausal women.

Methods

Fifty-seven postmenopausal women underwent HR-pQCT on the tibia and radius. Correlation analysis, principal component (PC) analysis, and hierarchical multiple regression were performed to examine the relationship between BMI and HR-pQCT parameters.

Results

Several microstructural parameters of the tibia and radius correlated with BMI through a simple correlation analysis, and these relationships remained unchanged even with an age-adjusted partial correlation analysis. PC analysis was conducted using seven bone microstructure parameters. The first PC (PC1) reflected all parameters of trabecular and cortical bone microstructures, except for cortical porosity, whereas the second PC (PC2) reflected only cortical bone microstructure. Hierarchical multiple regression analysis indicated that BMI was more strongly related to BMD/bone microstructure in the tibia than in the radius. Furthermore, BMI was associated with trabecular/cortical BMD, and PC1 (not PC2) of the tibia and radius. Thus, BMI was strongly related to the trabecular bone microstructure rather than the cortical bone microstructure.

Conclusions

Our data confirmed that BMI is associated with volumetric BMD and trabecular bone microstructure parameters in the tibia and radius. However, although BMI may be more related to HR-pQCT parameters in the tibia than in the radius, the magnitude of association is modest.

High-impact exercise stimulated localised adaptation of microarchitecture across distal tibia in postmenopausal women

We provided evidence that a 6-month regular hopping exercise intervention can increase trabecular number and possibly trabecular volume fraction of the distal tibia. Our novel localised analysis demonstrated region-specific changes, predominantly in the anterior region, in postmenopausal women.

INTRODUCTION

The localisation of bone remodelling and microarchitectural adaptation to exercise loading has not been demonstrated previously in vivo in humans. The aim of this study is to assess the feasibility of using 3D image registration and high-resolution peripheral quantitative computed tomography (HR-pQCT) to investigate the effect of high-impact exercise on human trabecular bone variables and remodelling rate across the distal tibia.

METHODS

Ten postmenopausal women were recruited for 6-month unilateral hopping exercises, with HR-pQCT scans taken of both exercise leg (EL) and control leg (CL) for each participant before and after the intervention. A 3D image registration was used to ensure measurements were taken at the same region. Short-term reproducibility tests were conducted prior to the assessment using identical setup. The results were assessed comparing CL and EL, and interaction (time × leg) using a two-way repeated measures analysis of variance (RM-ANOVA).

RESULTS

Across the whole tibia, we observed significant increases in trabecular number (Tb.N) (+ 4.4%) and trabecular bone formation rate (tBFR) (3.3%), and a non-significant increase in trabecular bone volume fraction (BV/TV) (+ 1%) in the EL. Regional resorption was higher in the CL than the EL, with this difference being statistically significant at the lateral tibia. In the EL, tBFR was significantly higher in the anterior region than the medial but a trabecular bone resorption rate (tBRR) showed no significant regional variation. Conversely in the CL, both tBFR and tBRR were significantly higher in the anterior and lateral than the medial region.

CONCLUSION

We demonstrated that it was possible to detect exercise-related bone adaptation with 3D registration of HR-pQCT scan data. Regular hopping exercise increased Tb.N and possibly BV/TV across the whole distal tibia. A novel finding of the study was that tBFR and tBRR responses to loading were localised: changes were achieved by formation rate exceeding resorption rate in the exercise leg, both globally and at the anterior region where turnover was greatest.

TRIAL REGISTRATION

clinicaltrials.gov : NCT03225703.

Musculoskeletal injuries in military personnel-Descriptive epidemiology, risk factor identification, and prevention

OBJECTIVES

To provide an overall perspective on musculoskeletal injury (MSI) epidemiology, risk factors, and preventive strategies in military personnel.

DESIGN

Narrative review.

METHODS

The thematic session on MSIs in military personnel at the 5th International Congress on Soldiers' Physical Performance (ICSPP) included eight presentations on the descriptive epidemiology, risk factor identification, and prevention of MSIs in military personnel. Additional topics presented were bone anabolism, machine learning analysis, and the effects of non-steroidal anti-inflammatory drugs (NSAIDs) on MSIs. This narrative review focuses on the thematic session topics and includes identification of gaps in existing literature, as well as areas for future study.

RESULTS

MSIs cause significant morbidity among military personnel. Physical training and occupational tasks are leading causes of MSI limited duty days (LDDs) for the U.S. Army. Recent studies have shown that MSIs are associated with the use of NSAIDs. Bone MSIs are very common in training; new imaging technology such as high resolution peripheral quantitative computed tomography allows visualization of bone microarchitecture and has been used to assess new bone formation during military training. Physical activity monitoring and machine learning have important applications in monitoring and informing evidence-based solutions to prevent MSIs.

CONCLUSIONS

Despite many years of research, MSIs continue to have a high incidence among military personnel. Areas for future research include quantifying exposure when determining MSI risk; understanding associations between health-related components of physical fitness and MSI occurrence; and application of innovative imaging, physical activity monitoring and data analysis techniques for MSI prevention and return to duty.

Emerging evidence that adaptive bone formation inhibition by non-steroidal anti-inflammatory drugs increases stress fracture risk

There is mounting evidence suggesting that the commonly used analgesics, non-steroidal anti-inflammatory drugs (NSAIDs), may inhibit new bone formation with physical training and increase risk of stress fractures in physically active populations. Stress fractures are thought to occur when bones are subjected to repetitive mechanical loading, which can lead to a cycle of tissue microdamage, repair, and continued mechanical loading until fracture. Adaptive bone formation, particularly on the periosteal surface of long bones, is a concurrent adaptive response of bone to heightened mechanical loading that can improve the fatigue resistance of the skeletal structure, and therefore may play a critical role in offsetting the risk of stress fracture. Reports from animal studies suggest that NSAID administration may suppress this important adaptive response to mechanical loading. These observations have implications for populations such as endurance athletes and military recruits who are at risk of stress fracture and whose use of NSAIDs is widespread. However, results from human trials evaluating exercise and bone adaptation with NSAID consumption have been less conclusive. In this review, we identify knowledge gaps that must be addressed to further support NSAID-related guidelines intended for at-risk populations and individuals.

Supplementary Energy Increases Bone Formation during Arduous Military Training

PURPOSE

This study aimed to investigate the effect of supplementary energy on bone formation and resorption during arduous military training in energy deficit.

METHODS

Thirty male soldiers completed an 8-wk military combat course (mean ± SD, age = 25 ± 3 yr, height = 1.78 ± 0.05 m, body mass = 80.9 ± 7.7 kg). Participants received either the habitual diet (control group, n = 15) or an additional 5.1 MJ·d-1 to eliminate the energy deficit (supplemented group, n = 15). Circulating markers of bone formation and resorption, and reproductive, thyroid, and metabolic status, were measured at baseline and weeks 6 and 8 of training.

RESULTS

Bone-specific alkaline phosphatase decreased in controls (-4.4 ± 1.9 μg·L-1) and increased in the supplemented group (16.0 ± 6.6 μg·L-1), between baseline and week 8 (P < 0.001). Procollagen type 1 N-terminal propeptide increased between baseline and week 6 for both groups (5.6 ± 8.1 μg·L-1, P = 0.005). Beta carboxy-terminal cross-linking telopeptide of type 1 collagen decreased between baseline and week 8 for both groups (-0.16 ± 0.20 μg·L-1, P < 0.001). Prolactin increased from baseline to week 8 for the supplemented group (148 ± 151 IU·L-1, P = 0.041). The increase in adiponectin from baseline to week 8 was higher in controls (4.3 ± 1.8 mg·L-1, P < 0.001) than that in the supplemented group (1.4 ± 1.0 mg·L-1, P < 0.001). Insulin-like growth factor binding protein-3 was lower at week 8 than baseline for controls (-461 ± 395 ng·mL-1, P < 0.001).

CONCLUSION

The increase in bone-specific alkaline phosphatase, a marker of bone formation, with supplementation supports a role of energy in osteoblastic activity; the implications for skeletal adaptation and stress fracture risk are unclear. The mechanism is likely through protecting markers of metabolic, but not reproductive or thyroid, function.

Changes in Volumetric Bone Mineral Density Over 12 Months After a Tibial Bone Stress Injury Diagnosis: Implications for Return to Sports and Military Duty

BACKGROUND

Bone stress injuries (BSIs) occur in up to 20% of runners and military personnel. Typically, after a period of unloading and gradual return to weightbearing activities, athletes return to unrestricted sports participation or military duty approximately 4 to 14 weeks after a BSI diagnosis, depending on the injury location and severity. However, the time course of the recovery of the bone's mechanical competence is not well-characterized, and reinjury rates are high.

PURPOSE

To assess the bone microarchitecture and volumetric bone mineral density (vBMD) over 12 months after a tibial BSI diagnosis.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

We enrolled 30 female athletes from the local community (aged 18-35 years) with a tibial BSI (grade ≥2 of 4 on magnetic resonance imaging) for this prospective observational study. Participants completed a baseline visit within 3 weeks of the diagnosis. At baseline and 6, 12, 24, and 52 weeks after the BSI diagnosis, we collected high-resolution peripheral quantitative computed tomography scans of the ultradistal tibia (4% of tibial length) of the injured and uninjured legs as well as pain and physical activity assessment findings.

RESULTS

From baseline to 12 weeks after the diagnosis, total, trabecular, and cortical vBMD declined by 0.58% to 0.94% (P < .05 for all) in the injured leg. Total and trabecular vBMD also declined by 0.61% and 0.67%, respectively, in the uninjured leg (P < .05 for both). At 24 weeks, mean values for all bone parameters were nearly equivalent to baseline values, and by 52 weeks, several mean values had surpassed baseline values. Of the 30 participants, 10 incurred a subsequent BSI during the course of the study, and 1 of these 10 incurred 2 subsequent BSIs. Participants who suffered an additional BSI were younger and had a later age of menarche, a greater incidence of previous fractures, and lower serum parathyroid hormone levels (P < .05 for all).

CONCLUSION

Bone density declined in both the injured and the uninjured legs and, on average, did not return to baseline for 3 to 6 months after a tibial BSI diagnosis. The observed time to the recovery of baseline vBMD, coupled with the high rate of recurrent BSIs, suggests that improved return-to-sports and military duty guidelines may be in order.

The Central Role of Osteocytes in the Four Adaptive Pathways of Bone's Mechanostat

We review evidence supporting an updated mechanostat model in bone that highlights the central role of osteocytes within bone's four mechanoadaptive pathways: 1) formation modeling and 2) targeted remodeling, which occur with heightened mechanical loading, 3) resorption modeling, and 4) disuse-mediated remodeling, which occur with disuse. These four pathways regulate whole-bone stiffness in response to changing mechanical demands.

Guidelines for the assessment of bone density and microarchitecture in vivo using high-resolution peripheral quantitative computed tomography

INTRODUCTION

The application of high-resolution peripheral quantitative computed tomography (HR-pQCT) to assess bone microarchitecture has grown rapidly since its introduction in 2005. As the use of HR-pQCT for clinical research continues to grow, there is an urgent need to form a consensus on imaging and analysis methodologies so that studies can be appropriately compared. In addition, with the recent introduction of the second-generation HrpQCT, which differs from the first-generation HR-pQCT in scan region, resolution, and morphological measurement techniques, there is a need for guidelines on appropriate reporting of results and considerations as the field adopts newer systems.

METHODS

A joint working group between the International Osteoporosis Foundation, American Society of Bone and Mineral Research, and European Calcified Tissue Society convened in person and by teleconference over several years to produce the guidelines and recommendations presented in this document.

RESULTS

An overview and discussion is provided for (1) standardized protocol for imaging distal radius and tibia sites using HR-pQCT, with the importance of quality control and operator training discussed; (2) standardized terminology and recommendations on reporting results; (3) factors influencing accuracy and precision error, with considerations for longitudinal and multi-center study designs; and finally (4) comparison between scanner generations and other high-resolution CT systems.

CONCLUSION

This article addresses the need for standardization of HR-pQCT imaging techniques and terminology, provides guidance on interpretation and reporting of results, and discusses unresolved issues in the field.

Energy Deficiency in Soldiers: The Risk of the Athlete Triad and Relative Energy Deficiency in Sport Syndromes in the Military

Military personnel experience energy deficit (total energy expenditure higher than energy intake), particularly during combat training and field exercises where exercising energy expenditures are high and energy intake is reduced. Low energy availability (energy intake minus exercising energy expenditure expressed relative to fat free mass) impairs endocrine function and bone health, as recognized in female athletes as the Female Athlete Triad syndrome. More recently, the Relative Energy Deficiency in Sport (RED-S) syndrome encompasses broader health outcomes, physical and cognitive performance, non-athletes, and men. This review summarizes the evidence for the effect of low energy availability and energy deficiency in military training and operations on health and performance outcomes. Energy availability is difficult to measure in free-living individuals but doubly labeled water studies demonstrate high total energy expenditures during military training; studies that have concurrently measured energy intake, or measured body composition changes with DXA, suggest severe and/or prolonged energy deficits. Military training in energy deficit disturbs endocrine and metabolic function, menstrual function, bone health, immune function, gastrointestinal health, iron status, mood, and physical and cognitive performance. There are more data for men than women, and little evidence on the chronic effects of repeated exposures to energy deficit. Military training impairs indices of health and performance, indicative of the Triad and RED-S, but the multi-stressor environment makes it difficult to isolate the independent effects of energy deficiency. Studies supplementing with energy to attenuate the energy deficit suggest an independent effect of energy deficiency in the disturbances to metabolic, endocrine and immune function, and physical performance, but randomized controlled trials are lacking.

Evolutionary Perspectives on the Developing Skeleton and Implications for Lifelong Health

Osteoporosis is a significant cause of morbidity and mortality in contemporary populations. This common disease of aging results from a state of bone fragility that occurs with low bone mass and loss of bone quality. Osteoporosis is thought to have origins in childhood. During growth and development, there are rapid gains in bone dimensions, mass, and strength. Peak bone mass is attained in young adulthood, well after the cessation of linear growth, and is a major determinant of osteoporosis later in life. Here we discuss the evolutionary implications of osteoporosis as a disease with developmental origins that is shaped by the interaction among genes, behavior, health status, and the environment during the attainment of peak bone mass. Studies of contemporary populations show that growth, body composition, sexual maturation, physical activity, nutritional status, and dietary intake are determinants of childhood bone accretion, and provide context for interpreting bone strength and osteoporosis in skeletal populations. Studies of skeletal populations demonstrate the role of subsistence strategies, social context, and occupation in the development of skeletal strength. Comparisons of contemporary living populations and archeological skeletal populations suggest declines in bone density and strength that have been occurring since the Pleistocene. Aspects of western lifestyles carry implications for optimal peak bone mass attainment and lifelong skeletal health, from increased longevity to circumstances during development such as obesity and sedentism. In light of these considerations, osteoporosis is a disease of contemporary human evolution and evolutionary perspectives provide a key lens for interpreting the changing global patterns of osteoporosis in human health.

Skeletal loading score is associated with bone microarchitecture in young adults

Physical activity that involves high strain magnitudes and high rates of loading is reported to be most effective in eliciting an osteogenic bone response. Whether a history of participation in osteogenic activities during youth, as well as current participation in osteogenic activities, contributes to young adult bone microarchitecture and strength is unknown.

PURPOSE

We determined the association between a new skeletal loading (SkL) score reflecting physical activity from age 11 to adulthood, the bone specific physical activity questionnaire (BPAQ) and bone microarchitecture in young Black and White men and women.

METHODS

We conducted a cross-sectional study of young ([mean ± SD] 23.7 ± 3.3 years) Black (n = 51 women, n = 31 men) and White (n = 50 women, n = 49 men) adults. Microarchitecture and estimated bone strength (by micro-finite element analysis) were assessed at the ultradistal tibia using high-resolution peripheral quantitative computed tomography (HR-pQCT). Physical activity questionnaires were administered and a SkL score was derived based on ground reaction force, rate of loading, frequency, duration, and life period of participation per activity from age 11 onwards. BPAQ score was also calculated. We used multiple linear regression to determine associations between both SkL score and BPAQ score and bone outcomes, adjusting for age, height, weight, sex, and race.

RESULTS

We found that SkL score, which accounts for current and historical physical activity, was significantly associated with most cortical bone parameters at the tibia including area, area fraction, porosity, thickness, and tissue mineral density (R² = 0.27-0.55, all p < 0.01). Further, trabecular thickness, separation, number, and bone mineral density (R² = 0.22-0.32, all p < 0.01), as well as stiffness and failure load (R² = 0.63-0.65, all p < 0.01), were associated with the SkL score. The BPAQ was also significantly associated with most bone parameters, but to a lesser degree than SkL score.

CONCLUSION

These findings suggest that among young adults, greater amounts of osteogenic physical activity, as assessed by the SkL score and BPAQ are associated with improved bone microarchitecture and strength. With the potential to predict bone parameters in young adults, these scores may ultimately serve to identify those most vulnerable to fracture.

Skeletal macro- and microstructure adaptations in men undergoing arduous military training

PURPOSE

Short periods of basic military training increase the density and size of the tibia, but the adaptive response of bone microarchitecture, a key component of bone strength, is not fully understood.

METHODS

Tibial volumetric bone mineral density (vBMD), geometry, microarchitecture and mechanical properties were measured using high-resolution peripheral quantitative computed tomography in 43 male British Army infantry recruits (mean ± SD, age 21 ± 3 years, height 1.76 ± 0.06 m, body mass 76.5 ± 9.4 kg). Bilateral scans were performed at the distal tibia at the start (week 1) and end (week 13) of basic military training. Concurrent measures were obtained for whole-body areal bone mineral density (aBMD) using DXA, and markers of bone metabolism (βCTX, P1NP, PTH, total 25(OH)D and ACa) from venous blood.

RESULTS

Training increased areal BMD for total body (1.4%) and arms (5.2%) (P ≤ 0.031), but not legs and trunk (P ≥ 0.094). Training increased trabecular (1.3 to 1.9%) and cortical vBMD (0.6 to 0.9%), trabecular volume (1.3 to 1.9%), cortical thickness (3.2 to 5.2%) and cortical area (2.6 to 2.8%), and reduced trabecular area (-0.4 to -0.5%) in both legs (P < 0.001). No changes in trabecular number, thickness and separation, cortical porosity, stiffness or failure load were observed (P ≥ 0.188). βCTX decreased (-0.11 μg∙l^-1, P < 0.001) and total 25(OH)D increased (9.4 nmol∙l^-1, P = 0.029), but no differences in P1NP, PTH or ACa were observed between timepoints (P ≥ 0.233).

CONCLUSION

A short period of basic military training increased density and altered geometry of the distal tibia in male military recruits. The osteogenic effects of basic military training are likely due to an increase in unaccustomed, dynamic and high-impact loading.

Regional Changes in Density and Microarchitecture in the Ultradistal Tibia of Female Recruits After U.S. Army Basic Combat Training

Musculoskeletal injuries, such as stress fracture, are responsible for over 10-million lost-duty days among U.S. Army Soldiers. During Basic Combat Training (BCT), an 8- to 10-week program that transforms civilians into Soldiers, women are four times more likely than men to sustain a stress fracture. In this work, we performed high-resolution peripheral quantitative computed tomography scans on the ultradistal tibia of 90 female recruits [age = 21.5 ± 3.3 (mean ± standard deviation) years] before the start of BCT and after 8 weeks into BCT. Then, we divided the scanned bone volume into four sectors-lateral, posterior, medial, and anterior-and computed the bone density and microarchitectural parameters in each of the four sectors pre- and post-BCT. We used linear mixed models to estimate the mean difference for bone density and microarchitectural parameters, while controlling for age, race, and pre-BCT body mass index. Our results revealed that the total volumetric bone mineral density, trabecular volumetric bone mineral density, and trabecular thickness increased (p < 0.05) in each of the four sectors. In addition, cortical thickness and trabecular bone volume/total volume increased in both medial and posterior sectors (p < 0.05). Overall, six and five out of nine parameters improved in the medial and posterior sectors, respectively, after BCT. In conclusion, the heightened physical activity during BCT led to the most beneficial bone adaptation in the medial and posterior sectors of the ultradistal tibia, which is indicative of higher loading in these sectors during activities performed in the course of BCT.

A prospective field study of U.S. Army trainees to identify the physiological bases and key factors influencing musculoskeletal injuries: a study protocol

BACKGROUND

Musculoskeletal injuries (MSKIs) are common in military trainees and present a considerable threat to occupational fitness, deployability, and overall military readiness. Despite the negative effects of MSKIs on military readiness, comprehensive evaluations of the key known and possible risk factors for MSKIs are lacking. The U.S. Army Research Institute of Environmental Medicine (ARIEM) is initiating a large-scale research effort, the ARIEM Reduction in Musculoskeletal Injury (ARMI) Study, to better understand the interrelationships among a wide range of potential MSKI risk factors in U.S. Army trainees in order to identify those risk factors that most contribute to MSKI and may be best targeted for effective mitigation strategies.

METHODS

This prospective study aims to enroll approximately 4000 (2000 male and 2000 female) U.S. Army trainees undergoing Basic Combat Training (BCT). Comprehensive in-person assessments will be completed at both the beginning and end of BCT. Participants will be asked to complete surveys of personal background information, medical history, physical activity, sleep behaviors, and personality traits. Physical measurements will be performed to assess anthropometrics, tibial microarchitecture and whole body bone mineral density, muscle cross-sectional area, body composition, and muscle function. Blood sampling will be also be conducted to assess musculoskeletal, genetic, and nutritional biomarkers of risk. In addition, participants will complete weekly surveys during BCT that examine MSKI events, lost training time, and discrete risk factors for injury. Participants' medical records will be tracked for the 2 years following graduation from training to identify MSKI events and related information. Research hypotheses focus on the development of a multivariate prediction model for MSKI.

DISCUSSION

Results from this study are expected to inform current understanding of known and potential risk factors for MSKIs that can be incorporated into solutions that optimize Soldier health and enhance military readiness.

Calcium and vitamin D supplementation and bone health in Marine recruits: Effect of season

Stress fractures are common overuse injuries caused by repetitive bone loading. These fractures are of particular concern for military recruits and athletes resulting in attrition in up to 60% of recruits that sustain a fracture. Army and Navy recruits supplemented with daily calcium and vitamin D (Ca + D) demonstrated improved bone strength and reduced stress fractures. The aim of the current study was to evaluate whether Ca + D supplementation improves measures of bone health in recruits undergoing United States Marine Corps initial military training (IMT), and whether the effect of supplementation on indices of bone health varied by season. One-hundred ninety-seven Marine recruits (n = 107 males, n = 90 females, mean age = 18.9 ± 1.6 y) were randomized to receive either Ca + D fortified snack bars (2000 mg Ca and 1000 IU vitamin D per day) or placebo divided into twice daily doses during 12 weeks of IMT. Anthropometrics, fasted blood samples, and peripheral quantitative computed tomography (pQCT) scans of the tibial metaphysis and diaphysis were collected upon entrance to- and post-training (12 weeks later). Half of the volunteers entered training in July and the other half started in February. Time-by-group interactions were observed for vitamin D status (25OHD) and the bone turnover markers, BAP, TRAP and OCN. 25OHD increased and BAP, TRAP and OCN all decreased in the Ca + D group (p < .05). Training increased distal tibia volumetric BMD (+1.9 ± 2.8%), BMC (+2.0 ± 3.1%), and bone strength index (BSI; +4.0 ± 4.0%) and diaphyseal BMC (+1.0 ± 2.2%) and polar stress strain index (SSIp; +0.7 ± 2.1%) independent of Ca + D supplementation (p < .05 for all). When analyzed by season, change in BSI was greater in the Ca + D group as compared to placebo in the summer iteration only (T*G; p < .05). No other effects of supplementation on bone tissue were observed. When categorized by tertile of percent change in BSI, recruits demonstrating the greatest changes in BSI and 25OHD entered training with the lowest levels of 25OHD (p < .05). Over all, these results suggest that Ca + D supplementation reduced some markers of bone formation and resorption and the decline in 25OHD over training in volunteers that started training in the summer was prevented by supplementation. Baseline 25OHD and trajectory may impact bone responses to IMT, but little effect of Ca + D supplementation was observed at the investigated doses.

Higher Protein Density Diets Are Associated With Greater Diet Quality and Micronutrient Intake in Healthy Young Adults

Objective: This study characterized habitual dietary protein intake in healthy young adults entering military service and explored whether diet protein density is associated with diet quality and micronutrient intake. Methods: An FFQ was used to estimate habitual dietary intake and calculate HEI scores in 276 males [mean(SD), age:21.1y(3.8)] and 254 females [age:21.2y(3.7)]. Multivariate-adjusted MANCOVA and ANCOVA models were used to identify associations between protein density quartiles and HEI scores and micronutrient intake. Higher HEI components scores for sodium, refined grains, and empty calories indicate lower intake; higher scores for all other components indicate higher intakes. Results: Mean(SD) energy-adjusted protein intakes were 29.3(3.2), 36.0(1.4), 40.8(1.3), and 47.9(3.9) g/1,000 kcal for protein density quartiles 1-4, respectively. For males, empty calorie scores as well as dark green and orange vegetable scores were higher in quartiles 3 and 4 than 1 and 2 (all, p < 0.05). Scores for total vegetable, dairy, and total protein foods were lower in quartile 1 vs. quartiles 2, 3, and 4 (all, p < 0.05). Sodium scores decreased as quartiles increased (p < 0.001). Total HEI, fruit, whole grains, seafood and plant protein, fatty acids, and refined grain scores did not differ. For females, total HEI, vegetable, and total protein foods scores were higher in quartiles 3 and 4 than 1 and 2 (all, p < 0.05). Empty calorie scores increased as quartile increased (p < 0.05). Dairy scores were higher in quartiles 2, 3, and 4 than 1 (p < 0.05). Whole fruit scores were lowest in quartile 1 (p < 0.05). Whole grain as well as seafood and plant protein scores were higher in quartile 4 vs. 1 (both, p < 0.05). Sodium scores decreased as quartile increased (p < 0.001). Fatty acids scores did not differ. For males and females, micronutrient intakes progressively increased across quartiles with the exception of calcium and vitamin C, (all, p < 0.05). Intakes remained nearly the same when controlled for fruit and vegetable intake. Conclusion: These cross-sectional data suggest that habitually consuming a higher protein density diet is associated with better scores for some, but not all, diet quality components in males, better overall diet quality scores in females, and greater intakes of micronutrients in both male and female healthy, young adults entering military service.

Skeletal responses to an all-female unassisted Antarctic traverse

PURPOSE

To investigate the skeletal effects of the first all-female trans-Antarctic traverse.

METHODS

Six women (mean ± SD, age 32 ± 3 years, height 1.72 ± 0.07 m, body mass 72.8 ± 4.0 kg) hauled 80 kg sledges over 1700 km in 61 days from coast-to-coast across the Antarctic. Whole-body areal bone mineral density (aBMD) (dual-energy X-ray absorptiometry) and tibial volumetric BMD (vBMD), geometry, microarchitecture and estimated mechanical properties (high-resolution peripheral quantitative computed tomography) were assessed 39 days before (pre-expedition) and 15 days after the expedition (post-expedition). Serum and plasma markers of bone turnover were assessed pre-expedition, and 4 and 15 days after the expedition.

RESULTS

There were reductions in trunk (-2.6%), ribs (-5.0%) and spine (-3.4%) aBMD from pre- to post-expedition (all P ≤ 0.046); arms, legs, pelvis and total body aBMD were not different (all P ≥ 0.075). Tibial vBMD, geometry, microarchitecture and estimated mechanical properties at the metaphysis (4% site) and diaphysis (30% site) were not different between pre- and post-expedition (all P ≥ 0.082). Bone-specific alkaline phosphatase was higher 15 days post- than 4 days post-expedition (1.7 μg∙l^-1, P = 0.028). Total 25(OH)D decreased from pre- to 4 days post-expedition (-36 nmol∙l^-1, P = 0.008). Sclerostin, procollagen 1 N-terminal propeptide, C-telopeptide cross-links of type 1 collagen and adjusted calcium were unchanged (all P ≥ 0.154).

CONCLUSION

A decline in aBMD of the axial skeleton may be due to indirect and direct effects of prolonged energy deficit. We propose that weight-bearing exercise was protective against the effects of energy deficit on tibial vBMD, geometry, microarchitecture and strength.

Osseous Remodeling Around Dental Implants

Adequate bone remodeling may be a primary parameter for long-term successful complication-free dental implant treatment. A 1.8-mm osseous thickness around dental implants is thought to be the minimum thickness for adequate vasculature for osteocyte nutrition and function. A dental implant does not provide progenitor cells or angiogenic or osteogenic factors. Thus, the surrounding bone may need to have a 1.8-mm thickness to accommodate the vasculature necessary for nutrients for appropriate remodeling. Additionally, the 1.8-mm dimension may provide for mechanical load resistance. There is no evidence to illustrate the physiologic need for the 1.8-mm dimension. This dimension requirement is based on clinical outcome observations. Basic science research for bone survival around dental implants is needed.