Bone Mineral Density and Body Composition in Ultra-Endurance Running
Mario Buchs
UESCA Ultra Running Certification
April 2026

 

Introduction

Ultra-endurance running places unique physiological demands on the human body, characterised by prolonged mechanical loading, high training volumes, and significant energetic stress. While running is traditionally considered a weight-bearing activity beneficial for bone health, emerging evidence suggests that endurance athletes may not always demonstrate optimal bone mineral density (BMD), particularly when high training loads are combined with inadequate recovery or energy intake.

The use of DEXA scan has become increasingly prominent in both clinical and performance settings, allowing for precise assessment of bone density alongside body composition variables such as lean mass, fat mass, and visceral adipose tissue. This provides a more comprehensive understanding of an athlete’s physiological status than traditional measures such as body weight or body mass index.

This paper explores the relationship between ultra-endurance running and bone health through a combination of existing literature and a longitudinal case study. Serial DEXA scans were collected across three ultra-endurance events within a single competitive season, with consistent measurement timing and recovery protocols. The aim is to evaluate whether repeated ultra-endurance stress negatively impacts bone density, and to better understand the short-term and longer-term fluctuations in body composition associated with racing and recovery.

It is important to note that the subject has a prior diagnosis of osteoporosis. This is relevant when interpreting bone mineral density outcomes, as baseline bone health may influence both the magnitude and direction of adaptation. As such, findings from this case study should be interpreted within the context of a higher-risk population.

This case study is further contextualised by the subject’s history of two sacral stress fractures sustained over a four-year period. These injuries prompted a more focused investigation into bone health, training load, and recovery strategies, ultimately leading to the implementation of regular DEXA monitoring as both a performance and health management tool.

 

DEXA Scanning in Performance and Health

DEXA scanning is widely regarded as the gold standard for assessing body composition and bone mineral density due to its high precision and reproducibility. The scans in this case study were performed using a clinically validated platform capable of simultaneously measuring bone, lean tissue, and fat mass with high-resolution imaging.

DEXA provides several key outputs relevant to endurance athletes:

• Bone mineral density (g/cm²), a key indicator of bone strength and fracture risk 
• Lean mass, representing muscle and non-fat tissue 
• Fat mass and body fat percentage 
• Visceral adipose tissue (VAT), associated with metabolic health 

This level of detail allows practitioners to move beyond simplistic metrics and gain deeper insight into how training, nutrition, and recovery influence overall physiology.

 

Bone Physiology and Mechanical Loading

Bone is a dynamic tissue that continuously remodels in response to mechanical and metabolic stimuli. This process is governed by two key cell types: osteoblasts, which are responsible for bone formation, and osteoclasts, which drive bone resorption. The balance between these opposing processes determines overall bone mineral density.

Mechanical loading stimulates osteoblast activity, promoting bone formation. However, when physiological stress, inadequate energy availability, or hormonal disruption are present, osteoclast activity may dominate, leading to reduced bone density over time. This balance is particularly relevant in ultra-endurance athletes, where high training loads and energy demands can influence bone turnover. Mechanical loading is one of the primary drivers of bone adaptation. High-impact, multidirectional forces, such as those encountered in resistance training or plyometric activity = are particularly effective at stimulating increases in BMD. In contrast, ultra-endurance running involves repetitive, relatively low-impact loading over extended durations.

While this provides some osteogenic stimulus, it may not be sufficient to maximise bone density. Furthermore, the high energetic demands of ultra-endurance training can influence hormonal function and bone turnover, particularly when energy availability is inadequate.

 

Methods: Case Study Design

This case study utilised serial DEXA scans collected across three ultra-endurance races in 2025: UTA100 (May = 100km with 4400m of elevation gain), Elephant Miler (July = 100milesn with 9000m of elevation gain), and Coast to Kosciuszko (November = 240km with 5500m of elevation gain). Scans were conducted at three consistent time points for each event:

1. Pre-race 
2. Within several days post-race 
3. Approximately five days post-race 

This standardised timing allows for differentiation between acute physiological responses and short-term recovery adaptations. 

Recovery strategies were consistent across all races and included:

• Daily cold water immersion (~6 minutes) 
• Relative rest 
• A whole-food, plant-based (vegan) diet 

While not experimentally controlled, the consistency of these variables strengthens the reliability of observed trends.

In addition to endurance training, the subject performed approximately three resistance training sessions per week. This is a relevant factor, as resistance and high-load training are known to provide an osteogenic stimulus and may contribute to the maintenance of bone mineral density.

 

Results

Body Composition

Across all three races, a consistent pattern was observed:

• Lean mass increased immediately post-race 
• Fat mass and body fat percentage decreased post-race 
• These changes partially reversed within 5–7 days 

These fluctuations are likely acute rather than structural. Increases in lean mass may reflect inflammation, fluid shifts, and glycogen replenishment rather than true muscle hypertrophy. Similarly, reductions in fat mass are likely transient and influenced by energy expenditure and hydration status.

Interestingly, later-season data demonstrated greater stability, suggesting potential adaptation to cumulative training stress.

 

Visceral Fat

Visceral adipose tissue increased acutely following each race before returning toward baseline within days. This transient response may be linked to:

• Systemic inflammation 
• Hormonal stress responses 
• Fluid redistribution 

No long-term upward trend was observed, indicating no deterioration in metabolic health across the season.

 

Bone Mineral Density

Bone mineral density remained stable across the full observation period:

• Baseline: 1.115 g/cm² 
• Final: 1.141 g/cm² 

Although small fluctuations occurred following individual races, there was no evidence of progressive decline. In some instances, BMD increased post-race before returning to baseline, suggesting short-term variability rather than structural change.

 

Discussion

Stability of Bone Density

The stability of BMD observed in this case study challenges the assumption that high-volume endurance training inherently leads to bone loss. Instead, it suggests that under appropriate conditions(particularly consistent recovery and nutrition), bone health can be maintained despite significant training loads.

However, it is important to recognise that running alone may not be sufficient to increase bone density. The absence of a progressive increase in BMD supports existing literature indicating that repetitive endurance loading provides a limited osteogenic stimulus compared to resistance or impact-based training.

The maintenance of bone mineral density observed in this case may be partially explained by the inclusion of regular resistance training. Unlike endurance running, which provides repetitive but relatively low-impact loading, resistance training introduces higher strain magnitudes that are known to stimulate osteoblast activity and support bone formation. This highlights the importance of training diversity in endurance athletes, particularly those at increased risk of compromised bone health.

It should be acknowledged that the inclusion of resistance training represents a confounding variable, limiting the ability to attribute bone density outcomes solely to ultra-endurance running.

 

Role of Cold Water Immersion

Cold water immersion (CWI) formed a consistent component of recovery across all races. While widely used to reduce soreness and perceived fatigue, its effects on musculoskeletal adaptation are complex.

Research suggests that CWI may attenuate some training adaptations by reducing inflammatory signalling pathways associated with muscle growth. This raises important considerations for its long-term use in performance settings.

In relation to bone health, evidence is less conclusive but indicates that cold exposure can influence bone metabolism. Studies have shown that cold exposure can alter mineral concentrations within bone and affect hormonal regulators of bone remodelling. Additionally, cold exposure may influence bone perfusion and metabolic activity through reduced blood flow and sympathetic nervous system activation .

Some evidence also suggests that cold exposure may have both positive and negative effects on bone depending on duration and context. While short-term or localised cryotherapy may support bone healing and regeneration, prolonged or chronic exposure has been associated with reductions in bone mass in certain models.

Taken together, these findings suggest that the short duration, recovery focused cold water immersion used in this case is unlikely to negatively impact bone density, but its long-term effects remain an area for further research.

 

Energy Availability and RED-S

A key factor influencing bone health in endurance athletes is energy availability. Chronic energy deficiency can impair hormonal function, reduce bone formation, and increase injury risk.

This is central to Relative Energy Deficiency in Sport, a condition that highlights the systemic consequences of inadequate energy intake relative to training demands.

In this case study, the use of a nutrient dense wholefood vegan diet, combined with structured recovery, may have supported adequate energy availability and contributed to the maintenance of bone density.

 

Practical Implications

From a coaching and applied perspective, several key insights emerge:

1. Bone Health is Multifactorial

Ultra-running alone does not determine bone density. Nutrition, recovery, and training diversity all play critical roles.

2. Strength Training is Essential

To optimise bone health, endurance athletes should incorporate resistance and impact-based training to provide sufficient osteogenic stimulus.

3. Interpret DEXA Data Carefully

Post-race fluctuations in lean mass, fat mass, and visceral fat are often transient and influenced by hydration and inflammation.

4. Use Recovery Strategically

Cold water immersion may support short-term recovery, but its long-term use should be considered carefully within the context of overall adaptation.

5. Monitor Long-Term Trends

DEXA is most valuable when used longitudinally to identify trends rather than isolated changes.

 

Conclusion

Ultra-endurance running presents complex physiological challenges, with potential implications for both performance and long-term health. This case study demonstrates that bone mineral density can remain stable across a competitive season, despite repeated exposure to extreme endurance stress.

However, this stability is likely dependent on a combination of factors, including adequate nutrition, structured recovery, and training diversity. Ultra-running alone does not appear sufficient to optimise bone health, highlighting the importance of a holistic approach.

For coaches and athletes, the key takeaway is clear: maintaining bone health in endurance sport requires more than simply accumulating miles. It requires a deliberate integration of strength training, appropriate fuelling, and informed recovery strategies to support both performance and longevity.

 

References

Bleakley, C. M., & Davison, G. W. (2010). What is the biochemical and physiological rationale for using cold-water immersion in sports recovery? Sports Medicine, 40(1), 55–70.

Frontiers in Physiology. (2021). Effects of cold exposure on bone metabolism markers. Frontiers in Physiology. https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2021.731523/full

Hologic Inc. (n.d.). Horizon DXA System. Retrieved from https://www.hologic.com.au/en-au/products/horizon-dxa-system

Roberts, L. A., Raastad, T., Markworth, J. F., et al. (2015). Post-exercise cold water immersion attenuates acute anabolic signalling and long-term adaptations in muscle to strength training. The Journal of Physiology, 593(18), 4285–4301.

Sims, S. T., & Heather, A. K. (2018). Myths and methodologies: Reducing scientific design ambiguity in studies comparing sexes and/or menstrual cycle phases. Experimental Physiology, 103(10), 1309–1317. (useful for RED-S/energy availability context)

Wang, Z., et al. (2021). Effects of cold-water immersion on bone mineral metabolism in rats. International Journal of Molecular Sciences, 22(10), 5432. https://pmc.ncbi.nlm.nih.gov/articles/PMC8143118/

Zhang, Y., et al. (2024). The effects of cold exposure on bone remodeling and skeletal health: A review. Biomedicines, 12(9), 2045. https://www.mdpi.com/2227-9059/12/9/2045

Mountjoy, M., et al. (2018). IOC consensus statement on relative energy deficiency in sport (RED-S). British Journal of Sports Medicine, 52(11), 687–697.

 

Research & Findings by Mario Buchs
UESCA-certified Ultrarunning Coach
Healthetica Coaching — healtheticacoaching.com