Professional jockeys routinely undertake chronic weight-management practices to meet racing weight requirements. These practices may compromise energy availability, alter body composition and contribute to poor bone health, with a high prevalence of low bone mineral density (BMD) reported in this population (1,2). Preservation of lean mass is a key objective of contemporary sports nutrition strategies for weight-restricted athletes; however, longitudinal relationships between lean mass and skeletal health in professional jockeys remain poorly understood. This study investigated the longitudinal association between appendicular lean mass index (ALMI) and lumbar spine BMD in professional male jockeys receiving individualized sports science support under free-living conditions.
Repeated dual-energy X-ray absorptiometry assessments collected between 2021 and 2025 were retrospectively analysed. Thirty-two professional male jockeys contributed 102 repeated assessments (median 3 scans per jockey; range 1–5). Lumbar spine BMD (g/cm²) was the outcome variable and ALMI (kg/m²) the primary predictor. Age-adjusted linear mixed-effects models with random intercepts for jockey were used to account for repeated measurements. A primary model examined the overall association between ALMI and BMD. A secondary model decomposed ALMI into between-person and within-person components to distinguish differences between jockeys from longitudinal changes occurring within individual jockeys over time.
The primary model identified no statistically significant association between ALMI and lumbar spine BMD (p = 0.091). In the decomposed model, the between-person ALMI effect was not significant (β = 0.031, SE = 0.051, p = 0.549). However, a significant inverse within-person association was observed (β = -0.052, SE = 0.024, p = 0.032), indicating that occasions when a jockey's ALMI exceeded his own long-term average were associated with lower lumbar spine BMD. Age was not significantly associated with BMD (p = 0.295).
These findings suggest that cross-sectional relationships between lean mass and bone health may not reflect longitudinal within-athlete changes. In professional jockeys exposed to chronic weight-management practices, changes in lean mass and skeletal health may not occur in parallel. Further research is required to determine the nutritional and physiological mechanisms underpinning this association and to inform body-composition management strategies aimed at preserving musculoskeletal health in weight-restricted athletes.