Bone Mineral Density in Mountain, Road Cyclists and Untrained Controls: Exercise, Diet and Hormones

Purpose: The aim of the study was to compare bone mineral density (BMD) in the lumbar spine (LS_BMD) and the femoral neck (F_BMD) in male road cyclists (RC n = 39), mountain cyclists (MC n = 30) and controls (C n = 27) and to determine the factors associated with BMD in the same group of participants. Methods: BMD, fat mass (FM) and fat-free mass (FFM) were measured using DXA. Calcium intake (Cal), exercise energy expenditure (EEE) and energy availability (EA) were assessed using self-reported questionnaires. Samples for circulating hormones were also obtained. VO_2max was estimated by a cycloergometric test. Results: After adjustment for body mass, in cyclists LS_BMD (RC 0.98 ± 0.12; MC 0.98 ± 0.10 g/cm²) was significantly lower than in C (1.11 ± 0.10; p < .001), while F_BMD resulted in no significant difference in cyclists compared to C (p = 0.213). EA (kcal/FFM/day) was different in cyclists and in C (p < .05). In C, EEE and EA were positively associated with LS_BMD (R = 0.561, R = 0.656, respectively, p < .01), whereas only EA was associated with F_BMD (R = 0.554, p < .05); a positive association between EA and F_BMD was found in MC (R = 0.464, p < .05). A negative relationship between VO_2max and LS_BMD in RC (R = -0.418, p < .05) and a positive one between EEE and LS_BMD in MC were found (R = 0.605, p < .001). CaI, free testosterone and cortisol were unrelated to BMD. Conclusion: Both the RC and MC had lower LS_BMD than C, whereas no difference was found between the two groups of cyclists. The factors associated with BMD are manifold, vary in relation to the measurement site and are likely different in RC, MC and C.