Abstract
Mechanical loading of the skeleton is essential for the development and maintenance of bone mass. Non–weight-bearing sports, such as cycling, lack substantial mechanical loading, and, therefore, provide little benefit for bone. Indeed, this thesis revealed a high prevalence of low bone mineral density (BMD) among elite cyclists at different stages of a professional cycling career. Low BMD was also associated with an increased fracture incidence during the active career. Consistent predictors of low BMD in elite cyclists included a lack of prior participation in bone-specific mechanical loading activities, along with markers of low energy availability, such as serum total triiodothyronine (T3) levels and body mass index (BMI). In addition, high-resolution peripheral quantitative computed tomography (HR-pQCT) revealed a high prevalence of low volumetric BMD along with impairments in bone microarchitecture and geometry in a substantial portion of elite cyclists.
We subsequently showed that multi-directional jumping exercise combined with collagen supplementation during the off-season period is both feasible and effective in preserving BMD at the hip region in elite cyclists. However, another study in this thesis showed that the serum marker of bone formation procollagen type I N propeptide (P1NP) increased following brief jumping exercise, but with no further increase following collagen supplementation when compared to a placebo. Additionally, our findings indicate that measuring serum P1NP concentrations in the acute post-exercise period is not a suitable strategy for assessing the direct impact of exercise on bone formation, and that more prolonged measurement periods (days to weeks) are likely required. Finally, we showed that even a single serving of dairy with breakfast already improves postprandial bone metabolism, mainly by the inhibition of bone resorption.
Defence date: 19/09/2025
HAN University of Applied Sciences, Nijmegen, the Netherlands
