Effects of Single, Maximal Intensity Exercise Unit on Selected Markers of Bone and Connective Tissue Turnover in Young Men

Background/Objectives: Bone tissue undergoes continuous remodelling processes that are closely controlled by mechanical stimuli and metabolic as well as inflammatory factors. Although the beneficial effects of regular physical activity on skeletal health are well documented, the response of bone turnover markers to a single maximal intensity exercise—particularly depending on training level—still remains ambiguous. The aim of the study was to assess the effect of a single physical exercise unit at maximum intensity on changes in selected biochemical markers specific for bone tissue, connective tissue remodelling and systemic stress response in young men. Methods: The study comprised 34 healthy men aged 20–25 years, divided into two groups: experimental (training, n = 15) and control (non-training, n = 19). The test was performed on a mechanical treadmill with a gradually increasing load (until subjective feeling of fatigue). Blood samples were collected before and 60 min following the test, and then assessed for the concentration of selected bone turnover markers, including bone-specific alkaline phosphatase (BSP), C-terminal telopeptide of type I collagen (CTX-I), deoxypyridinoline (DPD), hydroxyproline (GEN HYP) and haptoglobin (HPT). Results: In the group of training individuals, a significant decrease in BSP concentration was observed after physical exercise (p = 0.003). CTX-I concentration was significantly lower in training individuals compared to their non-training peers, regardless of measurement time (p < 0.001). Furthermore, a significant increase in GEN HYP concentration was observed after exercise in both groups (p = 0.033). For the remaining analysed markers, including DPD and HPT, no significant changes were demonstrated post-exercise. Conclusions: A single bout of maximal intensity exercise induces short-term, marker-specific changes in bone turnover dependent on training level, which reflect an early metabolic response of the musculoskeletal system rather than direct structural adaptation of the bone tissue.