High impact physical training is beneficial for bone structure and mineralization and typically results in increased levels of bone turnover markers. However, the acute effects of a single exercise session on bone markers are unclear. In adults, inconsistent results have been demonstrated following high impact exercise. In children, there is a paucity of data in this area. PURPOSE: To investigate the acute response of bone turnover markers to an exercise session consisting of high mechanical loading in boys and men. METHODS: Participants underwent a protocol of plyometric jumping exercises (total 144 jumps). Venous blood samples were collected pre, 5 minutes post-, 1 hour post- and 24 hours post-exercise session to measure bone-specific alkaline phosphatase (BAP), amino-terminal cross-linking telopeptide (NTx), osteoprotegrin (OPG) and receptor activator of nuclear factor kb ligand (RANKL). RESULTS: Boys had higher BAP levels, with an increase 24 hours post-exercise (111.9±29.2 vs. 137.6±36.3 μg/L, respectively), which was not observed in the men (31.4±11.1 vs. 33.3±10.5 μg/L, respectively). NTx levels were higher in boys, with a greater increase over time in boys than in men (boys: 48.7±13.7 vs. 58.8±16.7 nM BCE pre- and 24 hours post-exercise, respectively; men: 21.7±5.4 vs. 19.4±5.0 NM BCE pre- and 24 hours post-exercise, respectively). OPG and RANKL levels were similar in boys and men before and after exercise, with no change over 24 hours. CONCLUSIONS: These results indicate that even one session of exercise stimulates bone turnover, as reflected in the increase in both BAP and NTx values, in boys (but not men) within 24 hours.