The purpose of this study was to estimate the effects of intense and regular physical activity on locomotor system modifications. Tennis, with its unilateral solicitations, allows a more precise examination of specific localized development. Ten professional tennis players were compared with sedentary age-matched students. Muscular modifications were observed, mainly in the forearm circumference. The dominant side forearm circumference was 13% larger than the opposite side. Asymmetry was less in the upper arm and insignificant in the thorax and vertebra. Deep modifications in bone mineral content (BMC) were investigated by isotopic techniques, based on differential photon attenuation in bone and soft tissue of the forearm. Bone density was markedly increased in professional tennis players. Even in the nondominant side, radius BMC was 1.18 g HA/cm, 15% higher than in sedentary control students. The difference was yet larger in the dominant mid-radius, reaching 1.47 g HA/cm. The same differences were observed for the ulna and involved both cortical and trabecular bone. In the control group of sedentary students, no significant difference was noted between the two upper limbs. This study clearly demonstrates the positive correlation between exercise and bone mineralization. The precise mechanical constraints optimizing the favorable effect in the most efficient way should be studied.