Abstract

We examined the effect of a strenuous exercise regimen on tibial and metatarsal bones to show not only how the geometric, histological, and mechanical properties of immature bone respond to strenuous exercise but also how long bones within the same limb may respond differentially to exercise. Female Sprague-Dawley rats (8 wk) were divided randomly into 2 groups: a sedentary control and an exercised group. Exercise intensity was 80-90 VO2max 5 d/wk for 10 wk. Mechanical properties of tibia and second metatarsus (MT) were determined with three-point bending. Length and middiaphyseal cross-sectional geometry of exercised tibiae were significantly less than controls, but material properties were not different. Exercised tibiae had significantly lower structural properties (loads at the proportional limit and maximum and energy at failure load). The middiaphyseal dorsal cortex of exercised MT was significantly thicker than controls, but tensile stress at the proportional limit and elastic modulus of exercised MT were significantly less than controls. The average number of osteons and osteocytes per unit area of the tibial middiaphysis was significantly greater in the exercised - especially in lateral and posterior cortices. Number of osteons and osteocytes per unit area in the MT, however, was significantly less in the exercised group. The differential effects of strenuous exercise on tibia and MT suggest that local loading and bone-specific responses have important roles in modulating the response of immature bone to exercise. Verf.-Ref.