Does Weight-bearing Exercise Affect Non-weight-bearing Bone?

It was previously reported that weight-bearing exercise increases femur periosteal formation in 3-year-old, 230 kg cross-bred sows. To determine if this weight-bearing exercise also stimulated non-weight-bearing bone, bone formation in the seventh rib from these same sows was measured histomorphometrically on the periosteal, endocortical, and osteonal envelopes. The sows were randomly assigned by body weight to basal (B, n = 6), control (C, n = 7), or trained (T, n = 7) groups. After 3 weeks of exercise adaptation, T walked on a treadmill for 17 weeks at 5 km/h, 20 minutes/day, 5 days/week, at 5% grade. Groups were sacrificed initially (B) or after 20 weeks (C and T). Periosteal mineral apposition rate (MAR) was calculated over 136 days. Osteonal and endocortical MAR were calculated over the 14 days prior to sacrifice. There were no effects of exercise on the periosteal or endocortical percentage double-labeled surface (dLS/BS), osteonal remodeling frequency (N.dL.On/B.Ar), or MAR in any bone envelope of the rib. In conclusion, weight-bearing exercise sufficient to stimulate periosteal formation in the femur did not activate formation in the rib. Bone response to weight-bearing exercise appears to be specific to the loaded bones.