Impact exercise, dietary calcium and growing bone
Abstract
Skeletal strength in old age is more or less the sum of bone acquired during growth and bone lost after growth. Adaptations during growth can lead to greater skeletal competence in old age. We tested the ability of the growing skeleton to adapt to high impact exercise with and without sufficient dietary calcium, using young female rats as models for children. A freefall impact protocol was developed to mimic the effects of children landing from a height onto a hard surface. Rats were dropped 10 times daily from 30cm and 60cm with 11s between drops, 5 days a week for 8 weeks. Drops were executed so that rats landed on all feet simultaneously. Effects of impact from 30cm and 60cm on 6 appendicular bones were examined by mechanical testing and peripheral computed tomography (pQCT). The 30cm drop height was sufficient to increase bone strength and stimulate geometric changes in the shaft areas and densitomic gains in the bone ends, although some changes were increased by greater drop heights. Effects from impact were more pronounced in the forelimbs than in the hindlimbs. Peak vertical ground reaction forces (GRF) from freefall landings were measured in additional rats. GRFs from 30cm, 45cm, and 60cm heights were greater in the fore than the hind limbs. In an additional study, we investigated the effects of a low versus normal calcium diet on growing rats with and without freefall impact from 45cm. Effects from this study were examined in the ulna, and additional measurements on these bones were performed by microcomputed tomography (microCT). The low calcium diet resulted in lower bone mineral density (BMD) but no diminution in bone strength. Effects of adequate calcium and impact loading were independently beneficial for many parameters, although the effects of impact were stronger. Impact loading exerted a compensatory effect in rats receiving the low calcium diet on total and cortical BMD, and trabecular bone volume fraction (BV/TV) of the proximal ulna. Although either impact exercise or adequate calcium was better than neither for the growing rat skeleton, impact exercise improved bone strength with and without adequate dietary calcium.
Degree
Ph.D.
Advisors
Weaver, Purdue University.
Subject Area
Nutrition|Sports medicine
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