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1 Department of Health and Kinesiology and 2 Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843
Our purpose
was to determine the effects of a mechanical loading intervention on
mass, geometry, and strength of rat cortical bone during a period of
disuse concurrent with calcium deficiency (CD). Adult female rats were
assigned to unilateral hindlimb immobilization, immobilized-loaded, or
control (standard chow, 1.85% calcium) treatments. Both immobilized
groups were fed a CD rat chow (0.01% calcium) to induce high bone
turnover. Three times weekly, immobilized-loaded rats were subjected to
36 cycles of 4-point bending of the immobilized lower leg. After 6 wk,
the immobilized rats exhibited decreased tibial shaft bone mineral
density (
12%), ultimate load (
19%), and stiffness
(
20%; tested in 3-point bending to failure) vs. control rats.
Loading prevented this decline in bone density and attenuated decreases
in ultimate load and stiffness. Elastic modulus was unaffected by
disuse or loading. Bone cross-sectional area in the immobilized-loaded
rats was equivalent to that of control animals, even though
endocortical resorption continued unabated. On the medial periosteum,
percent mineralizing surface doubled vs. that in immobilized rats. This
loading regimen stimulated periosteal mineralization and maintained
bone mineral density, thereby attenuating the loss in bone strength
incurred with disuse and concurrent calcium deficiency.
bone density; adult rats; disuse; mechanical properties
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