title: Adaptations of immature trabecular bone to moderate exercise: geometrical, biochemical, and biomechanical correlates.
abstract: Strenuous endurance exercise can adversely affect the mechanical integrity of immature bone, but it is unclear whether a more moderate exercise regimen would have a positive effect. Thus, to investigate the response of immature trabecular bone to moderate exercise, we randomly assigned female Sprague-Dawley rats (8 weeks old) to either a basal-control, exercise, or age-matched control group. The basal-control rats were killed at 8 weeks of age, while the other two groups were killed at 18 weeks of age. Between 8 and 18 weeks, one group remained sedentary, while another group was trained progressively on a motor-driven treadmill at a moderate level of intensity. Rat femoral necks (FN) were tested in cantilever bending to failure, and the sixth lumbar vertebral bodies (L6) were compressed to 50% of their initial height. Both tissues were analyzed for calcium, hydroxyproline, and collagen-crosslinking concentrations, and for changes in geometry. The adrenal mass per unit body mass was significantly greater in the exercised group, compared to the age-matched controls. L6 calcium content, compressional stress, and elastic modulus were significantly less in the exercise group as compared to the age-matched control group. Nonreducible collagen crosslinks (hydroxylysylpyridinoline [HP] and lysylpyridinoline [LP]) were significantly greater in the older exercise and age-matched control L6 and FN. In the weightbearing FN--but not L6--the LP concentration of the exercise group was significantly greater than the age-matched controls.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiological Science, UCLA 90024-1568.
authors.forename: G J
authors.initials: GJ
authors.lastname: Salem
authors.forename: R F
authors.initials: RF
authors.lastname: Zernicke
authors.forename: D A
authors.initials: DA
authors.lastname: Martinez
authors.forename: A C
authors.initials: AC
authors.lastname: Vailas
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001696:Biomechanical Phenomena; D001842:Bone and Bones / Q000737:chemistry / Q000473:pathology / Q000502:physiology*; D005260:Female; D005272:Femur Neck; D008159:Lumbar Vertebrae; D010805:Physical Conditioning, Animal; D051381:Rats; D017207:Rats, Sprague-Dawley