Elevated Mechanical Loading When Young Provides Lifelong Benefits to Cortical Bone Properties in Female Rats Independent of a Surgically Induced Menopause

Abstract

Exercise that mechanically loads the skeleton is advocated when young to enhance lifelong bone health. Whether the skeletal benefits of elevated loading when young persist into adulthood and after menopause are important questions. This study investigated the influence of a surgically induced menopause in female Sprague-Dawley rats on the lifelong maintenance of the cortical bone benefits of skeletal loading when young. Animals had their right forearm extrinsically loaded 3 d/wk between 4 and 10 weeks of age using the forearm axial compression loading model. Left forearms were internal controls and not loaded. Animals were subsequently detrained (restricted to cage activities) for 94 weeks (until age 2 years), with ovariectomy (OVX) or sham-OVX surgery being performed at 24 weeks of age. Loading enhanced midshaft ulna cortical bone mass, structure, and estimated strength. These benefits persisted lifelong and contributed to loaded ulnas having greater strength after detraining. Loading also had effects on cortical bone quality. The benefits of loading when young were not influenced by a surgically induced menopause because there were no interactions between loading and surgery. However, OVX had independent effects on cortical bone mass, structure, and estimated strength at early postsurgery time points (up to age 58 weeks) and bone quality measures. These data indicate skeletal loading when young had lifelong benefits on cortical bone properties that persisted independent of a surgically induced menopause. This suggests that skeletal loading associated with exercise when young may provide lifelong antifracture benefits by priming the skeleton to offset the cortical bone changes associated with aging and menopause.

Does Physical Activity in Adolescence Have Site-Specific and Sex-Specific Benefits on Young Adult Bone Size, Content, and Estimated Strength?

“…Based on this evidence, the level of PA needed to maintain bone size and strength benefits, obtained by a physically active lifestyle in adolescence, is likely less than the activity needed for structural adaptation. Previous observations from retired athletes and animal experiments support this concept. Experimental studies have indicated lifelong benefits in cortical bone from loading stimulus obtained during skeletal growth .…”

“…Previous observations from retired athletes and animal experiments support this concept. Experimental studies have indicated lifelong benefits in cortical bone from loading stimulus obtained during skeletal growth . Altogether, this evidence suggests that developing larger cortex during growth may provide lifelong antifracture benefits by priming the skeleton to offset the cortical bone thinning and trabecularization of the endocortical bone associated with aging .…”

Multiscale analysis of morphology and mechanics in tail tendon from the ZDSD rat model of type 2 diabetes

“…All tests here took place in fluid. In other studies using this technique to quantify collagen nanoscale morphology, shifts in the D-spacing distribution have been noted following estrogen deficiency (Wallace et al 2010b; Warden et al 2013) and with Osteogenesis Imperfecta (Wallace et al 2011; Kemp et al 2012) in multiple tissues, but not between different tissue types in healthy mice (Wallace et al 2010a), or between male and female mice. This study demonstrated that diabetic tendons had a distribution of fibril D-spacings that was narrower versus control (Figure 2).…”

“…Although postulated to have a singular value of 67 nm (Hodge and Petruska 1963), recent work has shown that D-spacing exists with a distribution of values (Wallace et al 2010a). This distribution changes with several disease states in bone (Wallace et al 2010a; Wallace et al 2011; Warden et al 2013), skin (Fang et al 2012) and tendon (Kemp et al 2012), suggesting a metric that may represent a diagnostic option for diseases in collagen-based tissues. To put functional meaning behind this measure of nanoscale morphology, recent work focused on mechanically probing collagen fibrils (Kemp et al 2012; Wallace et al 2012).…”

Bone fatigue and its implications for injuries in racehorses

“…Beneficial effects of the early introduction of exercise regimens in growing horses are well documented [98][99][100]. Bone is most adaptable prior to maturity, and the benefits of early adaptation are long lasting [101][102][103].…”