Bone modeling response to voluntary exercise in the hindlimb of mice

Abstract

The functional adaptation of juvenile mammalian limb bone to mechanical loading is necessary to maintain bone strength. Diaphyseal size and shape are modified during growth through the process of bone modeling. Although bone modeling is a well-documented response to increased mechanical stress on growing diaphyseal bone, the effect of proximodistal location on bone modeling remains unclear. Distal limb elements in cursorial mammals are longer and thinner, most likely to conserve energy during locomotion because they require less energy to move. Therefore, distal elements are hypothesized to experience greater mechanical loading during locomotion and may be expected to exhibit a greater modeling response to exercise. In this study, histomorphometric comparisons are made between femora and tibiae of mice treated with voluntary exercise and a control group (N = 20). We find that femora of exercised mice exhibit both greater bone growth rates and growth areas than do controls (P < 0.05). The femora of exercised mice also have significantly greater cortical area, bending rigidity, and torsional rigidity (P < 0.05), although bending and torsional rigidity are comparable when standardized by bone length. Histomorphometric and cross-section geometric properties of the tibial midshaft of exercised and control mice did not differ significantly, although tibial length was significantly greater in exercised mice (P < 0.05). Femora of exercised mice were able to adapt to increased mechanical loading through increases in compressive, bending, and torsional rigidity. No such adaptations were found in the tibia. It is unclear if this is a biomechanical adaptation to greater stress in proximal elements or if distal elements are ontogenetically constrained in a tradeoff of bone strength of distal elements for bioenergetic efficiency during locomotion.

Effects of Different Swimming Exercise Intensities on Bone Tissue Composition in Mice: A Raman Spectroscopy Study

“…[1][2][3][4] Due to the lack of bone mechanical loadings, reduced osteoid and mineralizing surfaces and decreased bone formation rate have been reported in space flight experiments, 5 and a similar effect of bone mass loss has been reported in scuba divers. 6 Physical training increases the cancellous bone and osteoinductive activity due to an increase of bone morphogenic proteins (BMPs), which decreases bone resorption and increases bone formation.…”

Differential Adaptive Response of Growing Bones From Two Female Inbred Mouse Strains to Voluntary Cage‐Wheel Running

“…The smaller outer bone size in B6‐exercise femora was opposite to expectations that exercise should be associated with an anabolic response,23 which motivated the replication of the study with five additional mice per group and strain. The only other known voluntary cage‐wheel running study reported in growing B6 female mice femora showed more than a doubling of periosteal area following 4 weeks of running 24. However, these mice had access to the cage wheel between 7 and 11 weeks of age.…”

Allen's Rule Revisited: Temperature Influences Bone Elongation During a Critical Period of Postnatal Development

“…The early ontogeny aspect of the study is important to highlight because of varied outcomes in the literature. Results range from reduced limb length with exercise (Kiiskinen, 1977;Li et al, 1991;Bourrin et al, 1994;Reich et al, 2005), to no effect (Nyska et al, 1995;Niehoff et al, 2004;Fritton et al, 2005;Hamrick et al, 2006), to increased limb length with exercise (Beyer, 1896;Adams, 1938;Buskirk et al, 1956;Tomljenovic Borer and Kuhns, 1977;Swissa-Sivan et al, 1989;Losos et al, 2001;Iwamoto et al, 2004;Plochocki et al, 2008;Serrat et al, 2010). Although nutrition, trauma, pathology, sex, severity, and duration of exercise are all potential factors that might explain some of the discrepancies among these studies (particularly the reduced limb growth) (Rogol et al, 2000;Forwood, 2008), much of the remaining variation could be explained by simply examining the age of the subjects.…”