Differential response of rat limb bones to strenuous exercise

Abstract

We examined the influence of a strenuous exercise regimen on tibial and metatarsal bones to show not only how the geometric, histological, and mechanical properties of immature bone respond to strenuous exercise but also how long bones within the same limb may respond differentially to exercise. Female Sprague-Dawley rats (8 wk old) were divided randomly into two groups: a sedentary control (n = 15) and an exercised group (n = 15). The exercise intensity was 80-90% of maximum oxygen capacity 5 days/wk for 10 wk. Mechanical properties of tibia and second metatarsus (MT) were determined with three-point bending, and contralateral bones were used for geometric and histological analyses. Length and middiaphyseal cross-sectional geometry of the exercised tibiae were significantly less than controls, but material properties were not different. The exercised tibiae had significantly lower structural properties (e.g., loads at the proportional limit and maximum and energy at failure load). The middiaphyseal dorsal cortex of exercised MT was significantly thicker than controls, but tensile stress at the proportional limit and elastic modulus of exercised MT were significantly less than controls. The average number of osteons and osteocytes per unit area of the tibial middiaphysis was significantly greater in the exercised group--especially in lateral and posterior cortices. The number of osteons and osteocytes per unit area in the MT, however, was significantly less in the exercised group. The differential effects of strenuous exercise on tibia and MT suggest that local loading and bone-specific responses have important roles in modulating the response of immature bone to strenuous exercise.

Comparison of structural, architectural and mechanical aspects of cellular and acellular bone in two teleost fish

“…Structurally, the tissues are easily visibly distinguished from one another by the presence and absence of osteocytes, but are more similar to each other in gross, histological morphology than they are to the more-studied cellular bone types of amniotes. In particular, differences in osteocyte presence and associated canalicular density are striking, even for the cellular boned carp where osteocytes are much less densely packed than those of birds and mammals (424 vs 700-1800cellsmm -2 ) (Li et al, 1991;Skedros, 2005). The low osteocyte density, coupled with the apparent relative scarcity of blood vessels in both tilapia and carp bone, make both fish bone types observed here appear, at lower magnifications, as more solid (less porous) blocks of tissue compared with amniote bone, also suggesting they may have a lower metabolic rate.…”

“…elliptical in shape with major and minor diameters of 10 and 5m, respectively (McCreadie et al, 2004;Hannah et al, 2010)] the area fraction taken by the osteocytic lacunae in carp bones is 1.6%. The osteocytic lacunae (black arrows in Fig.3C,E) in the bones of the carp show distinct canalicular networks interconnecting adjacent lacunae (black arrowhead in Fig.3E); however, their distribution is less dense than in mammals (R.S., personal observation) (Skedros, 2005;Li et al, 1991).…”

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.…”

456 the Response of Trabecular Bone to Physical Activity in Young Sedentary Males

“…The results of animal research has shown that geometric, composition and growth properties may vary in different bones presumably as a function of the different loading histories at a particular site. Li et al (1991) examined the effect of strenuous exercise on the immature bone of rats. They found that the cross-sectional area of two sites differed, with an increase at the second metatarsus and a decrease in the tibia.…”