The effects of eccentric training on muscle-bone function

Abstract

The purpose of this study was to determine if eccentric exercise training can attenuate or prevent bone loss associated with estrogen-deficiency in the mouse model. A secondary purpose was to determine if any bone changes were due to changes in bone mechanical properties, rather than bone quantity. Four groups of mice were used to investigate the effects of high-intensity exercise training on the estrogen-deficient mouse. An aging control group (CONTROL) was used to control for the effects of nerve cuff implantation, while a sham ovariectomy group (SHAM) served as an estrogen-intact control. One-half of the ovariectomized mice (OVX) underwent training via 30 eccentric contractions of the anterior coral muscles at 150% of peak isometric torque (OVX+TRAIN) every third day for 8 weeks. Results demonstrate that the eccentric exercise regimen used in this study elicited a training effect in the relevant skeletal muscles, as indicated by a 20.1% increase in peak isometric torque and a 7.5% increase in peak eccentric torque between bouts #1 and #18. In vivo bone testing showed mixed results for bone responses across the 8 week time course. The trained group showed greater radial growth at the proximal tibia in the left (trained) limb than other groups. This radial growth occurred despite no changes in cortical area. Both total and cortical bone mineral density (BMD) at the left proximal tibia were lower in the OVX+TRAIN group than in the other groups. Despite no significant changes in BMD at the mid-shag tibia, mechanical testing at this site showed greater tibiae stiffness in the exercised bone than that of the OVX group (+28.5%). No significant differences were found in tibial ultimate load to fracture, ultimate strength or modulus of elasticity. In summary, the results from this study indicate that eccentric exercise training every third day for 8 weeks can promote skeletal muscle gains and partially offset bone BMD loss at the proximal tibia associated with estrogen-deficiency in the mouse model. Despite no changes in mid-shag BMD, mean stiffness of the OVX+TRAIN group was significantly greater than that of the OVX group.