Effects of eccentric exercise training on cortical bone and muscle strength in the estrogen-deficient mouse

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Abstract
The purpose of this study was to determine whether eccentrically biased exercise training could attenuate changes in muscle and bone function associated with estrogen deficiency in the mouse model. Four groups of ICR mice were used: control (Con), sham ovariectomized (Sham), ovariectomized (OVX), and ovariectomized + high-force resistance training (OVX+Train). All groups except Con were implanted with a nerve cuff surrounding the peroneal nerve to stimulate the left ankle dorsiflexors. Training consisted of 30 stimulated eccentric contractions of the left ankle dorsiflexors at ∼150% of peak isometric torque every third day for 8 wk. After the training period, groups were not significantly different with regard to peak torque or muscle size. However, the tibial midshaft of the trained leg in the OVX+Train mice exhibited greater stiffness (+15%) than that in the untrained OVX mice, which could not be explained by changes in cross-sectional geometry of the tibia. Scaling of bone mechanical properties to muscle strength were not altered by ovariectomy or training. These data indicate that eccentric exercise training in adult mice can significantly increase bone stiffness, despite the absence of ovarian hormones.