Relative effects of exercise training and alendronate treatment on skeletal muscle function of ovariectomized rats.

OBJECTIVE

Increased physical activity and bisphosphonate treatment are both effective in reducing the risk of fracture in postmenopausal women. Physical activity reduces the risk of fracture by improving both bone and skeletal muscle strength. The effects of bisphosphonates have primarily been evaluated on bone. In this study the authors investigated the combined effects of increased physical activity and bisphosphonate treatment on skeletal muscle function using an animal model of postmenopausal osteoporosis.

DESIGN

Seven-month-old ovariectomized rats were assigned to one of four combinations of physical activity treatment (sedentary or endurance running) and alendronate treatment (vehicle or 0.015 mg/kg alendronate, two treatments per week). After 14 weeks slow (soleus) and fast (extensor digitorum longus) muscles were isolated from each animal and electrically stimulated for evaluation of twitch, low-frequency, and tetanic force and resistance to fatiguing stimulation.

RESULTS

Exercise training reduced body mass, increased soleus and extensor digitorum longus muscle mass, increased soleus tetanic force, reduced the twitch contraction time of the soleus and extensor digitorum longus, and facilitated relaxation of the soleus during fatiguing stimulation. Bisphosphonate treatment had no independent effect on muscle function and interacted with training for only a single variable (twitch half-relaxation time).

CONCLUSIONS

Endurance training increased muscle mass in ovariectomized rats and had subtle effects on slow and fast muscle function. Alendronate treatment, at a dosage previously shown to improve bone strength in ovariectomized rats, neither blunted nor enhanced these training adaptations and had no independent effect on muscle contractility.