Physical inactivity is a major contributor to ovariectomy-induced sarcopenia.

Since the mechanism(s) underlying menopause-related sarcopenia remain unknown we aimed to investigate the role of physical inactivity in its etiology. Ovariectomized and sham-operated rats were allocated into 2 experimental groups: (1) sedentary-standard housing; and (2) exercise-housed with running wheel. After a 9-month experimental period, soleus muscle structure and biochemical properties were analyzed. No differences existed in muscle fibre size or ultrastructure between sedentary sham and ovariectomized animals housed in standard conditions. In the exercise groups, average daily running distance was 10-fold less in ovariectomized compared to sham-animals. Further, in exercised animals, soleus fibre size was smaller in ovariectomized compared to sham-animals. Nonetheless, compared to both sedentary groups, muscle fibre size was larger in the exercised ovariectomized animals. Our results indicate that ovariectomy-induced sarcopenia is not due to the loss of ovarian hormones per se, but is largely due to physical inactivity.

Lifelong sedentary behaviour and femur structure.

The aim of the present study was to analyze the lifelong differences of femur structure in sedentary and physically active animal models. Thirty male C57BL/6 mice, 2 months old, were either: i) housed in cages with running wheel (AA; n=10), ii) housed in cages without running wheel (AS; n=10), iii) or sacrificed without intervention (Y; n=10). AA and AS animals were sacrificed after 23 months of housing. Right femur structure was analyzed in all animals by histomorphometry. Significant differences in several microarchitectural parameters of cancellous and cortical bone were identified between Y mice and both groups of aged mice, as well as between AA and AS groups. Lifelong physically active mice had significantly higher cancellous bone surface (Cn.BS) and trabecular number (Tb.N) and decreased trabecular separation (Tb.Sp) at both epiphyses when compared to AS animals. No differences were observed between Y and AA groups regarding osteocyte number (N.Ot) despite its significant reduction in AS animals, suggesting that age alone was not a cause for decreases in N.Ot. Our results suggest that the reduced bone quality observed in the elderly is not only a consequence of age but also of lack of physical activity since sedentary behaviour significantly aggravated the degenerative age-related bone differences.