Early-onset calorie restriction conserves fiber number in aging rat skeletal muscle.

The purpose of this work was to determine the effect of early-onset calorie restriction on sarcopenia in the aging rat. Ad libitum (AL) fed animals were examined at 5, 18, 21, and 36 months of age. Calorie-restricted (CR) rats, 40% restricted since 4 months of age, were examined at 21 and 36 months of age. By 36 months, vastus lateralis, rectus femoris and soleus muscles, from AL-fed rats, had significant muscle mass and fiber loss, and reduced muscle cross-sectional area. Mean fiber diameter decreased with age in the vastus lateralis and rectus femoris but not the soleus of AL-fed rats. The number of Type I fibers significantly increased in the vastus lateralis with age. Calorie restriction did not prevent muscle mass loss with age; however, it significantly reduced muscle mass loss between 21 and 36 months of age compared with age-matched AL cohorts. Calorie restriction prevented fiber loss with age, and this conservation of fiber number reduced muscle mass loss with age.