Soleus and EDL muscle contractility across the lifespan of female C57BL/6 mice.

All previous aging research on the contractility of rodent skeletal muscle has been conducted on male rodents. Because males and females age differently, we undertook this study to determine if and when age-related decrements in skeletal muscle contractility occur in female mice. Soleus and extensor digitorum longus (EDL) muscles from female C57BL/6 mice aged approximately 4, 8, 16, 24 and 28 mo were assessed in vitro for contractility and subsequently contractile protein content. EDL muscle was resistant to age-related changes in force generation but displayed characteristics of becoming more slow-twitch like. Maximal isometric tetanic force (Po) generated by soleus muscle declined with age. Soleus muscle size and contractile protein contents were not affected by age and thus could not explain the age-related force decrements. Soleus muscle specific Po declined with age being approximately 26% lower in muscles of 16-28 mo-old mice indicating that a deterioration in soleus muscle quality of female mice occurred beginning around the age of ovarian failure. Thus this study provides essential, comprehensive baseline data for future studies on age-related muscle dysfunction in the female mouse.