Weakness, SR function and stress in gastrocnemius muscles of aged male rats.

Aging is associated with a decline in muscle force that exceeds loss of muscle mass, suggesting that factors other than sarcopenia affect age-related muscle weakness. Here, we investigate in situ muscle force and sarcoplasmic reticulum (SR) properties in gastrocnemius muscles of adult (6-8 months) and aged (24 months) rats. Despite minimal loss of muscle mass, peak tetanic force was significantly reduced (-28%) in aged muscles.