The decline in muscle function is associated with age-related decrease in muscle mass and age-related decline in strength. However, decreased strength is not solely due to decreased muscle mass. Age-related decline in muscle specific force (force/muscle cross-sectional area), a measure of intrinsic muscle function, also contributes to age-related strength decline and the mechanisms by which this occurs are only partially known. Moreover, changes in the extracellular space could have a profound effect on skeletal muscle function. Life-long calorie restriction (CR) in rodents has shown to be a powerful anti-aging intervention. We examined whether CR is able to attenuate the loss of muscle function and elevations in extracellular space associated with aging. We hypothesize that CR attenuates the age-associated decline in specific force and increases in extracellular space. Measurements of in vitro contractile properties of the extensor digitorum longus (Type II) and soleus (Type I) muscles from 12-month and 26-28-month old ad libitum fed, as well as 27-28-month old life-long calorie restricted male Fischer-344 rats were performed. We found that calorie restriction attenuated the age-associated decline in muscle mass-to-body mass ratio (mg/g) and strength-to-body mass ratio (N/kg) in the extensor digitorum longus muscle (p<0.05), but not the soleus muscle (p>0.05). Importantly, muscle specific force (N/cm²) in the extensor digitorum longus, but not the soleus muscle of the old calorie restricted rats was equal to that of the young 12-month old animals. Moreover, the age associated increase in extracellular space was reduced in the fast extensor digitorum longus muscle (p < 0.05), but not in the soleus muscle with calorie restriction. We also found a significant correlation between the extracellular space and the muscle specific force in the extensor digitorum longus (r = -0.58; p<0.05), but not in the soleus muscle (r = -0.38; p>0.05). Hence, this study shows a loss of muscle function with age, and suggests that long-term calorie restriction is an effective intervention against the loss of muscle function with age.