DISCUSSION
Confirming previous reports, this study demonstrates that isometric muscle strength and muscle power decline considerably with aging. Furthermore, we showed that, independent of age and in both genders, low muscle strength and power are strongly associated with two complementary definitions of poor mobility. On the contrary, calf muscle cross-sectional area, an indicator of muscle mass, shows only a moderate decline with aging, and a small calf muscle cross-sectional area is a weak and inconsistent predictor of mobility limitations.Similar to other authors (3), we found that the percent per year drop in muscle power is substantially larger than the per year drop in isometric strength. Based on this observation, the same authors recommended that muscle power be the method of choice for the early detection of patients with sarcopenia. Indeed, in our study population, the estimated prevalence of sarcopenia based on “low muscle power T-score” was much higher than the prevalence estimated by using definitions based on isometric strength and calf muscle cross-sectional area. However, many persons with a low muscle power T-score showed no evidence of mobility limitations. In fact, in a ROC analysis, knee-extension torque, handgrip, and lower extremity muscle power showed similar good discriminating value in the identification of poor mobility, defined either as walking speed