Effect of age on muscle activation and twitch properties during static and dynamic actions.

In this investigation we examined age-associated changes in peak torque, voluntary activation levels, and potentiated twitch properties of the knee extensors during isometric (ISO), shortening (SHO), and lengthening (LEN) actions in 18 young subjects (19-27 years) and 12 elderly subjects (64-77 years). Peak torque was lower for the elderly subjects under the ISO (-31%) and SHO (-28%) conditions (P < 0.05); however, the loss in LEN peak torque in the elderly was less marked (-17%) (P > 0.05). Voluntary activation levels within and between groups were not significantly different and ranged between 96.8% and 98.9% (P > 0.05). Peak twitch torque and some temporal twitch characteristics were altered with age (P < 0.05), but such changes were similar across all muscle actions (P > 0.05). These data suggest that the attenuated reduction in LEN muscle strength associated with age is probably not related to contraction-specific changes in voluntary activation levels or potentiated twitch properties. Muscle Nerve, 2009.