Normalized lengthening peak torque is associated with temporal twitch characteristics in elderly women but not young women

Abstract

To determine if greater normalized torque during maximal effort lengthening actions in elderly women compared with young women is related to age-associated adjustments in neural activation and/or contractile function. The right knee extensors of 14 young women (21-30 years) and 12 elderly women (65-78 years) were assessed for isometric, shortening and lengthening peak torque, electromyography (EMG) activity, and isometric twitch contractile properties. Knee extensor contractile tissue volume was determined using magnetic resonance imaging. Normalized torque was determined as peak torque per unit of knee extensor contractile tissue volume. Normalized torque during the isometric and shortening actions was similar between age groups (P > 0.05); however, lengthening normalized torque was significantly higher for the elderly women (P < 0.05). In the young women, a significant relationship existed between normalized torque and EMG for all muscle actions (P < 0.05), while no association was found between normalized torque and temporal twitch characteristics for any muscle action (P > 0.05). In the elderly women, a significant relationship existed between normalized torque and EMG for the isometric and shortening muscle actions (P < 0.05), but not for lengthening normalized torque and EMG (P > 0.05). Furthermore, no association existed between isometric and shortening normalized torque, and temporal twitch characteristics in the elderly women (P > 0.05); however, a significant relationship existed between lengthening normalized torque, and the rate of relaxation and contraction duration (P < 0.05). The greater capacity to develop lengthening peak torque relative to contractile tissue volume in the elderly women appeared to be associated with age-related adjustments in the temporal twitch characteristics rather than neural activation.