An Evaluation of the Length-Tension Relationship in Elderly Human Ankle Dorsiflexors

Abstract

Aging is thought to be associated with a decreased elasticity of skeletal muscle, which may be predicted to affect the optimal length at which peak tension is developed. This was assessed in the present study, in which we examined the effect of aging on the muscle length-tension relationship in the right ankle dorsiflexors of 60 subjects aged 20-40 years (M = 25.3; 15 males, 15 females) and 60-80 years (M = 68.8; 15 males, 15 females). Evoked contractile properties, 1-sec tetanic contractions (at 20, 50, and 80 Hz), and maximal voluntary contractions (MVC) were measured at 10 joint angles (15 degrees dorsiflexion to 30 degrees plantarflexion, in 5 degrees increments). Peak twitch torque occurred at the extreme of plantarflexion (30 degrees P) in both elderly and young adults, and although males had significantly greater twitch torques than females, there was no difference between the elderly and young adults. Maximum tetanic torque and MVC torque occurred at 30 degrees P and 20 degrees P, respectively, but in this case the young adults were significantly stronger than the elderly adults, and the males stronger than the females at all joint angles. There was no difference in the torque-angle relationship between elderly and young adults in any of the evoked or voluntary measures. At each of the three frequencies, the rise time of tetanic torque was also similar between elderly and young adults. These results suggest that any age-related change in the elastic properties of the ankle dorsiflexors does not affect the length (as inferred by joint angle)-tension relationship in this muscle group.