Influence of age on calf muscle length and passive stiffness variables at different stretch velocities

This study examined the influence of age on calf muscle length and passive stiffness variables at different stretch velocities. Ten younger aged men (31 [SD 6] years), nine middle aged men (48 [SD 6] years), and nine older aged men (70 [SD 6] years) were tested using a KIN-COM 500H dynamometer. The right calf muscles were stretched from relaxed plantar flexion to maximal passive dorsiflexion at four randomly ordered velocities of 5 degrees.s(-1), 30 degrees.s(-1), 60 degrees.s(-1) and 120 degrees.s(-1) with negligible surface EMG activity (< 0.05 mV) in the calf muscles at all velocities. The maximal passive dorsiflexion angle, maximal passive torque, initial passive angle (defined at 20% of the maximal passive torque), angular change, and passive stiffness ratios (Delta torque/Delta angle) through the defined range of motion (ROM) and through the last 10 degrees of ROM were analyzed with ANOVA procedures. The maximal passive dorsiflexion angle decreased as age increased (P < 0.05). The maximal passive torque increased as the velocity of stretch increased (P < 0.001) and velocity of stretch interacted significantly with the age groups (P < 0.01); the older men had less maximal passive torque at 60 degrees.s(-1) and 120 degrees.s(-1) (P < 0.05). The passive stiffness ratios through the defined ROM showed a significant effect of stretch velocity (P < 0.01). Within the last 10 degrees of dorsiflexion ROM the ratios showed a significant effect of group (P < 0.05), stretch velocity (P < 0.001), and interaction (P < 0.001). For the younger and middle aged men the passive stiffness increased as the stretch velocity increased, but for the older men the passive stiffness decreased as the stretch velocity increased, perhaps influenced by muscle atrophy, changes in muscle fiber type and changes in the amount of adipose tissue. The results indicated that decreased calf muscle length was associated with decreased maximal passive torque and decreased passive stiffness for older men beyond 60 years of age.