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Changes in connective tissues of the skeletal muscle-tendon unit (MTU) of aging animal muscles have been associated with increased passive viscoelastic properties. This study examined whether similar changes in the viscoelastic properties were present in short calf MTUs of older women in vivo. Fifteen women 68-87 years of age with short calf MTUs, as represented by limited active dorsiflexion (DF) range of motion (ROM) of < or =5 degrees, and 15 women 20-26 years of age without decreased DF ROM participated. A Kin-Com dynamometer stretched the MTU from plantarflexion to maximal DF at the slow velocity of 5 degrees s(-1) (0.087 rad s(-1)) and the fast velocity of 120 degrees s(-1) (2.094 rad s(-1)) with minimal surface electromyogram activity in the soleus, gastrocnemius, and tibialis anterior muscles. Two-way analysis of variance (ANOVA) tests for repeated measures (Velocity x Group) indicated that all women showed greater passive torque, average passive elastic stiffness, and total absorbed passive elastic energy for the fast stretch than for the slow stretch (P < 0.001). The older women had greater percent increases for the average passive torque (30%) and total absorbed passive elastic energy (26%) for the fast stretch than the younger women (P < 0.05), who had 17.5 and 13% increases, respectively. The older women had less maximal and average passive torque (Nm) and total absorbed passive elastic energy (degrees Nm), but greater average passive elastic stiffness (Nm degrees (-1)) at both stretch velocities (P < 0.001). The results indicated that short calf MTUs of older women have increased passive viscoelastic properties that could have implications for balance and ambulatory function.

Examine the slow passive stretch and release characteristics of the calf muscles of older women with limited dorsiflexion range of motion.A cross-sectional comparative design.The passive stretch and release characteristics of the calf muscles of older women with limited dorsiflexion range of motion have not been studied.Fifteen older women (mean 79 years) with active dorsiflexionor =10 degrees and 15 younger women (mean 24 years) without limited dorsiflexion were tested. The right ankle was stretched from plantarflexion to maximal dorsiflexion and released into plantarflexion at 5 degrees /s with minimal surface EMG activity in the soleus, gastrocnemius, and tibialis anterior muscles. Length, passive-elastic stiffness and stored passive-elastic energy were examined.The older women had less maximal passive dorsiflexion, a greater initial stretch angle, and less angular change than the younger women (P0.05). The maximal passive resistive force (Newtons) of the stretch phase, and the stored passive-elastic energy ( degrees N) during both stretch and release phases were also less (P0.001). The older women had greater passive-elastic stiffness at 0 degrees and 5 degrees of dorsiflexion (P0.001).The older women had decreased calf muscle length, extensibility, maximal passive resistive force, stored passive-elastic energy, but greater angle-specific-stiffness at 0 and 5 degrees of passive dorsiflexion.Older women with limited dorsiflexion range of motion have decreased calf muscle length, passive resistive forces and stored passive-elastic energy that may impact static and dynamic standing balance activities. Greater passive-elastic stiffness within their ambulatory dorsiflexion range of motion may partially compensate for the deficits.