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The purpose of this study was to compare the dynamic elastic and static viscoelastic stress-relaxation (VSR) properties of the calf muscle-tendon unit (MTU) between men and women. A Kin-Com® dynamometer moved the ankle of 15 men and 14 women (age range 23-35 years) from plantarflexion to maximal dorsiflexion (DF) at 5°/s with negligible surface electromyogram activity to measure the dynamic passive elastic properties. The ankle was then moved to three DF angles defined at 100%, 90% and 80% of the maximal DF force and held for 60 s each to measure the static VSR as the torque decline. ANOVA procedures indicated that the men had greater absolute dynamic maximal passive DF torque, full stretch mean torque, absorbed passive elastic energy (area under the curve) and passive elastic stiffness through the full stretch and through the last 10° of the stretch (P ≤ 0.014). All but the full stretch stiffness remained significantly greater when controlled for body mass (P ≤ 0.042). The absolute torque decline for the three static stretches showed significant group, time and interaction effects (P < 0.001). The percent torque decline during the first 15 s of static stretch, normalized to the total percent decline (100%), was greater for men at the 90% (P = 0.049) and 80% (P = 0.036) stretch angles. The results indicated that the calf MTU of men has greater dynamic elastic and static VSR properties than women, which may influence ambulatory functional activities and adaptations to therapeutic stretching.

Calf muscle stretching programs are used to increase dorsiflexion range of motion at the ankle, yet the effects of the stretching programs on the passive properties of aged calf muscles and on standing and ambulatory function have not been studied. This initial study examined the effects of an eight-week stretching program on the passive-elastic properties of the calf muscles of older women and on selected functional activities.Nineteen women aged 65-89 years with limited dorsiflexion range of motion first completed a timed agility course, a timed 10-m walk and a standing functional reach test. A dynamometer then moved the right ankle from plantarflexion to maximal dorsiflexion and back to plantarflexion at 5 deg s(-1) to measure calf muscle passive properties. The women were randomly assigned to a group that stretched three-times a week for eight-weeks (n=10) or to a control group (n=9) that did not. The tests were repeated after the stretching program.The stretching group showed increased maximal dorsiflexion range of motion, passive resistive forces (Newtons [N]), and the absorbed and retained passive-elastic energy (deg N) (P0.05). They also had decreased times for the agility course and the 10-m walk (P0.05). The functional reach test did not change for either group.The eight-week stretching program most likely increased the maximal length, length extensibility and passive resistive forces of the calf muscles. Adaptations of other ankle and leg structures also may have contributed. The passive adaptations were associated with enhanced performances of ambulatory functional activities.

Studies have suggested that distance runners have decreased calf muscle-tendon unit (MTU) flexibility, which is related to improved running economy. This study examined the passive elastic properties of the calf MTU of distance runners to test the hypothesis that they have increased passive elastic properties measured in viva. Ten distance runners (aged 18-21 years) and 10 untrained men (aged 23-28 years) were tested. A Kin-Corn® dynamometer stretched the right calf MTU from plantarflexion (PF) to maximal dorsiflexion (DF) at 5°.s -1 (0.087 rad.s -1 ) with minimal surface electromyogram activity in the soleus, gastrocnemius, and tibialis anterior muscles. ANOVA analyses indicated that the maximal DF ROM did not differ between groups, but the maximal passive DF torque (Nm), total absorbed passive elastic energy (area under full stretch curve [°.Nm]) and passive elastic stiffness (Nm.° -1 ) within the last 10° of the stretch were greater for the distance runners when controlled for body mass (P ≤ 0.007). The maximal passive DF torque and the passive elastic stiffness were greater when controlled for PF maximal voluntary isometric contraction torque (P < 0.028). The increased passive resistive properties suggested structural adaptations in the calf MTU, possibly the result of eccentric loading and stretching, which would contribute to improved running economy.

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.