Dynamic elastic and static viscoelastic stress-relaxation properties of the calf muscle-tendon unit of men and women

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((R)) dynamometer moved the ankle of 15 men and 14 women (age range 23-35 years) from plantarflexion to maximal dorsiflexion (DF) at 5 degrees/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 degrees 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.