Influence of Age on Length and Passive Elastic Stiffness Characteristics of the Calf Muscle-Tendon Unit of Women

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Abstract
Background and Purpose. Therapeutic stretching of the calf muscle-tendon unit is used to increase its length and to ameliorate decreased dorsiflexion range of motion (ROM), but the influence of age on the passive properties of the calf muscle-tendon unit has not been studied adequately. The purpose of this study was to examine the influence of age on length and passive elastic stiffness (PES) characteristics of the calf muscle-tendon unit when stretched through the full, available dorsiflexion ROM. Subjects. Twenty-four younger women (aged 20–39 years), 24 middle-aged women (aged 40–59 years), and 33 older women (aged 60–84 years) participated. Methods. An isokinetic dynamometer was used to passively stretch the right calf muscle-tendon unit from relaxed plantar flexion to the maximal angle of available dorsiflexion at 5°·s−1. The maximal passive resistive torque was measured, and passive angle-torque curves were constructed for a full ROM from an initial angle of passive resistive torque to the maximal dorsiflexion angle. The full ROM represented length extensibility. The average PES was calculated for this full stretch ROM and for the first half and the last half of this stretch ROM. The maximal passive dorsiflexion angle, maximal passive resistive torque, angular change for the full stretch ROM, and average PES for the full stretch ROM and the first half and the last half of the full stretch ROM were examined for group differences and their relationships with age. Results. The maximal passive dorsiflexion angle, maximal passive resistive torque, angular change for the full stretch ROM, and average PES within the last half of the full stretch ROM were less for the older women than for the younger women. Age was negatively associated with these variables. Conclusion and Discussion. Decreased maximal passive dorsiflexion ROM in older women was associated with decreased maximal passive resistive torque, decreased calf muscle-tendon unit length extensibility, and decreased average PES within the last half of their available passive dorsiflexion ROM.