Biomechanical behavior of the plantar flexor muscle-tendon unit after an Achilles tendon rupture

The purpose of this study was to examine the biomechanical behavior of the plantar flexor muscle-tendon unit in subjects who had ruptured their Achill es tendon. Twenty-six men and 14 women volunteered for the study, Eighteen subjects had been treated operatively and 22, nonoperatively. All subjects had ruptured their Achilles tendon more than 1 year before the study, and 2 8 of the 40 ruptures occurred 5 years or less before the day of testing. A KinCom dynamometer was used to measure ankle joint angle, passive torque, a nd maximal isometric plantar flexor torque. During a 2-minute passive calf stretch, stiffness and torque relaxation were calculated. Isometric torque and peak passive torque were 17% and 10% greater for the uninvolved versus the involved limb, whereas stiffness and torque relaxation were not differe nt between limbs. The time since injury did not influence the results, nor did the mode of initial treatment, that is, whether the subjects were treat ed operatively or nonoperatively. These findings suggest that changes in st rength and peak passive torque may be chronic adaptations associated with A chilles tendon rupture.