This study examined the effects of an isometric fatiguing exercise on selected length and passive-elastic properties of the calf muscle-tendon unit (MTU). The right calf MTU of 8 minimally active women 22–34 years of age were stretched by a Kin-Com® dynamometer motor from plantarflexion to a constant maximal dorsiflexion (DF) angle at 5°ċ s
$^{-1}$
to measure angular and resistive torque differences before and immediately after an isometric fatiguing exercise. Minimal surface electromyogram (EMG) activity from the soleus, gastrocnemius and tibialis anterior muscles ensured the stretches were passive. The muscles were fatigued by 60 s isometric plantarflexion trials at 80% of the maximal voluntary contraction (MVC) force with 15 s rests between trials until the force fell below 50% MVC, which was associated with increased EMG activity of the plantarflexors. One-way ANOVAs showed that the initial passive DF angle and therefore the length extensibility did not change. The maximal and mean passive DF torque and the area under the curve also did not change, but the full stretch average passive-elastic stiffness increased (P=0.005). The results suggested that the length and passive resistive properties of the calf MTU are maintained and the average passive-elastic stiffness is increased after an active isometric fatiguing exercise.
