Influence of an isometric fatiguing exercise on the length and
passive-elastic properties of the calf muscle-tendon unit of minimally active
young women
Affiliations: [a] The Clinical Kinesiology Research Laboratory, The
University of Montana, Missoula, MT, USA
Note: [] Address for correspondence: Michele H. Finlayson, The Clinical
Kinesiology Research Laboratory, School of Physical Therapy and Rehabilitation
Science, The University of Montana, Missoula, MT 59812-4680, USA. Tel.: +1 406
531 5514; Fax: +1 406 243 2795; E-mail:
michelehmf@hotmail.com/michelem@stanfordalumni.org
Abstract: 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.
