Affiliations: [a] Clinical Kinesiology Research Laboratory, School of
Physical Therapy and Rehabilitation Science, The University of Montana,
Missoula, MT 59812-4680, USA
Note: [] Address for correspondence: Richard L. Gajdosik, Professor and
Director, Clinical Kinesiology Laboratory, School of Physical Therapy and
Rehabilitation Science, The University of Montana, Missoula, MT 59812-4680,
USA. Tel.: +1 406 2434753; Fax: +1 406 2432795; E-mail:
richard.gajdosik@umontana.edu
Abstract: Studies have suggested that distance runners have decreased calf
muscle-tendon unit (MTU) flexibility, which is related to improved running
economy. This study examined the passive elastic properties of the calf MTU of
distance runners to test the hypothesis that they have increased passive
elastic properties measured in vivo. Ten distance runners (aged 18–21
years) and 10 untrained men (aged 23–28 years) were tested. A
Kin-Com® dynamometer stretched the right calf MTU
from plantarflexion (PF) to maximal dorsiflexion (DF) at
5°·s^{-1}(0.087
rad·s^{-1}) with minimal surface electromyogram
activity in the soleus, gastrocnemius, and tibialis anterior muscles. ANOVA
analyses indicated that the maximal DF ROM did not differ between groups, but
the maximal passive DF torque (Nm), total absorbed passive elastic energy (area
under full stretch curve [°·Nm]) and passive elastic stiffness
(Nm·°^{-1}) within the last 10° of the
stretch were greater for the distance runners when controlled for body mass
(P⩽0.007). The maximal passive DF torque and the passive elastic stiffness
were greater when controlled for PF maximal voluntary isometric contraction
torque (P⩽0.028). The increased passive resistive properties suggested
structural adaptations in the calf MTU, possibly the result of eccentric
loading and stretching, which would contribute to improved running economy.
Keywords: Distance runners, passive elastic properties, calf muscle-tendon unit
