Affiliations: [a] Laboratory of Sport Biomechanics, Aristotle University
of Thessaloniki, Department of Physical Education and Sport Science, Serres,
Greece
Note: [] Address for correspondence: Vasilios I. Kalapotharakos, PhD,
Research Assistant, Aristotle University of Thessaloniki, Dept of Physical
Education and Sport Science, Agios Ioannis, Serres, Greece. Tel.: +30 2321 0
21618; E-mail: vasikal@yahoo.com
Abstract: The aim of the present study was to examine the effect of knee joint
angles on maximal voluntary contraction (MVC) of leg extensor and
electromyographic (EMG) activities of rectus femoris (RF), vastus medialis
(VM), and biceps femoris (BF) during a maximal isometric leg press task.
Eighteen males, aged 18–23, performed maximum bilateral voluntary isometric
contractions at five knee joint angles (90°,
80°, 70°, 60°, and 50°; 0°= full extension). The MVC of
leg extensors, the force exerted during the first 100~ms of the contraction
(F100), the time achieved the MVC, and the average integrated EMG activities
(AEMG) of RF, VM, and BF were measured at five knee joint angles. MVC was
significantly higher (p<0.05) at
60° in comparison to the other knee joint angles,
whereas AEMGs of RF and VM were significantly lower (p<0.05)
at more extended position (50° than at more flexed
positions (90°, 80°, and 70°). AEMG of BF did not present significant changes
among the five different knee joint angles. These findings suggest that MVC of
leg extensor are considerably influenced by the mechanical force-length
properties of skeletal muscle. The reduced activation of RF at more extended
knee positions indicates its multiple function along a closed chain multi-joint
task. On contrary, the similar activation of biceps femoris muscle at all five
knee joint angles indicates its importance for the knee joint stability.
