Dependence of Muscle Torque of Ankle Plantar and Dorsal Flexors on Different Ankle Angles

Abstract

Research background and hypothesis. There is much research information about the relationship between
the knee joint angle and the quadriceps muscle torque (Mohamed et al., 2002), but still we lack evidence about
the relationship between ankle angle and calf muscle torque.
Research aim. The purpose of this research was to establish the dependence of maximal voluntary contraction
(MVC) and electrical stimulation (ES)-evoked torque and calf muscle electrical activity (EMG) on different ankle
plantar and dorsal fl exion angles. We hypothesized that the calf muscle MVC and ES-evoked torque as well as
muscle EMG amplitude would increase with increasing muscle length (i. . increasing ankle angle).
Research methods. The subjects in the research were ten non-trained men. Calf plantar and dorsal fl exors
muscle ES and MVC torque were tested at eight different ankle angles (–25 o ; –15 o ; –5 o ; 0 o ; 15 o ; 25 o ; 35 o ; 45 o )
which were chosen in randomized sequence. The tibialis anterior, soleus, gastrocnemius lateralis and medialis
muscle EMG were measured during muscle MVC.
Research results. The results showed that the highest ES-evoked and MVC developed torque of plantar
fl exion muscles was at –25° ankle angle (149.1 ± 31.6 N·m and 207.8 ± 38.1 N·m, respectively), while the highest
dorsal fl exion MVC muscle torque was at 25° ankle angle (47.2 ± 8.1 N·m). However, dorsal fl exion muscle MVC
torque increased with the muscle length only until 25° ankle angle.
Discussion and conclusions. Plantar flexion muscle electrical stimulation evoked and plantar / dorsal
fl exion muscle maximal voluntary contraction torques are highest at that ankle angle where muscle length is the
longest.

Keywords: maximal voluntary contraction, electrical stimulation, EMG.