CINEMATIC ANALYSIS OF THE ANKLE AND SUBTALAR JOINTS RELATED TO MYOELECTMC ACTIVATION PATTERNS IN JUMPING EXERCISES UNDER INCREASE STRETCHING LOADS

Abstract

The study of the Rear foot mobility around the subtalar joint during running and jumping exercises, has been done since 1978. In epidemiological studies the amount of eversion (pronation) is often related to injuries on the mediolateral muscles an also to Tibialis and Achilles tendons injuries. Same experiments have been made to study the rearfoot mobility considering the action of muscles located around the subtalar and ankle joints. Stacoff et al. (1988) used one mechanical model that included mediolateral muscles, the maximal force of each muscles was considered to be function of is cross sectional area. Studies that integrate both, the cinematic analysis of the rearfoot mobility around the subtalar joint and the determination of EMG activation patterns of the muscles acting on the subtalar joints are uncommon. The purpose of this work is to study the EMG patterns of same of the leg muscles involved in ankle and subtalar movements, during action against the ground, in jumping exercises under increase stretching load, looking for possible relations with the cinematic analysis of subtalar movement during ground contact phase. Five adult elite sprinters performed drop jumps under three load conditions 40cm, 50cm and 70cm. On condition five trials were recorded allowing the use of average techniques. The signals from Force Plate, Knee and Ankle electrogoniometers, and surface EMG, were A/D converted at IOOOHz (Biopac-MP100). The EMGs of Gastrocnemius (GN), Soleus (SOL), Tibialis A. (TA) and Peronis L. (PL) were filtered, fullwave rectified and smoothed. The subjects foot and leg were filmed from behind at 50 framesls. The EMG patterns of extensor muscles under SSC conditions have three functional phases, Preactivation (before touchdown (TD), Reflexive Potenciation 30-100 ms after TD and Voluntary Activation, iEMGs of this phases were calculated. PL SOL and GN act almost simultaneously during ground contact, the a higher preactivation on the GN, could be explained by the higher rate of FastT. fibbers, greater crossectional area and is superficial position. The high level of preactivation on TA appears to be related with anticipation of the forced eversion occurring after touchdown, notice that TA works as extension antagonist. This amount of activation of TA on Touchdown could explain same of the stress related TA tendon injuries.