EFFECT OF PRIOR ISOMETRIC MUSCLE ACTION ON CONCENTRIC TORQUE OUTPUT DURING PLANTAR FLEXION

The influence of different levels of prior isometric muscle action on the concentric torque output during plantar flexion was examined at tw o angular velocities (60 degrees . s(-1) and 120 degrees . s(-1)) in t en healthy female subjects. The levels of the prior muscle actions wer e 25%, 50%, 75% and 100% of the maximal voluntary isometric contractio n (MVIC). A KINetic-COMmunicator II dynamometer was used to measure to rque output during plantar flexion within a range of motion of 78 degr ees-120 degrees of the ankle joint. Simultaneous recordings of electro myograms (low-pass filtered and rectified) were obtained from the gast rocnemius medialis muscle and the soleus muscle. Torque-angle curves w ere made for the plantar flexions using different prior muscle actions . Up to 75% of MVIC, the torque output in the first part of the range of motion increased with the level of the prior isometric muscle actio n; at higher levels of MVIC the torque did not appear to increase any further. Later in the range of motion, after 24 degrees in the plantar flexion at a velocity of 60 degrees . s(-1) and 31 degrees at 120 deg rees . s(-1), the prior muscle actions had no further influence. No in crease was found in the electromyograms, with one exception, during th e concentric movements when preceded by higher levels of MVIC. It woul d seem therefore that the increase in torque output early in the range of motion cannot be explained on the basis of differences in electric al muscle activation in this study.