POTENTIATION OF CONCENTRIC PLANTAR FLEXION TORQUE FOLLOWING ECCENTRICAND ISOMETRIC MUSCLE ACTIONS

In a stretch-shortening cycle (SSC) the concentric muscle action is en hanced by a preceding eccentric muscle action. The hypothesis of the p resent study is that a preceding isometric action can also have an eff ect on a following concentric action, but to a lesser degree. A KINeti c-COMmunicator II dynamometer was used to test muscle strength of the plantar flexion of the right foot in 20 healthy women. Maximal volunta ry torque measurements were made at different angular velocities (120 degrees s(-1) and 240 degrees s(-1)) and the range of motion of the an kle joint was 78-125 degrees. The assessment was based on concentric t orque output and EMG recording from the gastrocnemius muscle under thr ee different types of testing conditions (concentric actions with and without preceding eccentric or isometric actions, all with maximal eff orts). The results showed that preceding muscle actions led to greater concentric torque output (P < 0.01) between 80 and 99 degrees plantar flexion. However, the increase in the concentric action was significa ntly (P < 0.01) larger with eccentric than with isometric preceding ac tion, regardless of velocity. The EMG activity of the concentric actio n showed unchanged or lower values when preceded by a muscle action. I n this model our conclusion is that the main reason for larger concent ric torque values after a preceding muscle action is that time is suff icient for maximal muscle tension development; in addition, elastic en ergy is stored, particularly during the preceding eccentric action. Ou r results show that the effect of preceding muscle actions should be t aken into account when measuring isokinetic muscle strength at relativ ely small angular movements.