Acute effect of repeated maximal isometric contraction on electromechanical delay of knee extensor muscle

The purpose of this study was to investigate the effect of repeated maximal isometric contraction on electromechanical delay (EMD) of the quadriceps femoris muscle. Eleven college-aged subjects participated in an exercise protocol which consisted of 25 one-leg maximal knee extensions each lasting 8 s, followed by a 2-s relaxation. Surface electromyography (EMG) was recorded from the vastus lateralis and rectus femoris muscles, and contraction force was recorded using a load cell which was strapped to the lower leg. The peak contraction force, peak rate of force development, muscle fibre conduction velocity and EMD in maximal voluntary contraction (MVC), electrically stimulated and patellar tendon reflex contractions were measured before and after the exercise. The results showed a significant elongation in EMD, from 37.8 (SEM 1.0) ms at rest to 56.5 (SEM 3.2) ms at the end of exercise, as well as impaired contractile performance in MVC. The EMD of the electrically stimulated and reflex contractions were also significantly increased after exercise, but to a lesser magnitude compared with MVC. The elongation of EMD required about 10 min to recover after exercise. This finding could be useful when evaluating the effect of strenuous exercise on the electro-mechanical responses of the muscle in subsequent exercise.