The effects of dynamic stretching on the passive properties of the muscle-tendon unit

The purpose of this study was to examine the effects of dynamic stretching on the passive biomechanical properties and isometric muscle strength of the knee flexors. Fourteen healthy men (mean +/- s: age=24 +/- 3 years) performed passive range of motion assessments and isometric maximal voluntary contractions of the knee flexors at knee joint angles of 35 degrees, 50 degrees, 65 degrees, 80 degrees, and 95 degrees below full knee extension before and after dynamic stretching. In addition, electromyographic amplitude was recorded from the biceps femoris during the maximal voluntary contractions. Passive stiffness and passive resistive torque were measured during pre- and post-dynamic stretching. The dynamic stretching included the participant extending their right leg outwards to the end range motion and pulling their leg back towards the body while seated in the isokinetic dynamometer for four 30-s bouts with 20-s rest between bouts. Passive range of motion increased while passive stiffness and passive resistive torque decreased following dynamic stretching. Peak torque decreased at knee joint angles of 65 degrees and 80 degrees below full extension, while electromyographic amplitude decreased following dynamic stretching. Dynamic stretching resulted in changes to passive stiffness and passive resistive torque that are typically reported following static stretching, however, there were decreases in peak torque at two of the knee joint angles.