A biomechanical evaluation of cyclic and static stretch in human skeletal muscle

The short term effect of static and cyclic stretch paradigms on stiffness and maximal joint range of motion was examined in 12 recreational athletes. To assess flexibility, joint range of motion and resistance to stretch were measured using a dynamometer during a passive stretch of the hamstring muscle group to the point of pain. The recorded torque-angle curve allowed for identification of maximal joint range of motion and calculation of passive muscle-tendon stiffness and energy. Three flexibility assessments (stretch 1 - 3), each 10 min apart, were administered to each leg. A 90 s static stretch and 10 cyclic stretches were performed after the second stretch on the left and right side, respectively. Stiffness in a common range for stretch 1 - 3 was unchanged on both the left and right side. However, on the left side (static stretch) there was a significant effect of flexibility assessment (stretch 1 - 3) (p < 0.0001) with an increased maximal joint angle (p < 0.01) and maximal stiffness (p < 0.05) between all three stretches. Similarly, on the right side (cyclic stretches) there was a significant effect of flexibility assessment (p < 0.0001) with an increased maximal joint angle between stretch 1 and 3 (p < 0.01) and maximal stiffness (p < 0.05) between all stretches. During the static stretch passive torque declined 35+/-4% (p < 0.001). During the cyclic stretches passive energy and hysteresis both declined 17% (p < 0.05) while stiffness increased 12% (p < 0.05). The results of the present study demonstrate that static and cyclic stretching, as it is commonly performed by athletes, increases joint range of motion by increasing stretch tolerance while the viscoelastic characteristics of the muscle remain unaltered.