CONTRACTION SPECIFIC CHANGES IN PASSIVE TORQUE IN HUMAN SKELETAL-MUSCLE

The present investigation examined passive torque and electromyographi c response in human skeletal muscle during passive static stretch with in 60 s after maximal repetitive eccentric and concentric contractions . Passive torque (Nm) offered by the hamstring muscle group was measur ed during passive knee extension in a modified dynamometer in 10 subje cts. The distal thigh was elevated to 0.52 rad from horizontal and the backrest was positioned at 1.57 rad. The lever arm moved the leg pass ively at 0.09 rad s(-1) from a starting position of 1.48 rad below hor izontal to the final position where it remained stationary for 90 s. G ross electrical activity of the human hamstring muscle group was recor ded simultaneously. The effect of concentric or eccentric contraction was tested on separate days. Two stretch manoeuvres with a 45 min hiat us were administered on a control and experimental side. The experimen tal side performed 40 maximal effort repetitive concentric or eccentri c hamstring muscle contractions at 1.05 rad s(-1) prior to the second stretch. Passive torque during the 90 s stretch declined 30-35% on the experimental and control side in all stretches, P < 0.001, without a significant effect of prior contraction mode. Passive peak and final t orques were lower on the experimental side, P < 0.01 after concentric contractions. Passive peak and final torques remained unchanged after eccentric contractions on the experimental side. The low level EMG res ponse of the hamstring muscle during the stretch was unchanged after m aximal repetitive concentric or eccentric contractions. These data dem onstrate acute contraction specific alteration in passive torque in hu man skeletal muscle, which cannot be accounted for by EMG activity. Fu rthermore, the lack of difference on the control side implies that one 90 s stretch has no effect on passive torque of the muscle 45 min lat er.