Stretch reflex responses following mechanical stimulation in power- and endurance-trained athletes.

The basic stretch reflex responses evoked by the mechanical stimuli were investigated among different athletic groups. The tests were performed by a special ankle ergometer, which created dorsiflexion velocities from 25 deg x s-1 to 115 deg x s-1 around the ankle joint. The EMG activity of soleus (SO), gastrocnemius (GA) and tibialis anterior (TA) muscles was recorded with surface electrodes. In all subjects higher angular velocities caused higher stretch reflex responses. The endurance-trained athletes were more sensitive to the used stimuli than the power-trained athletes, because of their shorter latency times (43 +/- 7 ms vs 45 +/- 7 ms, p < 0.001 for the SO muscle and 40 +/- 8 ms vs 43 +/- 6 ms, p < 0.001 for the GA muscle), longer duration of action potentials and shorter recovery times of the monosynaptic reflex. Thus, the neural control of reflex movements in skeletal muscles was dependent on the training background of the subjects. Additionally, the findings may be explained by differences in the motor unit composition as well as by possible differences in the muscle spindle density of the two subject groups.