AMPLITUDE REDUCTION OF H-REFLEX DURING MENTAL MOVEMENT SIMULATION IN ELITE ATHLETES

In order to investigate the changes of motoneuron excitability during mental simulation of a voluntary movement (motor imagery; MI), the sol eus H-reflex and several activities of autonomic effecters were record ed simultaneously when MI of speed skate sprint was performed. The sub jects were seven elite speed skate athletes ranging in age from 18 to 24 years old. They were all skilled in MI, and could imagine full vivi d skating movement internally as if they were really exercising. The s ubjects were awake, relaxed and blindfolded. At first, rest (5 min), p ositive relaxation (4 min) and concentration periods (2.5 min) were se t up. Then, after the previous announcement for the start, MI was init iated by the sound of a signal gun which was recorded by a tape record er. MIs were continued for each subject from about 36 s to 38 s, and t hese imaging times were very close to the actual personal best records of each subject. The autonomic effecters represented by skin conducta nce response (SCR), heart rate (HR), and respiration rate (RSR) became remarkably active during MI in all trials. SCR was increased by 51% o n the average. Furthermore, HR and RSR were increased by 57% and 76% r espectively, compared with those during resting period. These changes in the autonomic effecters were all significant and were those which w ere activated in actual movements. The amplitudes of H-reflex were alm ost all constant before MI initiation. However, the reduction of the H -reflex amplitude arose just after the start and lasted to the end of MI. Relative values of the depressions were from 16% to 54% compared w ith those in rest period, and these depressions were significant stati stically (P<0.01) in all subjects and all trials. These results are di scussed from the point of view of motor program. It is suggested that some descending neural mechanism which reduces the motoneuron excitabi lity may be activated.