Coactivation of the flexor muscles as a synergist with the extensors during ballistic finger extension movement in trained kendo and karate athletes

To analyse the effects of ballistic property training on ballistic finger e xtension movement, surface electromyographic pattern (EMGs) of the finger e xtensor and flexor muscles and the acceleration signal of the middle finger were recorded in trained kendo and karate athletes, and sedentary non-athl etic men. Ballistic finger extension did not show the characteristic tripha sic EMC pattern reported in single joint, but a coactivation of flexor and extensor muscles, Reaction time (RT) in kendo (143 +/- 12 msec) and karate (146 +/- 11 msec) athletes were significantly shorter than that in the cont rol (176 +/- 12 msec). The shortenings of the RT were attributed to both th e shortenings of premotor time and motor time, The delay of the flexor musc les discharge after those of the extensors in kendo (0.8 +/- 7.0 msec) and karate (- 0.2 +/- 5.0 msec) athletes was significantly shorter than in cont rol (12.7 +/- 5.6 msec), These results suggest that the RT is shortened thr ough motor learning in the kendo and karate athletes who trained for moment ary movements; and that the flexor muscles may play an important role as a synergist in heightening the efficiency of ballistic finger extension in co ordination with the extensor muscles.