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 extension movement, surface electromyographic pattern (EMGs) of the finger extensor and flexor muscles and the acceleration signal of the middle finger were recorded in trained kendo and karate athletes, and sedentary non-athletic men. Ballistic finger extension did not show the characteristic triphasic EMG 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 control (176 +/- 12 msec). The shortenings of the RT were attributed to both the shortenings of premotor time and motor time. The delay of the flexor muscles 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 control (12.7 +/-5.6 msec). These results suggest that the RT is shortened through motor learning in the kendo and karate athletes who trained for momentary movements; and that the flexor muscles may play an important role as a synergist in heightening the efficiency of ballistic finger extension in coordination with the extensor muscles.