Dependence of reaction times on movement patterns: effects of forehand and backhand stroke practice by the preferred hand

Abstract

In normal subjects, the premoter time and electromyographic reaction time (EMG-RT) of the biceps brachii has been determined to be different in flexion (F) and supination (S) of the forearms. Accordingly, while the same muscle performs in both functions, these two voluntary movements would be sepatately organized in the brain. Moreover, the EMG-RT differences, obtained by subtracting the EMG-RTs of S from those of F, disappeared in athletes of unilateral sporting events'(Kasai, 1982; l983). The present experiments are therefore undertaken to examine the effects of forehand and backhand stroke practice by the preferred hand on the EMG-RTs of F and S, and to collect information with respect to the practice influences on the motor control systems in the brain. Subjects for forehand stroke practice were 36 normal subjects (24 males and 12 females) in the practice group and 27 normal subjects (13 males and 14 females) in the non-practice group, and 21 normal male subjects for backhand stroke practice, respectively. They were all right-handed and by self report did not have considerable amount of experience in unilateral sporting events. The tasks of the subjects were the F and S of both arms simultaneously, responding to a sound signal as quickly as possible. EMG-RTs were measured with the surface EMG of the biceps brachii. The EMG-RTs of F and S were measured six times per each subject. Session 1 was administered to assess the pre-practice (P) EMG-RT. Subsequently, one session was designated to be 100 forehand and backhand strokes practiced by the preferred hand. Five sessions were repeated. A 5-min. rest period was allowed for recovery following each practice session to prevent any cumulative fatigue effect. At the end of each practice session, the EMG-RTs of F and S were measured, respectively. For the purpose of analysis of practice after-effect, the EMG-RTs of F and S of the same subjects in the forehand practice group were measured 3-4 months after the initial sessions. Overall, the EMG-RTs of F and S were measured 7 times per each subject in the forehand practice group. In the non-practice group, the 6 sessions of EMG-RT measurement were performed using the same procedure employed for the practice group without the practice tasks. In the backhand stroke practice group, experimental procedures for the measurement of EMG-RTs and practice were same as those of the forehand stroke practice group without the after-effect examination. The main findings in the present study are summarized as follows: 1. The EMG-RTs of F and S did not change in the forehand stroke practice of the preferred hand. 2. The EMG-RT differences of the practiced hand (right hand) changed significantly. 3. In the non-practice group, the EMG-RT differences of both sides did not change. This result indicates that changes in EMG-RT differences in the practice group resulted from forehand stroke practices by the preferred hand. 4. However, those changes disappeared in 3-4 months after practices. 5. In the backhand stroke practice group, the EMG-RTs of F and S did not significantly change, similar to the findings of the forehand stroke practice group, but the EMG-RT differences of both sides varied significantly in preferred hand practice. 6. Electromyographic discharge patterns of upper-limb muscles between forehand and backhand stroke were definitely different. The findings are interpreted as follows: First, the motor pattern generator would be influenced by unilateral forehand and backhand stroke practices. Moreover, the difference of the practice task (movement pattern) plays an important role in different functional changes of the motor pattern generator: Second; the period of continuation of the practice plays an important role in changes of the quality of a system programming the movement patterns (the motor control systems). From these interpretations, it is suggested that the quality of movement

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