Dependence of reaction times on movement patterns: develop-mental changes and sexual differences

Abstract

As children age , motor performance improves . There are many variables discussed in the development literature to which these changes in performance are attributed. Those mentined most frequently are physical growth, biomechanical and physiological factors. Overviews of these factors have been presented elsewhere (cf. Thomas. 1980). Reaction time experiments have often been used to investigate developmental variables affecting the motor output Process (Furui, Seki and Kasai, 1983). In normal subjects, the premotor reaction time (PMT) of the biceps brachii has been determined to be different in flexion (F) and supination (S)of the forearms. Accordingly, because the same muscles performs in both functions and PMTs of those two different movement patterns are definitely different, this would suggest that these two voluntary movements would be separately organized in the brain (Kasai, 1983, 1984). The present experiments are therefore undertaken to examine the developmental changes and sexual differences of these motor output systems by means of those reaction time tasks and collect information with respect to which these changes in performance are attributed. The subjects for the present study are 100 male children (20 subjects from seven to eleven years old, respectively) and 98 female children (20 subjects in each age category, except nine-years old). They were all right-handed. The tasks of the subject were the F and the S of right forearm only, responding to a sound signal as quickly as possible. Mechanical reaction timed (MRTs) of the F and the S were measured with the digitimer. The premotor reaction times (PMTs) of both movement patterns with the surface EMG of the biceps brachii among the nine, ten and eleven years old groups, respectively were also measured. As the regression coefficience of MRT and PMT in the F and the S were extremely significant (Furui, Seki and Kasai, 1983), motor times (MTs) were obtained by subtracting PMTs from MRTs. The main findings in the present study are summarized as follows: 1. MRTs of mrile and female children shortened in both movement patterns as they grew older. Those phenomena were especially noticeable between seven and nine years old. 2. MRTs of the F were always shorter than those of the S. However, MRT differences between two movement patterns disappeared at eleven years old. 3. MRTs of male children in both movement patterns were always shorter than those of female children. Since PMTs of male and female children in both movement patterns were not different, the reason why MRTs were different between both sexes was the differences in MTs (peripheral motor functions). 4. PMTs which mean central motor functions (motor pattern generator) were not different for both sexes among the nine , ten and eleven years o1d group , but this function appeared earlier for the female than for the male. However, this function of the male was superior to that of the female from ten years old. From the present results, two different motor functions (motor output and motor pattern generators) were considered which showed the developmental changes of reaction times in two different movement patterns.