Discussion
abduction of the shoulder joint, tremor, Tremors, tremors, muscle hypertrophy
In the arming phase of archery shooting, fast muscle fibre activity is required to pull the strings strongly, and in the sighting phase, the target must be aimed while keeping the strings pulled out. In this study, we hypothesized that the activity of slow muscle fibres was necessary to reduce bow tremor in the sighting phase and identified an exercise and verified its effect by performing randomized controlled trials. A comparison of the exercise methods under the four conditions showed that the side bridge exercise, in which the trunk is tilted 40°, is the condition with the least tremor and the greatest trunk inclination. Therefore, we hypothesized that a side bridge at a 40° inclination could be performed with less tremor in the sighting phase and examined the effect of 4-week training with this exercise on tremor.The results suggested that exercises aimed at reducing tremors during the shooting action in archery are effective when the exercise itself is performed with a load that does not cause tremors to appear. The participants also showed a reduction in the MdPF of the middle deltoid after 4 weeks of exercise. Thus, side-bridge exercise performed with a trunk angle adjusted to avoid the appearance of tremors appeared to reduce the tremor in the sighting phase of archery and also changed the activity of the middle deltoid muscle. The activity of motor units that control slow muscle fibres has been shown to mainly reflect low-frequency components, while that of fast-muscle fibres reflects high-frequency components [Previous studies have shown that nervous system factors change up to 4 weeks after the commencement of exercise, and that muscle hypertrophy causes muscle strengthening 8 weeks after starting the exercise [Tremors can be divided into rest and action tremors based on their occurrence, and tremors that occur during exercise can be classified into postural, isometric, and kinetic tremors [The exercise performed in this study can be performed with 90° abduction of the shoulder joint, which is the same as the archery target posture, and the angle of the side-bridge exercise is defined from the trunk inclination, making it a completely new exercise unlike the previously performed side bridge. In addition, the exercise duration was set to 1 min per set, and five sets were performed. In previous studies, male college students were reported to perform a side bridge for an average period of 97 s, and in other previous studies, the exercise was performed as long as possible [The limitations of this study are as follows. First, the participants were not professional archers; therefore, the effectiveness of the intervention exercise on the actual shooting movements of professional archers was unclear. However, to verify the effect of an exercise in one sport, it is desirable to assess the exercise in participants who do not perform other sports, and the present study met this criterion. Second, the side-bridge exercise assessed in this study was performed at a trunk angle at which tremor did not occur, but it was unclear which of the other tremor-inducing conditions was the most effective in reducing tremors. Among the exercise conditions evaluated in this study, cond4 can be excluded because it is difficult to perform and it is difficult to set the exercise time for this condition. Third, the effect of the exercise was judged solely on the basis of the information obtained by the accelerometer and the electromyogram, and the related physiological changes are unknown. The muscles evaluated in this study were the four muscles around the shoulder joint. Since side-bridge exercise is also used for core muscle training, other muscle groups may have influenced the results of this study, but their influence could not be determined from the results of this study.