Procedures

In relaxed upright positions, participants performed rapid 135° flexion, 135° abduction, and 45° extension of the shoulder on the dominant hand side with and without anticipation of the movement starting time. In the shoulder joint movements with anticipation of the movement starting time, participants moved their shoulder joint following a 3-s countdown by the examiner. The countdown was performed according to the metronome rhythm set at 60 beats/min. The timing of the count “1” by the examiner was recorded in the EMG data using the trigger signal. In the shoulder joint movements without anticipation of the movement starting time, participants moved their shoulder joint after a light stimulus. The light was placed 3 m ahead of participants, and the timing of the light emission was recorded in the EMG data by the trigger signal. Participants practiced three to five times before each trial was recorded. Each trial was recorded three times, while the examiners confirmed the relaxed condition of participants on the EMG monitor during the countdown and before the light stimulus. The trials were randomly conducted. The rest interval between each trial was at least 1 min.