Correlations between ball rotation rime and electromyography (EMG) variability.

(A–C) Spearman’s correlation coefficient between the ball rotation time and coefficient of variation (CV) of EMG on-phase duration for the abductor pollicis brevis (APB) (A), first dorsal interosseous (FDI) (B), and extensor digitorum (ED) (C) muscles. (D–F) Spearman’s correlation coefficient between the ball rotation time and CV of EMG on-phase area for the APB (D), FDI (E), and ED (F) muscles. Each closed circle represents the data for a single trial in one participant. The data for a total of 30 trials per participant are presented. n = 1110, 1110, and 1080 for APB, FDI, and ED, respectively.