Functional connectivity between core and shoulder muscles increases during isometric endurance contractions in judo competitors

The aim of this study was to assess the surface electromyogram (SEMG) changes within and between muscles of the torso and shoulder region during static endurance contraction in elite judokas. We hypothesized an increased functional connectivity of muscles from the shoulder and torso regions during sustained isometric contraction. Twelve healthy, right-handed judo competitors participated in the study. The SEMG signals from the dominant trapezius (upper, middle and lower part), deltoideus anterior, serratus anterior, and pectoralis major muscles were recorded during isometric endurance contraction consisting of bilateral arm abduction at 90A degrees. The normalized mutual information (NMI) was computed between muscle pairs as an index indicating functional connectivity. The NMIs increased significantly during endurance test for 10 of the 15 muscle pairs (P < 0.001). We concluded that the increases in NMIs highlighted functional changes in the interplay between core and shoulder muscles during an endurance contraction in elite judokas.