Cross-Recurrence Quantification Analysis for Inter-Muscular Coordination during Power Grip at Different Force Levels.

This study aimed to examine the dynamical coordination across muscles during power grip at different force levels. Twenty-four healthy volunteers (12 males, 12 females) participated in this experiment. Subjects were instructed to grip a hydraulic hand dynamometer and produce forces at 30%, 50%, 70% Maximal Voluntary Contractions (MVC) for at least 10s, respectively. Surface electromyography (sEMG) signals were simultaneously recorded from eight muscles, including brachioradialis (BR), flexor carpi ulnaris (FCU), flexor carpi radialis (FCR), extensor digitorum communis (EDC), flexor digitorum superficialis (FDS), abductor pollicis brevis (APB), first dorsal interosseous (FDI) and abductor digiti minimi (ADM). A cross-recurrence quantification analysis (CRQA) was applied to analyze the sEMG signals by both visualization and quantifications. Results showed that percentage of determinism (%DET) and percentage of entropy (%ENT) of the extrinsic muscle pairs were augmented with increased force levels and had a weak but positive correlation. For intrinsic muscle pairs, the %DET and %ENT increased with force levels but the difference is not or less statistically significant. These results showed that the intermuscular coordination would be alter with force output increased. For the right-handers, the values of intrinsic muscles couplings in right hand were lower than left hand, because less coupled intrinsic muscles contribute to finger dexterity; the reason why the values of extrinsic muscles couplings in right hand were greater than left hand was stronger couplings of extrinsic muscles produced higher synergistic force.