Effects of handgrip contraction modes on intermuscular coordination quantified by wavelet-based EMG-EMG coherence between 2 and 300 Hz.

Handgrip exercise is a common rehabilitation intervention but the effects of contraction modes (isometric and dynamic contractions) on modulating intermuscular coordination have not been investigated. Furthermore, coherence has been assessed at the $\alpha$ , $\beta$ , $\gamma$ bands of surface electromyography (EMG) and ignores the frequency over 60 Hz. The objective of this study was to assess the effects of muscle contraction modes on intermuscular coordination using wavelet-based EMG-EMG coherence. Sixteen healthy adults performed isometric handgrip (IHG) at 30% of maximal voluntary contraction (MVC) for 90 s and dynamic handgrip (DHG) at 30% MVC at a cadence of 1 Hz for 180 s in a random order with a 20-min rest. Two exercise modes have a similar exercise volume. EMG signals were recorded from the flexor digitorum superficialis (FDS), extensor carpi radialis (ECR), flexor carpi ulnaris (FCU), and extensor carpi ulnaris (ECU) and wavelet coherence of muscle pairs of 4 muscles was computed in seven frequency bands, including 2-5, 8-12, 15-35, 35-60, 60-100, 100-200, and 200-300 Hz. The results showed that IHG and DHG evoked different changes in muscle activation and intermuscular coordination. IHG evoked lower muscle activation compared to DHG. DHG resulted in a significant muscle activation and coherence in 2-5 and 8-12 Hz. IHG resulted in a significant muscle activation and coherence in 15-35, 35-60, and 60-100 Hz compared to DHG. The findings of this study indicate that the mode of handgrip exercise affects the muscle activation and intermuscular coordination between 2 and 300 Hz of EMG signals.