Preventive Effect of Local Vibrations at Different Frequencies on Human Forearm Muscle Fatigue and Its Mechanism of EEG Neural Network

Objective: To explore the effect of local vibrations at different frequencies on the prevention of forearm muscles fatigue and its mechanism of EEG neural network. Methods: 16 healthy adults were recruited in this study, local vibration(LV) with three frequencies(60, 30, 0 Hz) was performed on the flexor tendons of the subjects' right forearm before muscle fatigue. The 60 Hz and 30Hz were set as the experimental groups, and the 0 Hz was the control group. The maximal voluntary contraction(MVC) force at before and after vibration stimulation, the electromyography(EMG), grip strength and rating of perceived exertion(RPE) during the fatiguing task and electroencephalography(EEG) during resting state immediately after vibration were recorded. Results: The time of muscle fatigue was(154.5±42.9)s(0 Hz),(187.3±60.0)s(30 Hz), and(226.5±65.1)s(60 Hz), respectively, differences between groups were significant with 60 Hz LV>30 Hz LV>0 Hz LV(P<0.05). The sample entropy(SE) of grip strength was 1.62±0.33(0 Hz), 1.60±0.53(30 Hz), and 1.31±0.40(60 Hz), respectively, differences between groups were significant(P<0.05), i.e., 60 Hz LV<30 Hz LV(P<0.05) and 60 Hz LV<0 Hz LV(P<0.05). The normalized RMS(%) of EMG of forearm flexor muscle was37.2%±14.4%(0 Hz), 54.0%±22.9%(30 Hz), and 43.5%±20.0%(60 Hz), respectively, differences between groups were significant with 30 Hz>0 Hz(P<0.05). After LV, the functional brain connectivity between the contralateral hemisphere central and parietal regions in the β3 band showed significant difference(P<0.05) with 60 Hz LV>0 Hz LV(P<0.05), and the functional brain connectivity between the contralateral hemisphere central and ipsilateral hemisphere frontal regions in the β3 band showed significant difference(P<0.05) with 60 Hz LV>30 Hz LV. Significant differences were also found in the functional brain connectivity of contralateral hemisphere central and parietal regions in the alpha band(P<0.05) with 30 Hz LV>0 Hz LV.Conclusions: Conducting 60 Hz or 30 Hz local vibrations on the forearm flexor muscle before exercise can effectively prevent exercise muscle fatigue induced by low-level isometric contraction. However, the effects are different between the two vibration frequencies, that maybe related to the recruitment of motor neurons and functional brain connectivity between the motor cortex and sensory cortex.