The influence of low-intensity resistance training combined with neuromuscular electrical stimulation on autonomic activity in healthy adults: A randomized controlled cross-over trial

Background: Low-intensity resistance training (RT) combined with neuromuscular electrical stimulation (NMES) is one method of exercise to improve the deterioration of physical function. However, it is unclear whether low-intensity RT combined with NMES (RT + NMES) can be safely implemented.

Objective: This study aimed to examine the influence of low-intensity RT + NMES on autonomic activity and cardiovascular responses in healthy adults.

Methods: This study was an open-label, randomized controlled cross-over trial. The exercise intensity of isometric knee extension RT was set to 40% of the maximum voluntary contraction (peak torque). NMES was adjusted to a biphasic asymmetrical waveform with the frequency maintained at 50 Hz and a phase duration of 300 $\mu$ s. The difference in the change in autonomic activity and cardiovascular responses was compared by assessing heart rate variability, blood pressure, and heart rate during RT and $\text{RT}+\text{NMES}$ .

Results: Twenty healthy male college students (mean age $21.0\pm 0.6$ years) participated in this study. The ratio of low- and high-frequency components of heart rate variability, systolic blood pressure, and heart rate increased during exercise in the RT and $\text{RT}+\text{NMES}$ sessions ( $P<$ 0.05). There were no significant differences in autonomic activity and cardiovascular responses throughout the sessions during RT and $\text{RT}+\text{NMES}$ .

Conclusion: In conclusion, our results demonstrated that low-intensity $\text{RT}+\text{NMES}$ was safe and did not induce excessive autonomic and cardiovascular responses in healthy adults.