Low-frequency component of rectified EMG is temporally correlated with force and instantaneous rate of force fluctuations during steady contractions.

INTRODUCTION

The usefulness of surface EMG for assessing motor output variability during steady contraction is unclear. The purpose of this study was to examine the temporal correlation in signal characteristics between low-frequency components of full-wave rectified EMG (with or without high-pass filtering before rectification) and force fluctuations or the instantaneous rate of force fluctuations (dF/dt) during steady contractions.

METHODS

Fourteen young adults produced steady force with the first dorsal interosseus muscle at various intensities. Cross-correlation functions were calculated between the following signals: <5 Hz: force, dF/dt, and rectified EMG with or without high-pass filtering at 300 Hz before rectification.

RESULTS

Rectified EMG correlated better with dF/dt compared with force itself, and high-pass filtering of interference EMG before rectification improved the temporal correlation.

CONCLUSIONS

The low-frequency component of rectified EMG following high-pass filtering may provide temporal information on the instantaneous rate of force fluctuations during steady contractions.