High‐pass filtering surface EMG in an attempt to better represent the signals detected at the intramuscular level

Abstract

Surface electromyography (EMG) is often used to represent activation profiles of the underlying musculature. The purpose of this study was to assess the potential of high-pass (HP) filtering to improve the matching of surface EMG signals to those signals recorded intramuscularly. EMG was recorded at the skin surface over the infraspinatus and supraspinatus muscles as well as from fine-wire electrodes placed in the infraspinatus, supraspinatus, and teres minor muscles. The surface EMG signals were HP-filtered at 18 cutoff frequencies (0-510 HZ in 30 HZ increments), and the time-histories were correlated with the signals from the wire electrodes. HP filtering did not significantly alter the correlated muscle activation waveform relationship between the surface and wire signals until cutoffs reached 240 HZ. HP filtering of the surface signals did not improve the representation of the muscle fiber-level activation profile, but the results suggest that enough information resides in the high-frequency components of the signal to reproduce the activation time-history profile of the muscle.

Cortical mapping of the infraspinatus muscle in healthy individuals

“…One of its primary functions is to depress the humeral head during arm elevation, which prevents subacromial impingement. The infraspinatus is the only RC muscle for which there are no other muscles located between its own muscle tissue and the skin [2]. Therefore, it provides the most direct recording of all RC muscles.…”

“…EMG activity of the supraspinatus and teres minor could also be evaluated by using surface electrodes, providing the feasibility of evaluating their M1 representations using TMS; however, EMG crosstalk is a bigger issue in this case. The site for recording the supraspinatus using surface electrodes is located over a window where the tendon of the trapezius lies between the muscle and the skin [2]. Therefore, as suggested by Brown et al [2], the recording may pick up some end-propagating activation from the trapezius.…”

“…The site for recording the supraspinatus using surface electrodes is located over a window where the tendon of the trapezius lies between the muscle and the skin [2]. Therefore, as suggested by Brown et al [2], the recording may pick up some end-propagating activation from the trapezius. As for the teres minor, it lies deep into the infraspinatus and is assessed from the infraspinatus surface electrode site [2].…”

“…Aside from the infraspinatus, RC muscles are very difficult, if not impossible to access using surface electrodes. Electromyographic (EMG) activity of the infraspinatus muscle can be recorded using surface electrodes over a small window overlying the infraspinatus process where there are no other muscles located between its own muscle tissue and the skin [2]. Brown et al have shown that EMG signals obtained using skin surface electrodes have a strong correlation with the ones using fine-wire electrodes, showing the validity of surface EMG recording of this muscle [2].…”

Shoulder muscle activity during the modified dynamic relocation test and side-lying shoulder external rotation: a cross-sectional study on asymptomatic individuals

“…33,34 An alternative for surface electrodes is the use of indwelling electrodes, which have far smaller receptive fields but may be limited in their ability to accurately represent whole-muscle activation levels. [34][35][36] Despite its spatial limitation, SEMG has been commonly used for recording rotator cuff muscle activity. [19][20][21]37 One of the main criticisms for its use is the potential crosstalk from adjacent muscles.…”