Redundancy or heterogeneity in the electric activity of the biceps brachii muscle? Added value of PCA-processed multi-channel EMG muscle activation estimates in a parallel-fibered muscle

Abstract

Conventional bipolar EMG provides imprecise muscle activation estimates due to possibly heterogeneous activity within muscles and due to improper alignment of the electrodes with the muscle fibers. Principal component analysis (PCA), applied on multi-channel monopolar EMG yielded substantial improvements in muscle activation estimates in pennate muscles. We investigated the degree of heterogeneity in muscle activity and the contribution of PCA to muscle activation estimates in biceps brachii (BB), which has a relatively simply parallel-fibered architecture. EMG-based muscle activation estimates were assessed by comparison to elbow flexion forces in isometric, two-state isotonic contractions in eleven healthy male subjects. Monopolar EMG was collected over the entire surface of the BB with about 63 electrodes. Estimation quality of different combinations of EMG channels showed that heterogeneous activation was found mainly in medio-lateral direction, whereas adding channels in the longitudinal direction added largely redundant information. Multi-channel bipolar EMG amplitude improved muscle activation estimates by 5-14% as compared to a single bipolar. PCA-processed monopolar EMG amplitude yielded a further improvement of (12-22%). Thus multi-channel EMG, processed with PCA, substantially improves the quality of muscle activation estimates compared conventional bipolar EMG in BB.

Brachialis muscle activity can be assessed with surface electromyography

“…1) did not show more similar values than the coefficients to the more distant electrodes. When regarding the activity of the four sites within the BB no significant difference between these four sites in the association to elbow flexion or forearm supination was apparent (see , although previous studies using intramuscular or multichannel EMG recordings indicated an inhomogeneous activity during the same type of contraction as in the current study (Perot et al, 1996;Staudenmann et al, 2013;ter Haar Romeny et al, 1984;van Zuylen et al, 1988). This discrepancy may be related to the limitation of conventional bipolar EMG which cannot extract muscular activity with the same precision as multichannel EMG (Staudenmann et al, 2010(Staudenmann et al, , 2013.…”

“…Recordings of the BB were obtained from the proximal and distal portion of the two muscle heads, as distinct EMG activities of the two muscle parts were observed for specific contractions (Perot et al, 1996;Staudenmann et al, 2013;ter Haar Romeny et al, 1984;van Zuylen et al, 1988). Furthermore, the activity of the BR was recorded over the medial and lateral sides of the distal upper arm where the muscle becomes superficial, and the electrodes over the BRR were attached as displayed in Fig.…”

Increase in heterogeneity of biceps brachii activation during isometric submaximal fatiguing contractions: a multichannel surface EMG study

“…Multichannel and intramuscular EMG studies have shown that muscle activity can show some spatial variability during brief muscle contractions (Falla and Farina 2007b;Farina et al 2008;Hedayatpour et al 2008;Holtermann et al 2008;Staudenmann et al 2009Staudenmann et al , 2013ter Haar Romeny et al 1984;van Zuylen et al 1988) and that activity can alternate within a muscle during sustained and repetitive contractions (Sirin and Patla 1987;van Dieën et al 1993). With the progressive recruitment of the motor unit pool during a sustained submaximal contraction, however, it can be expected that the distribution of surface EMG amplitudes would become more homogeneous as motor units with larger territories are recruited (Milner-Brown and Stein 1975).…”

“…The findings to date, however, have not characterized the changes in the spatial distribution of the entire muscle due to limitations in the size of the high-density EMG grids. Moreover, multiple bipolar EMG recordings provide less accurate estimates of muscle activity compared with processing the same monopolar channels with principal component analysis (PCA; Staudenmann et al 2006Staudenmann et al , 2013. It is expected that the active motor units within a muscle are represented with a higher accuracy when processing multiple monopolar EMG with PCA (cf.…”

“…Muscle activity was characterized with multiple surface electrodes distributed over the entire muscle (cf. Staudenmann et al 2013). Monopolar EMG signals were processed with PCA to obtain more representative spatial information of the entire muscle activity (Staudenmann et al 2006).…”