Methodological aspects of SEMG recordings for force estimation – A tutorial and review

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

“…The larger difference in RMSD between proximal and distal configurations with PCA than with the bipolar EMG, suggests that PCA processing is more representative of the motor units within the muscle, probably also of deeper motor units (e.g. Staudenmann et al, 2010).…”

“…We did not expect this substantial improvement with PCA over a parallel-fibered muscle such as BB, because bipolar electrodes can be aligned to the fiber direction. When discarding the first components of monopolar EMG signals with PCA, this acts similarly to a bipolar configuration, which per definition also discards common information, but PCA is unbiased in respect to the muscle fiber direction (Staudenmann et al, 2006(Staudenmann et al, , 2010. However, BB may have a more complex architecture than commonly assumed with an overall fusiform shape and obliquely oriented fibers at the distal portion of BB (Pappas et al, 2002).…”

“…Another aspect, as already mentioned above, is that PCA may be more representative of all active motor units in the muscle (cf. Staudenmann et al, 2010). Accordingly, not only BB can be better represented in PCA-processed EMG, but also information form brachialis is expected to be better represented over the distal portion of BB as using a bipolar EMG.…”

“…It has to be realized, however, that the representativeness of the active (heterogeneous) motor unit potentials in the surface EMG is even more important than problems of crosstalk (e.g. Staudenmann et al, 2010).…”

“…Importantly, activity can be heterogeneous within muscles during voluntary contractions, as was shown with multi-channel EMG (Eriksson et al, 1984;Holtermann et al, 2005;Staudenmann et al, 2005Staudenmann et al, , 2009avan Zuylen et al, 1988, Vieira et al, 2011Wolf et al, 1998), as well as with ultrasound imaging (Bojson-Moller et al, 2004;Darby et al, 2012;Finni et al, 2003;Pappas et al, 2002). Thus information obtained by a single bipolar EMG will not be representative for the entire muscle and consequently muscle activation estimates derived from multi-channel EMG (collecting from different parts of the muscle) are superior to those derived from a single bipolar EMG (Staudenmann et al, 2010).…”