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

Abstract

Staudenmann D, van Dieën JH, Stegeman DF, Enoka RM. Increase in heterogeneity of biceps brachii activation during isometric submaximal fatiguing contractions: a multichannel surface EMG study. J Neurophysiol 111: 984 -990, 2014. First published December 11, 2013 doi:10.1152/jn.00354.2013.-The effects of fatigue emerge from the beginning of sustained submaximal contractions, as shown by an increase in the amplitude of the surface electromyogram (EMG). The increase in EMG amplitude is attributed to an augmentation of the excitatory drive to the motor neuron pool that, more importantly than increasing discharge rates, recruits additional motor units for the contraction. The aim of this study was to determine whether the spatiotemporal distribution of biceps brachii (BB) activity becomes more or less heterogeneous during a fatiguing isometric contraction sustained at a submaximal target force. Multiple electrodes were attached over the entire BB muscle, and principal component analysis (PCA) was used to extract the representative information from multiple monopolar EMG channels. The development of heterogeneity during the fatiguing contraction was quantified by applying a cluster algorithm on the PCA-processed EMG amplitudes. As shown previously, the overall EMG amplitude increased during the sustained contraction, whereas there was no change in coactivation of triceps brachii. However, EMG amplitude did not increase in all channels and even decreased in some. The change in spatial distribution of muscle activity varied across subjects. As found in other studies, the spatial distribution of EMG activity changed during the sustained contraction, but the grouping and size of the clusters did not change. This study showed for the first time that muscle activation became more heterogeneous during a sustained contraction, presumably due to a decrease in the strength of common inputs with the recruitment of additional motor units.

The extraction of neural strategies from the surface EMG: an update

“…In addition to their use for EMG decomposition, high-density electrode systems have also been used to map the electrical activity in muscle (64). This approach can provide robust force estimators from EMG amplitude (96), characterize the adjustments during fatiguing contractions (38,97), and identify details about muscle architecture (67). In the present review, however, we focus only on the use of high-density EMG technology for decomposing the signal into individual trains of motor unit action potentials.…”

Ankle muscle tenotomy does not alter ankle flexor muscle recruitment bias during locomotor‐related repetitive limb movement in late‐stage chick embryos

“…Normalized TA integrated amplitude during RLMs under all conditions was least in the absence of LG activity and greatest when LG was consistently recruited. Given that burst amplitude is an indicator of excitatory neural drive (Farina, Merletti, & Enoka, ; Staudenmann, van Dieen, Stegeman, & Enoka, ), we recently proposed that amplitude scaling and consistent flexor bursting across all levels of drive are indicative of an excitatory drive favoring flexor motor pools during RLMs (Sun & Bradley, ). Thus, current results lead us to conclude that muscle afference does not significantly contribute to the flexor bias in neural drive during RLMs in E20 chicks.…”

Differences in flexor and extensor activity during locomotor‐related leg movements in chick embryos

“…Vertical scales equal 125 μV of neural drive (Farina, Merletti, & Enoka, 2004;Staudenmann, van Dieen, Stegeman, & Enoka, 2014). Asterisks note cycles in which CF activity failed to meet burst criteria.…”

“…In previous work, it was established that increases in EMG amplitude are attributable to increases in excitatory drive to motor pools (Farina et al, 2004;Staudenmann et al, 2014). In previous work, it was established that increases in EMG amplitude are attributable to increases in excitatory drive to motor pools (Farina et al, 2004;Staudenmann et al, 2014).…”