A simple test of muscle coactivation estimation using electromyography

Abstract

In numerous motor tasks, muscles around a joint act coactively to generate opposite torques. A variety of indexes based on electromyography signals have been presented in the literature to quantify muscle coactivation. However, it is not known how to estimate it reliably using such indexes. The goal of this study was to test the reliability of the estimation of muscle coactivation using electromyography. Isometric coactivation was obtained at various muscle activation levels. For this task, any coactivation measurement/index should present the maximal score (100% of coactivation). Two coactivation indexes were applied. In the first, the antagonistic muscle activity (the lower electromyographic signal between two muscles that generate opposite joint torques) is divided by the mean between the agonistic and antagonistic muscle activations. In the second, the ratio between antagonistic and agonistic muscle activation is calculated. Moreover, we computed these indexes considering different electromyographic amplitude normalization procedures. It was found that the first algorithm, with all signals normalized by their respective maximal voluntary coactivation, generates the index closest to the true value (100%), reaching 92 ± 6%. In contrast, the coactivation index value was 82 ± 12% when the second algorithm was applied and the electromyographic signal was not normalized (P < 0.04). The new finding of the present study is that muscle coactivation is more reliably estimated if the EMG signals are normalized by their respective maximal voluntary contraction obtained during maximal coactivation prior to dividing the antagonistic muscle activity by the mean between the agonistic and antagonistic muscle activations.

Sex differences in time to task failure during early pubertal development

“…The coactivation index takes into account normalized activation levels of both agonist and antagonist muscle and has been shown to be more accurate than using a simple coactivation ratio. 33 Our findings indicate that girls at T2 and T3 showed greater antagonist coactivation than boys. In addition, coactivation levels were not different in girls across Tanner stages 1-3, whereas they became successively lower for boys in T2 and T3 compared with T1 boys.…”

“…Before this study, early pubertal sex differences in coactivation during fatiguing submaximal contractions with the elbow flexor muscles had not been quantified. The coactivation index takes into account normalized activation levels of both agonist and antagonist muscle and has been shown to be more accurate than using a simple coactivation ratio . Our findings indicate that girls at T2 and T3 showed greater antagonist coactivation than boys.…”

Quantifying thigh muscle co-activation during isometric knee extension contractions: Within- and between-session reliability

“…The first two rudimentary methods were the semi-quantitative estimates of EMG magnitude [Frost et al, 1997] and the agonist-to-antagonist ratio of EMG activity utilizing millivolts of electrical activity [Damiano et al, 2000; Fung et al, 1989]. The limitations of these two methods led to the adoption of more robust techniques that normalized the EMG amplitude for each of the agonist and antagonist muscle groups to the respective maximum voluntary contraction values (MVC; [Ervilha et al, 2012; Knutson et al, 1994]). The last and more recent method for the calculation of the CI quantified the antagonist moment using mathematical modeling of the EMG/joint torque relationship, but with controversial applicability due to changes in the slope attributable to evolution of the firing frequency and recruitment across the range of muscle activation [Merletti et al, 2004].…”

Effect of Ankle Brace on the Activity and Co-Contraction of Ankle Muscles During Single-Leg Landing

“…To reduce electrical interferences from external sources, the signals were filtered by a bandwidth Butterworth fourth-order filter of 10-500 Hz and a band-stop filter of 50 Hz. The Co-Contraction Index (CCI) [11] was used to represent ankle-dorsiflexor and extensor (TA and GL), and ankle invertor and evertor (TA and PL) muscles cocontraction.…”