Abstract
Co-activations of agonist and antagonist muscles are believed to be present in voluntary limb movement. Recent studies indicate that such co-activations are either synergic or dyssynergic. The aims of this study are (1) develop a novel method that can extract both the intensity and frequency information from the recordings of the surface electromyograms (EMGs) of involved muscles, and (2) to investigate if the involved muscles will be under synergic co-activation during voluntary elbow flexion and voluntary forearm pronation for normal subjects and dyssynegic co-activation for patients with radial nerve palsy. We examined six healthy subjects for the experiment of elbow flexion and eleven healthy subjects and four patients with right-arm radial nerve palsy for the experiment of forearm pronation. Experimental results of the healthy group indicated that the surface EMGs of all muscles had no statistically significant changes in fractal dimensions (FDs) and spectral frequencies during passive elbow flexion and forearm pronation. Yet, during the voluntary elbow flexion and the voluntary forearm pronation, the surface EMGs of all muscle groups were temporally synchronized in frequencies with persistent intensities. Hence, all involved muscle groups were in synergic co-activation. Statistical results of the group mean values of FDs during rest versus elbow flexion or forearm pronation also revealed significant difference with P < 0.01 for healthy subjects. As to the group of patients in the experiment of forearm pronation, their EMGs could still have bursting activities, but the synchronized significant frequencies might be lacking or the intensities as indicated from their FDs would not be persistent. Finally, in order to illustrate the advantages of our method, we have compared it with the principal component analysis (PCA) and the detrended fluctuation analysis (DFA). It is believed that this proposed method will have the potential to be a biomarker for evaluating dynamical disease in neuromuscular disorders.