Role of Cocontraction in Arm Movement Accuracy

Abstract

Cocontraction (the simultaneous activation of antagonist muscles around a joint) provides the nervous system with a way to adapt the mechanical properties of the limb to changing task requirements—both in statics and during movement. However, relatively little is known about the conditions under which the motor system modulates limb impedance through cocontraction. The goal of this study was to test for a possible relationship between cocontraction and movement accuracy in multi-joint limb movements. The electromyographic activity of seven single- and double-joint shoulder and elbow muscles was recorded using surface electrodes while subjects performed a pointing task in a horizontal plane to targets that varied randomly in size. Movement speed was controlled by providing subjects with feedback on a trial-to-trial basis. Measures of cocontraction were estimated both during movement and during a 200-ms window immediately following movement end. We observed an inverse relationship between target size and cocontraction: as target size was reduced, cocontraction activity increased. In addition, trajectory variability decreased and endpoint accuracy improved. This suggests that, although energetically expensive, cocontraction may be a strategy used by the motor system to facilitate multi-joint arm movement accuracy. We also observed a general trend for cocontraction levels to decrease over time, supporting the idea that cocontraction and associated limb stiffness are reduced over the course of practice.

Evidence for the Flexible Sensorimotor Strategies Predicted by Optimal Feedback Control

“…The only evidence for the energy cost was indirect: it was needed to make our model fit the data. However, other studies have provided more direct evidence: increased muscle cocontraction has been found to yield more accurate movements (Burdet et al, 2001;Gribble et al, 2003), and yet this is not a strategy that subjects normally use, suggesting that they care about energetic efficiency in addition to accuracy. It is also notable that successful optimal control models of full-body movements are predominantly based on energy minimization (Anderson and Pandy, 2001;Pandy, 2001).…”

Biomechanics of recumbent cycling in adolescents with cerebral palsy with and without the use of a fixed shank guide

“…It was anticipated that muscle activity would be altered if the legs were better aligned in the sagittal plane; however, this did not happen. Participants might require more training to optimize muscle patterns and decrease the cocontraction that can accompany a novel task [29]. Participants in this study received 10-20 min of training with the goal of cycling at the two cadences.…”

The use of flexible arm muscle synergies to perform an isometric stabilization task

“…The co-contraction modes may have helped improve performance by stiffening the joints, which is known to help resist perturbations (Gribble et al, 2003) or may be used as a strategy to reach sections of 'feasible' joint torque space which cannot be done by action of a single muscle alone (Valero-Cuevas, 2005). Co-contraction patterns have been seen in individuals with Down's syndrome (Aruin and Almeida, 1997), elderly subjects, and persons with neurological disorders (Woollacott et al, 1988;Woollacott and Burtner, 1996).…”