Muscle co-contraction during adaptation to dynamic perturbations

In this study, participants performed center-out reaches to targets under the influence of a velocity dependent force field. They were assigned to one of two groups based on the type of perturbation: i) abrupt, and ii) gradual. The abrupt group was exposed to a force field of 20 Nm-1s whereas the gradual group was exposed to a force field that increased from 5 to 20 Nm-1s in increments of 5 Nm-1s every 52 trials. Muscle co-contraction was measured during the trials using two methods: i) Co-contraction Index, and ii) Global EMG. Our results suggest that the gradual group displayed a tendency to co-contract more during exposure to the force field. Post-exposure, the aftereffects remained for a short period of time with the gradual group tending to co-contract more. During the later part of post-exposure, no difference was seen between the two groups. In combination with the previously analysed kinematic data these results indicate that internal model acquisition and adaptation may be facilitated by muscle co-contraction and exposure to gradual dynamic perturbations as compared to abrupt dynamic perturbations.