Influence of visual feedback on force-EMG curves from spinally innervated versus trigeminally innervated muscles.

Objective: We compared the influence of visual feedback between spinal and trigeminal muscle activity.

Design: Twelve subjects participated in two tasks: a finger pinch and a tooth clench task and performed a series of muscle activations with visual feedback as a training task and two series without visual feedback as pre- and post-training tasks. Five target force levels at 10%, 20%, 40%, 60% and 80% maximal voluntary contraction were performed in each series for both tasks. During all series electromyographic (EMG) activity and force were recorded. Target force-actual force and target force-EMG curves were compared with and without visual feedback for both tasks. The variability in each series was determined as the coefficient of variation (CV) from the EMG and force recordings.

Results: Although positive linear relationships were found between the target force level and the actual force value, and target force level and root mean square (RMS)-EMG amplitude from the tooth clenching task, the curves calculated from the finger pinch task were not completely linear. CVs of the actual force value and CVs of the RMS-EMG amplitude in both masseter and temporalis muscles were significantly influenced by visual feedback (P<0.001). However, the CVs of the RMS-EMG amplitude in right abductor pollicisbrevis and right first dorsal interosseous muscles were not significantly influenced by the three series.

Conclusions: The influence of visual feedback was different between spinally innervated and trigeminally innervated muscles, and the specific mechanism of force execution from muscle activity appears to be different between the tasks.