Co-contraction

The simultaneous activation of antagonistic muscles — for example, the biceps and triceps firing at the same time. Some co-contraction is normal and useful for joint stability, but involuntary or excessive co-contraction is common in conditions such as spasticity, cerebral palsy, stroke, and some spinal cord injuries. In EMG-based input systems, unintended co-contraction can simultaneously trigger opposing commands (e.g., both "left" and "right" steering), making stable control difficult for users with certain neurological conditions.