Synchronisation of motor firing by vibration during stretch evoked responses of the human wrist flexors.

The wrist was rapidly dorsiflexed while the flexor muscles were being vibrated at 120 Hz. During both the M1 and the M2 responses the EMG showed a series of waves at the vibration frequency. When the vibration was turned off after overlapping with the stretch for only three to four cycles these EMG waves ceased about 30 ms later. Spinal reflexes are thus shown to continue to influence the discharging motoneurones throughout the human M2 "long-latency" response.