Startle responses recorded in the leg of man.

The EMG pattern of startle reactions in the leg was studied in man using a 100 msec, 1 kc/sec squre wave tone burst of 114 dB as the auitory stimulus. At rest, 74 responses were recorded in the ankle flexor tibialis anterior (TA) and 23 in the ankle extensor gastrocnemius (G) with a significantly different mean latency of 151 and 123 msecrespectively. During tonic extension or flexion of the ankle, the EMG response in TA or G consisted in a burst of activity superimposed on the voluntary EMG at a latency of approximately 150 msec after the onset of the tone burst and followed, at 200 msec, by a period of EMG silence lasting close to 100 msec.