Muscle responses during sudden falls in man.

1. E.m.g. activity in soleus during an unexpected fall is found to be more complex than that described by Melvill Jones & Watt (1971b). After a silent period of about 80 msec an initial peak of activity lasts until about 100 msec after release. In falls from sufficient heights a second peak of activity occurs before landing. 2. The initial peak of activity is found in muscles throughout the body and is absent during falls in which the subject releases himself. It is suggested that this initial peak is a startle response to release and on landing during the initial peak any deceleration due to tension in the leg muscles is in part coincidental. 3. The second peak of activity is found in muscles of the lower limbs. Its timing is related to the timing of landing. It is suggested that this is the activity concerned in thhe voluntary control of landing. 4. No initial peak of activity could be recorded in two patients with absent labyrinthine function.