Loss of function of quadriceps femoris muscle after extensive knee injuries by voluntary activation deficit

The aim of the study was to investigate the ability to activate the quadric eps femoris muscle voluntarily in patients after severe knee injuries and i t's influence on muscle function. 33 male patients after ACL-rupture with c oncomitant injuries were investigated with a twitch-interpolation-method to determine the maximal voluntary contraction force (MVC) and the ability to activate the quadriceps muscle voluntarily. The results were compared to a previously investigated group of patients after isolated ACL-rupture and t o an aged-matched control group. The patients with extensive knee injuries presented a significant higher de ficit of voluntary quadriceps muscle activation on the injured (78.8+/-2.09 %, mean+/-SEM) and equally on the uninjured side (78.9+/-1.91%) compared to the patients after isolated ACL-rupture and to controls. A minor MVC-defic it of the patients quadriceps muscle of the uninjured side could be explain ed by the voluntary activation deficit alone, the major MVC deficit of the injured side by muscle atrophy and a voluntary activation deficit. The acti vation deficit is probably the underlying reason for persisting muscle wast ing and weakness despite intensive physiotherapy especially in patients wit h concomitant injuries in addition to an ACL-rupture.