A burst-superimposition technique was used to assess the strength of the
quadriceps femoris muscle in three groups of patients. Group 1 comprised
twenty patients who had had a torn anterior cruciate ligament of the knee
and had a reconstruction of the ligament one to six months after the
injury. Group 2 comprised twelve patients who had had a torn anterior
cruciate ligament for an average of three months (a subacute tear). Group 3
comprised eight patients who had had a torn anterior cruciate ligament for
an average of two years (a chronic tear). The patients in Groups 2 and 3
had not had an operation for the torn ligament. The patients in Groups 1
and 3 had no evidence of failure of activation of the involved quadriceps,
but nine of the twelve patients in Group 2 had reflex inhibition of
contraction of the muscle.