Frequency analysis of the EMG from the quadriceps of anterior cruciate ligament deficient individuals.

A bilateral comparison of the peak torque generated by the quadriceps muscles during isokinetic muscle action at a joint angular velocity of 180 deg/sec was undertaken in 17 subjects with chronic anterior cruciate ligament (ACL) deficiency. The results allowed subjects to be separated into minimal and maximal deficit groups. A frequency analysis of the electromyographic signals of the vasti lateralis obtained during the peak torque tests was then undertaken. The results showed that the median frequency of the ACL deficient limb in the maximal deficit group was significantly (p < 0.05) decreased compared to the median frequency of the uninvolved limb and both limbs of the minimal deficit group. These results suggested that type II muscle fibre atrophy had occurred. The frequency analysis of EMG may provide a noninvasive technique of measuring relative fibre atrophy differences between legs.