The effects of ACL injury on lower extremity activation during closed kinetic chain exercise

Injury to the anterior cruciate ligament (ACL) has been suggested to alter the neuromuscular mechanism in the lower extremity. However, conclusive evidence regarding this occurrence has yet to be established during closed kinetic chain exercise. The purpose of this study was to assess differences in muscle activation during slideboard exercise between non-injured, ACL deficient, and ACL reconstructed individuals.

comparative study.

research laboratory.

subjects for this study included 10 healthy, non-injured (NI) individuals, 7 uni-lateral ACL deficient (ACLD) individuals, and 6 uni-lateral ACL reconstructed (ACLR) individuals.

EMG activity was measured from the vastus medialis (VM), vastus lateralis (VL), medial hamstring (MH), lateral hamstring (LH), tibialis anterior (TA), and medial gastrocnemius (MG) muscles during slideboard performance.

EMG for each muscle during each of 6 phases of 1 average slideboard cycle was expressed as a percentage of EMG during a maximal voluntary contraction.

The results demonstrated that during slideboard phase I the VM, VL, and TA muscles generated the greatest amount of activity as compared to the other muscles. Vastus medialis muscle activation was found to be significantly higher than the other muscles in the involved/dominant limb, as compared to the non-involved/non-dominant limb during slideboard phase II. During slideboard phases III-VI, tibialis anterior muscle activation was found to be consistently higher than the other muscles, while hamstring muscle activity was consistently the lowest.

It is concluded that adaptive changes following ACL injury during a dynamic, closed kinetic chain activity such as the slideboard exercise, may be a restoration of a bi-lateral balance in muscle activation.