The Strain Behavior of the Anterior Cruciate Ligament During Squatting and Active Flexion-Extension: A Comparison of an Open and a Closed Kinetic Chain Exercise

Abstract

The effects of weightbearing (closed kinetic chain) and nonweightbearing (open kinetic chain) exercises on the biomechanical behavior of an injured anterior cru ciate ligament or a healing anterior cruciate ligament graft are unknown. To understand the effects of these exercises on the healing graft, we measured the strain behavior of the normal anterior cruciate ligament in human subjects while they performed squatting, a closed kinetic chain exercise, and active flexion-exten sion of the leg, an open kinetic chain exercise. The maximum anterior cruciate ligament strain values ob tained during squatting did not differ from those ob tained during active flexion-extension. Also, anterior cruciate ligament strain values obtained during squat ting were unaffected by the application of elastic resis tance intended to increase muscle activity. These find ings indicate that squatting, which produces a substantial compressive joint force, does not necessar ily protect the anterior cruciate ligament more than active flexion-extension of the leg, which is character ized primarily by contraction of the dominant quadri ceps muscle. These findings also demonstrate that increasing resistance during the squat exercise does not produce a significant increase in anterior cruciate ligament strain values, unlike increased resistance dur ing active flexion-extension exercise.