THE STRAIN BEHAVIOR OF THE ANTERIOR CRUCIATE LIGAMENT DURING SQUATTING AND ACTIVE FLEXION-EXTENSION - A COMPARISON OF AN OPEN AND A CLOSED KINETIC CHAIN

The effects of weightbearing (closed kinetic chain) and nonweightbeari ng (open kinetic chain) exercises on the biomechanical behavior of an injured anterior cruciate ligament or a healing anterior cruciate liga ment graft are unknown. To understand the effects of these exercises o n the healing graft, we measured the strain behavior of the normal ant erior cruciate ligament in human subjects while they performed squatti ng, a closed kinetic chain exercise, and active flexion-extension of t he leg, an open kinetic chain exercise. The maximum anterior cruciate ligament strain values obtained during squatting did not differ from t hose obtained during active flexion-extension. Also, anterior cruciate ligament strain values obtained during squatting were unaffected by t he application of elastic resistance intended to increase muscle activ ity. These findings indicate that squatting, which produces a substant ial compressive joint force, does not necessarily protect the anterior cruciate ligament more than active flexion-extension of the leg, whic h is characterized primarily by contraction of the dominant quadriceps muscle. These findings also demonstrate that increasing resistance du ring the squat exercise does not produce a significant increase in ant erior cruciate ligament strain values, unlike increased resistance dur ing active flexion-extension exercise.