Document Title: Stuart-AJSM-Nov96.shtml
Article Title: Comparison of Intersegmental Tibiofemoral Joint Forces and Muscle Activity During Various Closed Kinetic Chain Exercises
Authors: Michael J. Stuart, MD, Dwight A. Meglan, PhD, Gregory E. Lutz, MD, Eric S. Growney, and Kai-Nan An, PhD
Publication: American Journal of Sports Medicine, Baltimore, Maryland
Date: November 1996
Volume 24, Number 6, pages 792-799
Keywords: ACL rehabilitation, closed-kinetic-chain exercises, anterior-drawer shearing, sagittal-plane shearing, risk to normal knee versus risk to ACL-injury-history knee.

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Comments: Using a well-equipped biomechanics laboratory, the authors used a motion analysis system (three-dimensional infrared video cameras and floor-mounted force plates) to determine the forces on the knee during several closed-kinetic-chain exercises: the power squat, the front squat, and the lunge. (Closed-kinetic-chain exercises involve the foot bearing weight throughout the exercise movement.) They found that the aforementioned exercises do not produce harmful anterior-drawer forcing (sagittal-plane shearing of tibia with respect to femur) of a magnitude sufficient to be worrisome for ACL-intact knees. Additionally, the note that harmful ACL shearing forces are mitigated by flexion the knee and trunk to more than 30 degrees. Furthermore, especially during squat-type exercises, the positional interrelationships between the hip, knee, and ankle are critical, since foot placement engenders substantial changes in ACL (or ACL-graft) forces throughout the knee's range of motion. However, they warn that additional research is needed in order to ascertain whether these particular free-weight closed-kinetic-chain exercises are safe for ACL-deficient, ACL-compromised, or recently ACL-reconstructed knees. The three exercises studied herein, as depicted in Figure 1 (and especially if done with a barbell weighing 50 pounds or more), could potentially be unsafe for a person with a recently injured or freshly ACL-reconstructed knee to pursue without specific recommendations and guidance from a knee-experienced orthopedic surgeon or a knee-experienced physiotherapist.

ABSTRACT

The purpose of this study was to analyze intersegmental forces at the tibiofemoral joint and muscle activity during three commonly prescribed closed kinetic chain exercises: the power squat, the front squat, and the lunge. Subjects with anterior cruciate ligament-intact knees performed repetitions of each of the three exercises using a 223-N (50-pound) barbell. The results showed that the mean tibiofemoral shear force was posterior (tibial force on femur) throughout the cycle of all three exercises. The magnitude of the posterior shear forces increased with knee flexion during the descent phase of each exercise. Joint compression forces remained constant throughout the descent and ascent phases of the power squat and the front squat. A net offset in extension for the moment about the knee was present for all three exercises. Increased quadriceps muscle activity and decreased hamstring muscle activity are required to perform the lunge as compared with the power squat and the front squat. A posterior tibiofemoral shear force throughout the entire cycle of all three exercises in these subjects with anterior cruciate ligament-intact knees indicates that the potential loading on the injured or reconstructed anterior cruciate ligament is not significant. The magnitude of the posterior tibiofemoral shear force is not likely to be detrimental to the injured or reconstructed posterior cruciate ligament. These conclusions assume that the resultant anteroposterior shear force corresponds to the anterior and posterior cruciate ligament forces.

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