RAFAEL F. ESCAMILLA Michael W. Krzyzewski Human Performance Laboratory, Division of Orthopaedic Surgery, Duke University Medical Center, Durham, NC 27710
ESCAMILLA, R. F. Knee biomechanics of the dynamic squat exercise. Med. Sci. Sports Exerc., Vol. 33, No. 1, 2001, pp. 127-141. Purpose: Because a strong and stable knee is paramount toan athlete's or patient's success, an understanding of knee biomechanics while performing the squat is helpful to therapists, trainers, sports medicine physicians, researchers, coaches, and athletes who are interested in closed kinetic chain exercises, knee rehabilitation, and training for sport. The purpose of this review was to examine knee biomechanics during the dynamic squat exercise.Methods: Tibiofemoral shear and compressive forces, patellofemoral compressive force, knee muscle activity, and knee stability were reviewed and discussed relative to athletic performance, injury potential, and rehabilitation. Results: Low to moderate posterior shear forces, restrained primarily by the posterior cruciate ligament (PCL), were generated throughout the squat for all knee flexion angles.Low anterior shear forces, restrained primarily by the anterior cruciate ligament (ACL), were generated between 0 and 600 knee flexion. Patellofemoral compressive forces and tibiofemoral compressive and shear forces progressively increased as the knees flexed and decreased as the knees extended, reaching peak values near maximum knee flexion. Hence, training the squat in the functional range between0 and 500 knee flexion may be appropriate for many knee rehabilitation patients, because knee forces were minimum in the functional range. Quadriceps, hamstrings, and gastrocnemius activity generally increased as knee flexion increased, which supports athletes with healthy knees performing the parallel squat (thighs parallel to ground at maximum knee flexion) between 0 and 100° knee flexion.Furthermore, it was demonstrated that the parallel squat was not injurious to the healthy knee. Conclusions: The squat was shown to be an effective exercise to employ during cruciate ligament or patellofemoral rehabilitation. For athletes with healthy knees, performing the parallel squat is recommended over the deep squat, because injury potential to the menisci and cruciate and collateral ligamentsmay increase with the deep squat. The squat does not compromise knee stability, and can enhance stability if performed correctly. Finally, the squat can be effective in developing hip, knee, and ankle musculature, because moderate to high quadriceps, hamstrings, and gastrocnemius activity were produced during the squat. Key Words: TIBIOFEMORAL, PATELLOFEMORAL, SHEAR FORCE, COMPRESSIVE FORCE,ANTERIOR CRUCIATE LIGAMENT, POSTERIOR CRUCIATE LIGAMENT, MUSCLE ACTIVITY, QUADRICEPS, HAMSTRINGS, GASTROCNEMIUS, KNEE STABILITY
strength and conditioning programs for many sports T that require high levels of strength and power, such as football, track and field, powerlifting, and Olympic weightlifting. The squat primarily strengthens hip, thigh, and back musculature, which are very important musclesin running, jumping, and lifting. It is commonly believed among athletes and coaches that the squat enhances athletic performance and minimizes injury potential. Because the dynamic squat has been classified as a closed kinetic chain exercise (17,58,65,71), it is also appropriate and commonly used in knee rehabilitation settings. Several studies have demonstrated the favorable use of the squatexercise during knee rehabilitation (21,32,39,47,52,58,71), such as after cruciate ligament reconstructive surgery. Consequently, an understanding of knee biomechanics during the squat is helpful to therapists, trainers, sports medicine physicians, 0195-9131/01/3301-0127/$3.00/o
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