RAFAEL F. ESCAMILLA, GLENN S. FLEISIG, NAIQUAN ZHENG, JEFFERY E. LANDER, STEVEN W. BARRENTINE, JAMES R. ANDREWS, BRIAN W. BERGEMANN, and CLAUDE T. OORMAN, III
Michael W. Krzyzewski Human Performance Laboratory, Division of Orthopaedic Surgery and Duke Sports Medicine, Duke University Medical Center, Durham, NC 27710; American Sports Medicine Institute, Birmingham, AL 35205;Department of Sports Health Science, Life University, Marietta, GA 30060; and Department of Exercise Science, Campbell University, Buies Creek, NC 27506
Effects of technique variations on knee biomechanics during the squat and leg press. Med. Sci. Sports Exerc., Vol. 33, No. 9, 2001, pp. 1552–1566.
Purpose: The specific aim of this project was to quantify knee forces and muscle activity while performing squat and leg press exercises with technique variations.
Methods: Ten experienced male lifters performed the squat,a high foot placement leg press (LPH), and a low foot placement leg press (LPL) employing a wide stance (WS), narrow stance (NS), and two foot angle positions (feet straight and feet turned out 30°).
Results: No differences were found in muscle activity or knee forces between foot angle variations. The squat generated greater quadriceps and hamstrings activity than the LPH and LPL, the WS-LPH generated greater hamstrings activity than the NS-LPH, whereas the NS squat produced greater gastrocnemius activity than the WS squat. No ACL forces were produced for any exercise variation. Tibiofemoral (TF) compressive forces, PCL tensile forces, and patellofemoral (PF) compressive forces were generally greater in the squat than the LPH and LPL, and there were no differences in knee forces between the LPH and LPL. For all exercises, the WS generated greater PCL tensile forces than the NS, the NS produced greater TF and PF compressive forces than the WS during the LPH and LPL, whereas the WS generated greater TF and PF compressive forces than the NS during the squat. For all exercises, muscle activity and knee forces were generally greater in the knee extending phase than the knee flexing phase.
Conclusions: The greater muscle activity and knee forces in the squat compared with the LPL and LPH implies the squat may be more effective in muscle development but should be used cautiously in those with PCL and PF disorders, especially at greater knee flexion angles. Because all forces increased with knee flexion, training within the functional 0–50° range may be efficacious for those whose goal is to minimize knee forces. The lack of ACL forces implies that all exercises may be effective during ACL rehabilitation.
Key Words: POWERLIFTING, KINETICS, PATELLOFEMORAL, TIBIOFEMORAL, ACL, PCL, COMPRESSIVE, SHEAR, REHABILITATION, FORCE, MUSCLE ACTIVITY, EMG
The dynamic squat and leg press (LP) exercises are common core exercises that are utilized by athletes to enhance performance in sport. These multi-joint exercises develop the largest and most powerful muscles of the body and have biomechanical and neuromuscular similarities to many athletic movements, such as running and jumping. Because the squat and LP are considered closed kinetic chain exercises (11,34), they are often recommended and utilized in clinical environments, such as during knee rehabilitation after anterior cruciate ligament (ACL) reconstruction surgery (17,23). Athletes and rehabilitation patients perform the squat and LP exercises with varying techniques according to their training or rehabilitation protocols. An athlete or patient with patellar chondromalacia, or recovering from ACL reconstruction, may prefer a squat or LP technique that minimizes patellofemoral compressive force or tibiofemoral anterior shear force. Athletes or patients typically choose a squat or LP technique according to personal preference and effectiveness. Furthermore, athletes often use varying techniques to develop specific muscles. Some prefer training the squat and LP with a narrow stance, whereas others prefer a wide stance. Similarly, some athletes prefer their feet pointing straight ahead, whereas others prefer their feet slightly turned out. In addition, some athletes prefer a high foot placement on the LP foot plate, whereas others prefer a low foot placement. However, the effects that these varying stances, foot angles, and foot placements have on knee forces and muscle activity is currently unknown.