Effects of technique variations on knee biomechanics during the squat and leg press. Abstract:
ESCAMILLA, R. F., G. S. FLEISIG, N. ZHENG, J. E. LANDER, S. W. BARRENTINE, J. R. ANDREWS, B. W. BERGEMANN, and C. T. MOORMAN, III. 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[degrees]).
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[degrees] 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.
(C) 2001 Lippincott Williams & Wilkins, Inc.
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An EMG Comparison Study of a Leg Press and a Squat Lift Melissa James MPT, Heidi Ivesdal, Thomas Mohr PT, PhD, John Frappier MS
Dept. of Physical Therapy, University of North Dakota, Grand Forks, ND
Abstract: Purpose. The purpose of this study was to compare muscle recruitment during a leg press and a traditional squat lift. Subjects. Two groups of subjects were used for this study. Group 1 consisted of ten, healthy, normal males. Group 2 consisted of sixteen, healthy, trained, male athletes. Methods. Surface electromyographic (EMG) activity was recorded from the erector spinae (ES), gluteus maximus (GM), vastus lateralis (VL), and biceps femoris (BF) muscles. The exercises performed were a leg press (Plyo-Press), and a traditional squat lift. Each subject in Group 1 performed three repetitions of each exercise using a weight equivalent to their body weight (155 to 265 lbs). Each subject in Group 2 performed three repetitions of each exercise using a weight equivalent to 80% of their 1 RM (225 to 600 lbs). Results. In the trained group (Group 2), the squat exercise elicited significantly more EMG activity than did the leg press in the ES, GM and BF. There was no significant difference in the VL activity between the two exercises. In the normal group (Group 1), the results were similar in that the squat exercise also elicited significantly more EMG activity in the ES, GM and BF. In the normal group there was no significant difference in the VL activity between the two exercises. Conclusion. In this study, the leg press provided the same level of muscle recruitment in the VL as did the squat exercise. However, the leg press did not recruit the ES, GM or BF to the extent that the squat exercise did. Therefore, we hypothesize that the leg press machine may be better for individuals who want to specifically strengthen their quadriceps musculature, but reduce the strain on the low back that may be caused by the excessive activity of the ES musculature.
Purpose: It has been suggested that traditional squat lifting with free weights may put strain on the low back because of the increased muscle activity in the low back musculature that occurs during the lift. Furthermore, it has been proposed that the leg press will activate the quadriceps muscles to the same extent as the squat lift without excessive activation of the low back musculature. However, there is little research to support these claims. Therefore, the purpose of this study was to compare muscle recruitment during a leg press and a traditional squat lift. It has been suggested that traditional squat lifting with free weights may put strain on the low back because of the increased muscle activity in the low back musculature that occurs during the lift.
Furthermore, it has been proposed that the leg press will activate the quadriceps muscles to the same extent as the squat lift without excessive activation of the low back musculature. However, there is little research to support these claims. Therefore, the purpose of this study was to compare muscle recruitment during a leg press and a traditional squat lift.
Methods: Subjects. Two groups of subjects were used for this study. Group 1 consisted of ten, healthy, normal males. Group 2 consisted of sixteen, healthy, trained, male athletes. The subjects in Group 1 were chosen because they were able to squat lift a weight equivalent to 75% of their body weight. The subjects in Group 2 were chosen because they were able to squat lift a weight equivalent to 80% of their 1 RM.
Instrumentation. The EMG data was recorded using the Noraxon Telemyo8 transmitter/receiver and analyzed using the MyoSoft software package.
Procedure. Surface electromyographic (EMG) activity was recorded from the erector spinae (ES), gluteus maximus (GM), vastus lateralis (VL), and biceps femoris (BF) muscles. The exercises performed were: 1) a leg press using the Plyo-Press® device, and 2) a traditional squat lift using free weights. Each subject in Group 1 performed three repetitions of each exercise using a weight equivalent to their body weight (155 to 265 lbs). Each subject in Group 2 performed three repetitions of each exercise using a weight equivalent to 80% of their 1 RM (225 to 600 lbs).
Data Analysis. The EMG activity was normalized based on a maximal voluntary contraction (MVC) for each muscle. A comparison was made of the normalized EMG values, recorded for each muscle, during the two exercises using paired t-tests. Alpha levels of 0.05 were used to test for significance.
Figure 1. Subject on the PlyPress
Results: In the trained group (Group 2), the squat exercise elicited significantly more EMG activity than did the leg press in the ES, GM and BF. However, there was no significant difference in the VL activity between the two exercises (Table 1). In the normal group (Group 1), the results were similar in that the squat exercise also elicited significantly more EMG activity in the ES, GM and BF (Table 2). As with the trained group, there was no significant difference in the VL activity between the two exercises.
Figure 2. PlyoPress versus squat exercise
Figure 3. Leg press versus squat exercise.
CONCLUSION: The leg press provides the same level of muscle recruitment in the VL as does a squat exercise. However, the leg press does not recruit the ES, GM or BF to the extent that the squat exercise does. Therefore, we hypothesize that the leg press machine may be better for individuals who want to specifically strengthen their quadriceps musculature, but reduce possible strain on the low back that may be caused by the excessive activity of the ES musculature. However, if the training is aimed at training the ES, GM or BF; then the squat lift may provide a better training stimulus.