For anyone who doubts the conditioning value and safety of the squat, read
the following research studies which relate to the the use of the squat in
knee rehabilitation:
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Med Sci Sports Exerc 2001 Jan;33(1):127-41
Knee biomechanics of the dynamic squat exercise.
Escamilla RF.
PURPOSE: Because a strong and stable knee is paramount to an 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 60
degrees 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 between 0 and 50
degrees 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 degrees 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
ligaments may 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.
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Med Sci Sports Exerc 1989 Jun;21(3):299-303
The effect of the squat exercise on knee stability.
Chandler TJ, Wilson GD, Stone MH.
Past studies have produced conflicting results as to the effect of squat
exercises on knee stability. One hundred male and female college students
were measured using a knee ligament arthrometer on nine tests of knee
stability. Over an 8-wk training program, full or half squats did not
consistently affect knee stability compared to non-squatting controls. To
measure the effect of long-term squat training 27 male powerlifters (14 Elite
or Master Class) and 28 male weightlifters (8 Elite or Master Class) were
measured on the same tests.
Powerlifters were significantly tighter than controls on the anterior drawer
at 90 degrees of knee flexion. Both powerlifters and weightlifters were
significantly tighter than controls on the quadriceps active drawer at 90
degrees of knee flexion. Data on powerlifters and weightlifters were also
analyzed by years of experience and skill level. No effect of squat training
on knee stability was demonstrated in any of the groups tested.
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Med Sci Sports Exerc 1998 Apr;30(4):556-69
Biomechanics of the knee during closed kinetic chain and open kinetic chain
exercises.
Escamilla RF, Fleisig GS, Zheng N, Barrentine SW, Wilk KE, Andrews JR.
PURPOSE: Although closed (CKCE) and open (OKCE) kinetic chain exercises are
used in athletic training and clinical environments, few studies have
compared knee joint biomechanics while these exercises are performed
dynamically. The purpose of this study was to quantify knee forces and muscle
activity in CKCE (squat and leg press) and OKCE (knee extension).
METHODS: Ten male subjects performed three repetitions of each exercise at
their 12-repetition maximum. Kinematic, kinetic, and electromyographic data
were calculated using video cameras (60 Hz), force transducers (960 Hz), and
EMG (960 Hz). Mathematical muscle modeling and optimization techniques were
employed to estimate internal muscle forces.
RESULTS: Overall, the squat generated approximately twice as much hamstring
activity as the leg press and knee extensions. Quadriceps muscle activity was
greatest in CKCE when the knee was near full flexion and in OKCE when the
knee was near full extension. OKCE produced more rectus femoris activity
while CKCE produced more vasti muscle activity. Tibiofemoral compressive
force was greatest in CKCE near full flexion and in OKCE near full
extension. Peak tension in the posterior cruciate ligament was approximately
twice as great in CKCE, and increased with knee flexion. Tension in the
anterior cruciate ligament was present only in OKCE, and occurred near full
extension. Patellofemoral compressive force was greatest in CKCE near full
flexion and in the mid-range of the knee extending phase in OKCE.
CONCLUSION: An understanding of these results can help in choosing
appropriate exercises for rehabilitation and training.
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Clin Biomech (Bristol, Avon) 2001 Jun;16(5):424-30
Patellofemoral joint kinetics during squatting in collegiate women athletes.
Salem GJ, Powers CM.
OBJECTIVE:To characterize the biomechanics of the patellofemoral joint during
squatting in collegiate women athletes.
DESIGN: Repeated measures experimental design. BACKGROUND: Although squatting
exercises are required components of most intercollegiate
resistance-training programs and are commonly performed during
rehabilitation, the effects of various squatting depths on patellofemoral
joint stress have not been quantified.
METHODS: Anthropometric data, three-dimensional knee kinematics, and ground
reaction forces were used to calculate the knee extensor moment (inverse
dynamics approach) in five intercollegiate female athletes during squatting
exercise at three different depths (approximately 70 degrees, 90 degrees and
110 degrees of knee flexion). A biomechanical model of the patellofemoral
joint was used to quantify the patellofemoral joint reaction force and
patellofemoral joint stress during each trial.
RESULTS: Peak knee extensor moment, patellofemoral joint reaction force and
patellofemoral joint stress did not vary significantly between the three
squatting trials.
CONCLUSIONS: Squatting from 70 degrees to 110 degrees of knee flexion had
little effect on patellofemoral joint kinetics. The relative constancy of
the patellofemoral joint reaction force and joint stress appeared to be
related to a consistent knee extensor moment produced across the three
squatting depths.
RELEVANCE: The results of this study do not support the premise that
squatting to 110 degrees places greater stress on the patellofemoral joint
than squatting to 70 degrees. These findings may have implications with
respect to the safe design of athletic training regimens and rehabilitation
programs.
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J Orthop Sports Phys Ther 2002 Apr;32(4):141-
Patellofemoral joint kinetics while squatting with and without an external
load.
Wallace DA, Salem GJ, Salinas R, Powers CM.
STUDY DESIGN: Single-group repeated measures design. OBJECTIVE: To quantify
patellofemoral joint reaction forces and stress while squatting with and
without an external load.
BACKGROUND: Although squatting exercises in the rehabilitation setting are
often executed to a relatively shallow depth in order to avoid the higher
joint forces associated with increased knee flexion, objective criteria for
ranges of motion have not been established. Methods and Measures: Fifteen
healthy adults performed single-repetition squats to 90 degrees of knee
flexion without an external load and with an external load (35% of the
subject's body weight [BW]). Anthropometric data, three-dimensional
kinematics, and ground reaction forces were used to calculate knee extensor
moments (inverse dynamics approach), while a biomechanical model of the
patellofemoral joint was used to quantify the patellofemoral joint reaction
forces and patellofemoral joint stress. Data were analyzed during the
eccentric (0-90 degrees) and concentric (90-0 degrees phases of the squat
maneuver.
RESULTS: In both conditions, knee extensor moments, patellofemoral joint
reaction forces, and patellofemoral joint stress increased significantly
with greater knee flexion angles. Peak patellofemoral joint force and stress
was observed at 90 degrees of knee flexion. Patellofemoral joint stress at 45
degrees, 60 degrees, 75 degrees, and 90 degrees of knee flexion during the
eccentric phase, and at 75 degrees and 90 degrees during the concentric
phase, was significantly greater in the loaded trials versus the unloaded
trials.
CONCLUSION: The data indicate that during squatting, patellofemoral joint
stress increases as the knee flexion angle increases, and that the addition
of external resistance further increases patellofemoral joint stress. These
findings suggest that in order to limit patellofemoral joint stress during
squatting activities, clinicians should consider limiting terminal joint
flexion angles and resistance loads.
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Dr Mel C Siff
Denver, USA
http://groups.yahoo.com/group/Supertraining/
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