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Here is some interesting research which examines knee kinematics and compares
the various forces produced in the knee joint by exercises such as squats,
leg presses and knee extensions.
Note in the first two articles that the old therapeutic favourite, knee
extensions, stresses the ACL (anterior cruciate ligament), whereas the squat
and leg press do not (note in the last article that this relates to the type
of squat being used). The compressive force between femur and tibia is also
greatest during knee extensions. Note, however, that PCL (posterior cruciate
ligament) is exposed to about twice the force during the squat compared with
knee extensions. No doubt these findings will be of interest to therapists
on this list. One clear message is that knee extensions should be avoided as
a primary method of ACL rehabilitation.
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Zheng N, Fleisig GS, Escamilla RF, Barrentine SW
An analytical model of the knee for estimation of internal forces during
exercise. J Biomech 1998 Oct; 31(10): 963-7
An analytical model of the knee joint was developed to estimate the forces at
the knee during exercise. Muscle forces were estimated based upon
electromyographic activities during exercise and during maximum voluntary
isometric contraction (MVIC), physiological cross-sectional area (PCSA),
muscle fiber length at contraction and the maximum force produced by an unit
PCSA under MVIC. Tibiofemoral compressive force and cruciate ligaments'
tension were determined by using resultant force and torque at the knee,
muscle forces, and orientations and moment arms of the muscles and ligaments.
An optimization program was used to minimize the errors caused by the
estimation of the muscle forces. The model was used in a ten-subject study of
open kinetic chain exercise (seated knee extension) and closed kinetic chain
exercises (leg press and squat). Results calculated with this model were
compared to those from a previous study which did not consider muscle length
and optimization.
Peak tibiofemoral compressive forces were:
3285 ± 1927 N during knee extension.
3155 ±755 N during leg press
3134 ± 1040 N during squat
Peak posterior cruciate ligament tensions were:
1868 ± 878 N during squat,
1866 ± 383 N during leg press
959 ± 300 N for seated knee extension.
No significant anterior cruciate ligament (ACL) tension was found during leg
press and squat.
Peak ACL tension was 142 ±257 N during seated knee extension.
It is demonstrated that the current model provided better estimation of knee
forces during exercises, by preventing significant overestimates of
tibiofemoral compressive forces and cruciate ligament tensions. >
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Escamilla RF, Fleisig GS, Zheng N et al
Biomechanics of the knee during closed kinetic chain and open kinetic chain
exercises. Med Sci Sports Exerc 1998 Apr; 30(4):556-69
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 (Open Chain)
when the knee was near full extension. OKCE (Open Chain) produced more rectus
femoris activity while CKCE (Closed Chain) 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 (Closed Chain) ,
and increased with knee flexion. Tension in the anterior cruciate ligament
was present only in OKCE (Open Chain), 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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Escamilla RF, Fleisig G S et al
Effects of technique variations on knee biomechanics during the squat and leg
press. Med Sci Sports Exerc 2001 Sep; 33(9):1552-66
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.
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Stuart MJ, Meglan DA, Lutz GE, Growney ES, An KN
Comparison of intersegmental tibiofemoral joint forces and muscle activity
during various closed kinetic chain exercises. Am J Sports Med 1996
Nov-Dec;24(6):792-9
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 the
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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Escamilla RF
Knee biomechanics of the dynamic squat exercise Med Sci Sports Exerc 2001
Jan;33(1):127-41
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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Lutz GE, Palmitier RA, An KN, Chao EY
Comparison of tibiofemoral joint forces during open-kinetic-chain and
closed-kinetic-chain exercises J Bone Joint Surg Am 1993 May; 75(5):732-9
The purpose of this study was to analyze forces at the tibiofemoral joint
during open and closed-kinetic-chain exercises. Five healthy subjects
performed maximum isometric contractions at 30, 60, and 90 degrees of knee
flexion during open-kinetic-chain extension, open-kinetic-chain flexion, and
closed-kinetic-chain exercises. Electromyographic activity of the quadriceps
and hamstrings, as well as load and torque-cell data, were recorded.
Tibiofemoral shear and compression forces were calculated with use of a
two-dimensional biomechanical model.
The results showed that, during the open-kinetic-chain extension exercise,
maximum posterior shear forces (the resisting forces to anterior drawer) of
285 ± 120 newtons (mean and standard deviation) occurred at 30 degrees of
knee flexion and maximum anterior shear forces (the resisting forces to
posterior drawer) of 1780 ± 699 newtons occurred at 90 degrees of knee
flexion.
The closed-kinetic-chain exercise produced significantly less posterior shear
force at all angles when compared with the open-kinetic-chain extension
exercise. In addition, the closed-kinetic-chain exercise produced
significantly less anterior shear force at all angles except 30 degrees when
compared with the open-kinetic-chain flexion exercise. Analysis of
tibiofemoral compression forces and electromyographic recruitment patterns
revealed that the closed-kinetic-chain exercise produced significantly
greater compression forces and increased muscular co-contraction at the same
angles at which the open-kinetic-chain exercises produced maximum shear
forces and minimum muscular co-contraction.
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Toutoungi DE, Lu TW, Leardini A, Catani F, O'Connor JJ.
Cruciate ligament forces in the human knee during rehabilitation exercises.
Clin Biomech (Bristol, Avon) 2000 Mar; 15(3): 176-87
OBJECTIVE: To determine the cruciate ligament forces occurring during typical
rehabilitation exercises.Design. A combination of non-invasive measurements
with mathematical modelling of the lower limb.Background. Direct measurement
of ligament forces has not yet been successful in vivo in humans. A promising
alternative is to calculate the forces mathematically.
METHODS: Sixteen subjects performed isometric and isokinetic or squat
exercises while the external forces and limb kinematics were measured.
Internal forces were calculated using a geometrical model of the lower limb
and the "dynamically determinate one-sided constraint" analysis procedure.
RESULTS: During isokinetic/isometric extension, peak anterior cruciate
ligament forces, occurring at knee angles of 35-40 degrees, may reach 0.55x
body-weight. Peak posterior cruciate ligament forces are lower and occur
around 90 degrees. During isokinetic/isometric flexion, peak posterior
cruciate forces, which occur around 90 degrees, may exceed 4x body-weight;
the anterior cruciate is not loaded. During squats, the anterior cruciate is
lightly loaded at knee angles up to 50 degrees, after which the posterior
cruciate is loaded. Peak posterior cruciate forces occur near the lowest
point of the squat and may reach 3.5x body-weight.
CONCLUSIONS: For anterior cruciate injuries, squats should be safer than
isokinetic or isometric extension for quadriceps strengthening, though
isokinetic or isometric flexion may safely be used for hamstrings
strengthening. For posterior cruciate injuries, isokinetic extension at knee
angles less than 70 degrees should be safe but isokinetic flexion and deep
squats should be avoided until healing is well-advanced.
RELEVANCE: Good rehabilitation is vital for a successful outcome to cruciate
ligament injuries. Knowledge of ligament forces can aid the physician in the
design of improved rehabilitation protocols.
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The following study showed that closed chain exercise (the squat) produces
far greater improvement in "functional" strength and jumping ability than
open chain exercise (knee extension). Even though tests showed significant
improvements in isotonic strength, this strength did not transfer to the
isokinetic knee extension, confirming what we already know, namely that
strength training tends to be very specific. Yet, there are still those who
doggedly avoid the squat and maintain that knee extension and similar types
of machine training are just as good for sporting function.
Augustsson J, Esko A, Thomee R, Svantesson U
Weight training of the thigh muscles using closed vs. open kinetic chain
exercises: a comparison of performance enhancement J Orthop Sports Phys
Ther 1998 Jan; 27(1):3-8
Dept of Rehabilitation Medicine, Goteborg University, Sweden.
Resistance training is commonly used in sports for prevention of injuries and
in rehabilitation. The purpose of this study was to compare closed vs. open
kinetic chain weight training of the thigh muscles and to determine which
mode resulted in the greatest performance enhancement.
Twenty-four healthy subjects were randomized into a barbell squat or a knee
extension and hip adduction variable resistance weight machine group and
performed maximal, progressive weight training twice a week for 6 weeks. All
subjects were tested prior to training and at the completion of the training
period. A barbell squat 3-repetition maximum, an isokinetic knee extension
1-repetition maximum, and a vertical jump test were used to monitor effects
of training. Significant improvements were seen in both groups in the barbell
squat 3-repetition maximum test.
The closed kinetic chain group improved 23 kg (31%), which was significantly
more than the 12 kg (13%) seen in the open kinetic chain group. In the
vertical jump test, the closed kinetic chain group improved significantly, 5
cm (10%), while no significant changes were seen in the open kinetic chain
group.
A large increase of training load was observed in both subject groups;
however, improvements in isotonic strength did not transfer to the isokinetic
knee extension test. The results may be explained by neural adaptation,
weight training mode, and specificity of tests.
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This study also concluded that closed kinetic chain training appears to be
more effective than joint isolation exercise in restoring function in
patients with patellofemoral pain and dysfunction.
Stiene HA, Brosky T, Reinking MF, Nyland J, Mason MB.
A comparison of closed kinetic chain and isokinetic joint isolation exercise
in patients with patellofemoral dysfunction. J Orthop Sports Phys Ther 1996
Sep;24(3):136-41
Recently, there has been attention to the clinical application of closed
kinetic chain and joint isolation exercise. Our purpose was to compare the
effect of joint isolation and closed kinetic chain exercise on quadriceps
muscle performance and perceived function in patients with patellofemoral
pain. Twenty-three patients participated in an 8-week training period and
were assigned to either a closed kinetic chain or a joint isolation exercise
training group. An 8-inch (20.3 cm) retro step-up test was performed at
baseline, 8 weeks, and 1 year. Seated knee extension testing was measured at
baseline and at 8 weeks using peak concentric torque on an isokinetic
dynamometer at 90 degs/sec, 180 degs/sec, and 360 degs/sec. Perceived
functional status was rated as excellent, good, fair, or poor based on
questionnaire response.
Statistical analysis showed that both groups had significant improvement in
peak torque at all speeds, but only the closed kinetic chain group showed
significant improvement in closed kinetic chain testing and perceived
functional status. We concluded that closed kinetic chain training may be
more effective than joint isolation exercise in restoring function in
patients with patellofemoral dysfunction.
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The findings in the following study demonstrate that maximum knee motion may
not necessarily correspond to the highest forces in the ACL. They also
suggest that hamstring co-contraction with quadriceps is effective in
reducing excessive forces in the ACL especially between 15-60 degs of knee
flexion. This would appear to show that the powerlifting style of squatting
with butt pushed strongly backwards, with glutes and hamstrings strongly
involved, decreases force in the ACL. This has two implications - the
powerlifting squat tends to protect the ACL, but decreases the conditioning
effect on the ACL. The weighlifting "deep knee bend" type of squat may then
offer a superior method of conditioning the ACL, suggesting that powerlifters
or athletes who wish to strengthen their ACLs should periodically include
full weightlifting squats in their routines.
Li G, Rudy TW, Sakane M, Kanamori A, Ma CB, Woo SL
The importance of quadriceps and hamstring muscle loading on knee kinematics
and in-situ forces in the ACL
J Biomech 1999 Apr;32(4):395-400
This study investigated the effect of hamstring co-contraction with
quadriceps on the kinematics of the human knee joint and the in-situ forces
in the anterior cruciate ligament (ACL) during a simulated isometric
extension motion of the knee. Cadaveric human knee specimens (n = 10) were
tested using the robotic universal force moment sensor (UFS) system and
measurements of knee kinematics and in-situ forces in the ACL were based on
reference positions on the path of passive flexion/extension motion of the
knee.
With an isolated 200 N quadriceps load, the knee underwent anterior and
lateral tibial translation as well as internal tibial rotation with respect
to the femur. Both translation and rotation increased when the knee was
flexed from full extension to 30 degs of flexion; with further flexion, these
motion decreased.
The addition of 80 N antagonistic hamstrings load significantly reduced both
anterior and lateral tibial translation as well as internal tibial rotation
at knee flexion angles tested except at full extension. At 30 degs of
flexion, the anterior tibial translation, lateral tibial translation, and
internal tibial rotation were significantly reduced by 18, 46, and 30%,
respectively. The in-situ forces in the ACL under the quadriceps load were
found to increase from 27.8 ± 9.3 N at full extension to a maximum of 44.9 ±
13.8 N at 15 deg of flexion and then decrease to 10 N beyond 60 deg of
flexion. The in-situ force at 15 degs was significantly higher than that at
other flexion angles.
The addition of the hamstring load of 80 N significantly reduced the in-situ
forces in the ACL at 15, 30 and 60 degs of flexion by 30, 43, and 44%,
respectively. These data demonstrate that maximum knee motion may not
necessarily correspond to the highest in-situ forces in the ACL. The data
also suggest that hamstring co-contraction with quadriceps is effective in
reducing excessive forces in the ACL particularly between 15 and 60 degs of
knee flexion.
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Dr Mel C Siff
Denver, USA
http://groups.yahoo.com/group/Supertraining/
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