1. Sam Barrett
Dr. Piazza
Kines 384
Joint Moments of the Knee and Hip during High-bar and Low-bar Squatting
Introduction:
The method of inverse dynamics is often times used to estimate the mechanical effort
needed to perform a task. With the direct measurement of muscle forces being invasive and
rarely attainable, techniques involving motion analysis and equations are utilized to solve for the
net joint moment(s) of interest. The net joint moment in turn provides an estimate of the
minimum collective torque required by all of the muscles crossing the joint structure (Bryanton,
2012). The squat is one of many renowned strength training exercises and can be performed in
numerous ways depending on the intended outcome. For this reason it has been used in many
studies to develop a deeper understanding of lower body mechanics.
The purpose of this experiment was to calculate the net joint moments generated at the
hip and knee joints while performing a back squat with a barbell set in two different positions,
high-bar and low-bar, using two-dimensional motion analysis and force plates. In the high-bar
position the barbell was placed across the shoulders just under the spinous process of C7. The
low-bar position had the barbell sitting a little further down across the spine of the scapula. In
addition to comparing the forces at the hip and knee joint for the different bar positions, the
experiment addressed the differences in the ground reaction forces applied to each foot
throughout the movement. By doing this we could better understand how the force was
distributed between the legs over the duration of the squat.
After measurements of the normal forces, parallel forces, and centers of pressure during
each squat were taken, along with locating the position of the joint centers, the moments
corresponding to each joint throughout the movement were calculated and compared to see how
the different barbell positions distribute the moments between the two joint structures.

2. I hypothesized that the low-bar position would result in a greater peak joint moment in
the hip compared to that of the knee, the high-bar position would demonstrate a relatively equal
distribution of joint moments between the two joint structures, and the ground reaction forces
acting on each foot would be equal throughout the squat for both barbell positions. This is
because performing a high-bar squat tends to result in less of a forward lean demonstrated by the
trunk and upper extremities than is seen during a low-bar squat.
Methods:
The materials used during this experiment consisted of two force plates recording at 50
Hz, one video camera recording at 30 Hz, one tripod, one barbell (20.45 kg), orange Duck Tape,
MaxTRAQ motion analysis software, and PASCO Capstone software. The force plates used for
this experiment were two dimensional and were used for measuring the normal force (N),
parallel force (N), and center of pressure (m) applied to the plate by the foot. The video camera
was mounted on the tripod while recording to insure that the only movement taking place during
the experiment is from subject. The weight of the barbell alone was decided to be used for the
experiment because that is the foundation before more weight can be applied. Duck Tape served
as markers at various points of interest during video recording. PASCO Capstone software was
used to collect and analyze the data recorded from the force plate. The MaxTRAQ software was
used to analyze the squatting motion recorded by the video camera.
The experiment was performed without any footwear by one male subject age 21
weighing 74 kilograms with over a year of regular squatting experience. Before the experiment
took place the data analysis software was first set up to record normal and parallel forces as well
as the center of pressure and display those recordings in graphs and tables. The force plates were
first positioned to accommodate the subject’s squat stance. Markers were then placed on the ends

3. of the closest force plate to the video camera in the same plane as the subject’s feet as well as on
the greater trochanter of the subject’s femur, lateral tibial epichondyle of the knee, and lateral
malleolus of the ankle on the subject’s right leg.
The force plates were zeroed before the subject placed the barbell in the high-bar
position and assumed their squat stance on top of them. The camera was placed perpendicular to
the direction the subject was facing and positioned to include the force plate, hip, knee, ankle,
and foot in the frame. After video and force data recording began, the subject tapped the force
plate with their right foot, steadied themselves, and then proceeded to perform the squat until
their knee formed a minimum of a 90 angle before reversing the movement in a slow and̊
controlled manner. The tapping of the foot prior to squatting presented a common point in both
the force and video data to be utilized for synchronizing the two. After finishing the squat,
recording was ended and the subject stepped off of the force plates and removed the barbell from
their back until the next trial.
After quickly reviewing the force data for any noticeable errors the force plates were
zeroed once again and the subject placed the barbell on their back, this time in the low-bar
position, before stepping onto the plates. The subject again tapped the plate with their foot after
recording began before performing the new squatting technique at the same pace and with the
same depth restrictions. After completing the squat, video and force data recording was
concluded and the subject stepped off the plates and removed the barbell from their back.
Next, the video footage from both trials was exported to MaxTRAQ where each marker
was digitized for every frame from the moment the foot tapped the force plate until the subject
returned to their initial squat stance. This was done for both trials with a scale set for the length
of the force plate in order to calculate the moment arm (m) of the hip and knee joint coordinates

4. relative to the center of pressure. The force plate data recorded by the PASCO Capstone software
was reinterpreted for 30 Hz using a Pascal computer program to match that of the video
recording.
Joint structure coordinates from video digitization and force data for each frame were
exported to an excel spreadsheet with equations to calculate the center of mass for the foot,
shank, and thigh, normal and parallel forces for the hip and knee, and the moments for both the
hip and knee. The values for the hip and knee joint moments were calculated throughout the
squat for both the high-bar and low-bar techniques and compared.
Results:
During the high-bar session of the experiment the knee joint moment rapidly increased as
the subject lowered themselves into the squatting position until it reached a peak at 92 Nm before
decreasing briefly to 76 Nm and then establishing a second peak at 94 Nm prior to returning to it
starting value as the subject returned to the starting stance. The hip joint moment increased as
well at a slightly slower rate to a single peak of 82 Nm as the subject descended into the squat
position before decreasing back to its original value as the subject returned to the stance position.
The knee joint moment was larger than the hip joint moment for nearly the entire squat using this
bar position with the exception of a small portion of the ascending phase of the exercise before
reaching their original stance.

5. 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
-40
-20
0
20
40
60
80
100
120
MK
MH
Time (s)
Extension(+)Torque(Nm)
Figure 1: High-bar Knee vs. Hip Joint Moments
The first 0.5-0.75 seconds of the graph represent the subject attempting to restore their initial stance after tapping the
force plate with their foot. MK represents the knee joint moment and MH represents the hip joint moment.
The knee joint moment during the low-bar trend followed the same double peak pattern
as in the high-bar squat with its two peaks at 86 and 96 Nm while it decreased to 70 Nm in
between. The hip joint moment increased steadily to a peak value of 80 Nm before rapidly
decreasing to its original value as the subject ascended to their original stance position. The hip
joint moment was only slightly greater than the knee joint moment for an instant just prior to
reaching its peak value.
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
-20
0
20
40
60
80
100
120
MK
MH
Time (s)
Extension(+)Torque(Nm)
Figure 2: Low-bar Knee vs. Hip Joint Moments

6. The first 0.5 seconds of the graph represent the subject attempting to restore their initial stance after tapping the
force plate with their foot. MK represents the knee joint moment and MH represents the hip joint moment.
When compared with one another, the knee joint moment for the high-bar had two peaks
at 92 and 94 Nm with a decrease in value to 76 Nm in between and the low-bar knee joint
moment also had two peaks with values at 86 and 96 Nm while decreasing to a value of 70 Nm
in between.
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
-20
0
20
40
60
80
100
120
MKH
MKL
Time (s)
KneeExtention(+)Torque(Nm)
Figure 3: High-bar vs. Low-bar Knee Joint Moments
Hip joint moments for high-bar and low-bar position increased to values of 82 and 80 Nm
respectively before decreasing back to the initial stance values.
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
-20
0
20
40
60
80
100
MHH
MHL
Time (s)
HipExtension(+)Torque(Nm)
Figure 4: High-bar vs. Low-bar Hip Joint Moments

7. Forces applied to each foot during the high-bar squat were relatively equal throughout
with values fluctuating between 400 and 600 N while the squat was being performed and
between 400 and 500 N while the subject was standing still. During the low-bar squat the
fluctuations fell within the same ranges but the forces applied to each foot were not as close to
each other throughout the movement.
0 1 2 3 4 5 6 7 8
0
100
200
300
400
500
600
700
800
900
RFF
LFF
Time (s)
Force(N)
0 1 2 3 4 5 6 7
0
100
200
300
400
500
600
700
800
900
1000
RFF
LFF
Time (s)
Force(N)
Figures 5 and 6: High-bar (left) and Low-bar (right) Ground Reaction Forces Applied to the Right and
Left Foot*
*RFF represents the ground reaction force applied to the right foot and the LFF represents the ground reaction force
applied to the left foot.
Discussion:
Based on the results of the experiment the knee joint moment was slightly larger than the
hip joint moment for both the high-bar and low-bar position but overall the forces were nearly
equally distributed between the two joint structures. This outcome did support my hypothesis of
the joint moments being equal during the high-bar squat but did not support my hypothesis of the
hip joint producing a greater moment than knee joint under the low-bar condition.
A previous study regarding high-bar and low-bar technique used a load of 65% of each
lifter’s 1 repetition maximum and concluded that using the low-bar technique demonstrated a
more prominent forward trunk lean which lead to a larger hip joint moment; whereas using the

8. high-bar technique more equally distributes the load between the joints (Wretenberg, 1996). The
reason for this is that the high-bar position requires less compensation to reposition the center of
mass of the subject with the barbell over the center of pressure for the ground reaction force
throughout the movement. It is this difference in technique that alters the position of the joints
relative to the center of pressure and ultimately the moments generated at each joint throughout
the movement. The same conclusion of a more prominent anterior trunk lean resulting in
additional forces being transferred to the hip and low back region producing a larger hip joint
moment was drawn from a study concerning the effect of knee position on hip and knee torques
during the barbell squat (Fry, 2003). Another study found that the back squat exercise required a
large mechanical effort from the knee and hip extensor muscles and that the effort from both
groups increased as the barbell load increased. However, the hip extensor moment increased to a
greater extent than the knee extensor moment as the barbell load increased (Bryanton, 2012).
The values for the hip and knee joint moment between both bar positions for this
experiment turned out to be nearly identical. This was likely caused by the lack of a sufficient
loading to provoke any differences in technique from revealing themselves during the lift as
suggested by Wretenberg and Bryanton. The barbell alone was not heavy enough to require any
additional compensation from the hip joint.
The ground reaction forces between the left and right foot were very well distributed
throughout the high-bar squat. Much more so than the low-bar squat. This outcome strongly
supported my hypothesis of an equal distribution between each leg for the high-bar position and
weakly supported my hypothesis of an equal distribution for the low-bar position. The average
difference in the ground reaction force applied to each foot during the high-bar squat was only 5
N while during the low-bar squat the average difference was 24 N.

9. Future considerations for this experiment would include the use of more subjects and a
more substantial barbell load. A minimum of two subjects, preferably more, would allow for
comparison and confirmation of consistency, or lack there of, between subject results. Also, a
barbell load equal to the subjects’ bodyweight should provide a sufficient and consistent load
between subjects for a more accurate result concerning differences between the techniques (Fry,
2003).
References
Bryanton, Megan A. (2012). "EFFECT OF SQUAT DEPTH AND BARBELL LOAD ON
RELATIVE MUSCULAR EFFORT IN SQUATTING". Journal of strength and conditioning
research (1064-8011), 26 (10), p. 2820.
Fry, Andrew C (11/2003). "Effect of knee position on hip and knee torques during the barbell
squat". Journal of strength and conditioning research (1064-8011), 17 (4), p. 629.
Wretenberg, P (02/1996). "High- and low-bar squatting techniques during weight-training".
Medicine and science in sports and exercise (0195-9131), 28 (2), p. 218. doi:
10.1097/00005768-199602000-00010

10. Future considerations for this experiment would include the use of more subjects and a
more substantial barbell load. A minimum of two subjects, preferably more, would allow for
comparison and confirmation of consistency, or lack there of, between subject results. Also, a
barbell load equal to the subjects’ bodyweight should provide a sufficient and consistent load
between subjects for a more accurate result concerning differences between the techniques (Fry,
2003).
References
Bryanton, Megan A. (2012). "EFFECT OF SQUAT DEPTH AND BARBELL LOAD ON
RELATIVE MUSCULAR EFFORT IN SQUATTING". Journal of strength and conditioning
research (1064-8011), 26 (10), p. 2820.
Fry, Andrew C (11/2003). "Effect of knee position on hip and knee torques during the barbell
squat". Journal of strength and conditioning research (1064-8011), 17 (4), p. 629.
Wretenberg, P (02/1996). "High- and low-bar squatting techniques during weight-training".
Medicine and science in sports and exercise (0195-9131), 28 (2), p. 218. doi:
10.1097/00005768-199602000-00010