Download kinematic analysis of the powerlifting style squat and the

KINEMATIC ANALYSIS OF THE POWERLIFTING STYLE
SQUAT AND THE CONVENTIONAL DEADLIFT DURING
COMPETITION: IS THERE A CROSS-OVER EFFECT
BETWEEN LIFTS?
MICHAEL E. HALES,1 BENJAMIN F. JOHNSON,1
1
2
AND
JEFF T. JOHNSON2
Department of Health, Physical Education and Sport Science, Kennesaw State University, Kennesaw, Georgia; and
Department of Physical Education and Recreation, University of West Georgia, Carrollton, Georgia
ABSTRACT
Hales, ME, Johnson, BF, and Johnson, JT. Kinematic analysis
of the powerlifting style squat and the conventional deadlift
during competition: is there a cross-over effect between lifts?
J Strength Cond Res 23(9): 2574–2580, 2009—Many
individuals involved in the sport of powerlifting believe that
the squat and deadlift have such similar lifting characteristics
that the lifts yield comparable training results. The aim of this
study was to compare and contrast biomechanical parameters
between the conventional style deadlift and the back squat
performed by 25 lifters competing in regional powerlifting
championship. The 3-dimensional analysis incorporated 4 60
Hz synchronized video cameras for collecting data from 25
participants. Parameters were quantified at the sticking point
specific to each lift. Kinematic variables were calculated at the
hip, knee, and ankle. Paired (samples) t-tests were used to
detect significant differences in the kinematic mean scores for
the different lift types. The statistical analysis revealed
significant differences exist between the squat (0.09 m/s)
and the deadlift (0.20 m/s) vertical bar velocities. Differences
were found for angular position of the hip, knee, and ankle
between lifts. The sticking point thigh angles were quantified as
32.54 6 3.02 and 57.42 6 4.57 for the squat and deadlift,
respectively. Trunk angles were 40.58 6 6.29 (squat) and
58.30 6 7.15 (deadlift). The results indicate the back squat
represents a synergistic or simultaneous movement, whereas
the deadlift demonstrates a sequential or segmented movement. The kinematic analysis of the squat and the conventional
deadlift indicate that the individual lifts are markedly different
Address correspondence to Michael Hales, [email protected].
23(9)/2574–2580
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(p , 0.01), implying that no direct or specific cross-over effect
exists between the individual lifts.
K EY W ORDS biomechanics, sticking point, sequential,
synergistic, partial deadlift
INTRODUCTION
S
urprisingly, the controversy of whether deadlifts
should be substituted with squat exercises during
training continues to resonate throughout the
powerlifting community. Many individuals involved in the sport of powerlifting believe that the squat
and deadlift have such similar lifting characteristics that
the lifts will yield comparable training results, with a crossover effect. Numerous coaches and competitors mistakenly
continue to substitute various squat exercises into their
training programs in place of the deadlift in hopes of
miraculous performance improvements in the deadlift.
However, the resemblance appears to be primarily restricted
to submaximal deadlift loads typically used during the early
stages of a training program (10). Even though the squat and
deadlift appear similar from a simplistic mechanical standpoint, the lifts are considered quite different when analyzed
under maximal loading conditions, as used in powerlifting
competitions. It is extremely difficult for an individual to
identify the minute movement pattern differences visually,
but it is very easy to isolate variations using sophisticated
motion analysis instrumentation. From a biomechanical
perspective, the squat and deadlift are much more different
from one another than currently believed by many in the
powerlifting community.
Two basic strategies exist for lifting weights off of the
ground (i.e., the deadlift) (9). One strategy is referred to as the
leg-lift, which displays a flexed knee position with a relatively
vertical trunk position. The method demonstrates a movement that exhibits simultaneous and relatively equal angular
changes about the hip, knee, and ankle that closely resembles
the back squat movement. Conversely, the back-lift strategy
exhibits an extended knee and flexed trunk position during
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the initial phase of the movement, indicating a significantly
increased rate of knee extension. The knee movement coupled with heavy weight lifting
causes the hips to rise rapidly,
thus creating an increase in
trunk lean. The leg-lift method
demonstrates a reduced load
on the lumbar spine, which is
considered safer, but the knees
are heavily loaded, whereas the
back-lift style subjects the lumbar region to extremely high
Figure 1. Vertical bar velocity (squat).
resultant forces and moments.
Depending on the lifting strategy, lower-extremity muscle
groups are recruited in either a synergistic (leg-lift) or
deadlift styles (3,4,8) to determine which method is best
sequential (back-lift) manner to generate the necessary
for strength development or lower-extremity rehabilitation
muscle moments. Bejjani et al. (2) reported that the leg-lift
(8,21), but a comparative analysis between lift types has never
method approaches the straight leg technique when lifting
been reported. Investigating the kinematics of both lift types
extremely heavy weights caused, in part, by biomechanical
concurrently while performed by a common subject pool
constraints and the inability to maintain lumbar lordosis.
could produce information that may challenge current
During heavy weight lifting, the leg-lift method does not
training philosophies.
appear to be the preferred strategy and may not be even
METHODS
possible (18–20). In summary, no one tends to use one
method explicitly, but rather people use a combination of the
Experimental Approach to the Problem
2 different styles. However, when an individuals near their
The objective of the study was to compare the back squat and
maximal deadlift capacity, the back-lift strategy appears to be
the conventional style deadlift to determine whether a biothe most commonly used technique.
mechanical relationship exists between the individual lift
To perform a comparative analysis, a common phenomtypes. A competition setting was selected over a laboratoryenon specific to each of the individual lift types was needed to
based analysis because of the different lifting strategies used,
serve as a marker for distinguishing differences between the
submaximal versus maximal loads. An all-out effort in
lifts. The event, described as the ‘‘sticking point,’’ was selected
competition as lifters attempt to set personal or state/national
because it has been reported to occur in various weight lifting
records is very difficult to replicate in a laboratory. For this
movements, including the back squat and the deadlift
reason, a competition environment was deemed best for
(6,15,16). The sticking point of a movement is where the
addressing the issue of training specificity in relation to the
upward momentum of the barbell is momentarily decreased
squat and deadlift cross-over effect.
or stopped. This event is particularly important because the
success in weight lifting depends on a continuous motion
of the barbell past this region of
the lift. By isolating the sticking
point and identifying the biomechanical constraints associated with this region, one could
provide training implications that
address lifting technique and the
possible implementation of specific assistance-type exercises.
Numerous weight lifting
analyses have focused on
different squat techniques
Figure 2. Vertical bar velocity (Deadlift).
(1,5,7,12,14)
or
different
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The conventional style deadlift was selected for 2 reasons: a)
TABLE 1. Vertical bar velocity.
fewer lifters use the sumo style
deadlift in competition (small
Lift type
Velocity (m!s21)
subject pool), and b) the maSquat
0.10 6 0.05*
0.34 6 0.06
0.22 6 0.04
jority of the sumo style deadDeadlift
0.20 6 0.06*
0.32 6 0.04
0.24 6 0.06
lifters do not perform the
Position 1 (begin
Position 2 (peak bar
Position 3 (sticking
back squat with a wide stance,
ascent)
velocity)
point)
so the significantly different
*Significance (p , 0.01).
foot placement would affect
the biomechanical comparison.
Only lifters that used a conventional-style deadlift and relabarbell was assumed to be fixed at the shoulder during
tively narrow squat stance, heels approximately shoulder
the squat, so the shoulder joint markers were used to quantify
width, were selected for analysis. Similar foot placement was
bar motion. Contrary with previous studies, the barbell end
an important control factor for comparing the individual lift
was not selected as a point for analysis because bar flex
types.
(oscillation) occurs throughout the execution of the lifts.
Subjects
Three stages were identified during the deadlift: a) lift-off
The 25 male participants were competitors in a regional
(LO); 2) knee passing (KP); and 3) lift completion (LC). In
powerlifting contest, which also served as a national qualifier.
accordance with the United States Powerlifting Federation
The competition attracted lifters with varying skill levels,
(USPF) guidelines, the competitors were allowed 3 lift
which provided a heterogeneous group of participants. Only
attempts for each of the individual lifts (11). The maximal
lifters who successfully completed a squat and deadlift were
load successfully lifted, for each lift type, was selected for
randomly selected for analysis at the conclusion of the
analysis of each of the lifters.
contest. Before competition, body weight (93.63 6 30.9 kg),
body height (1.82 6 0.15 m), and age (28 6 8 yr) were
Statistical Analysis
recorded after receipt of a signed consent from each
Means 6 SD were calculated for each of the biomechanical
participant. Before data collection, the research project was
parameters. Paired (samples) t-tests were used to detect
reviewed and approved by the Institutional Review Board at
significant differences in the kinematic mean scores for the
Georgia State University.
different lift types (a = 0.01). Calculated p values lower than
0.01 were considered evidence for statistical significance.
Protocol
Four synchronized video cameras (60 Hz) were used to
RESULTS
quantify the 3-dimensional analysis. The cameras were
oriented to avoid any possibility of the spotters, judges, and
Absolute and relative angles were calculated geometrically
weight plates obstructing the camera’s view of the competalong with the 3-dimensional linear and angular kinematics of
itors (i.e., body landmarks).
A peak performance video/
analog motion measurement
system was used to extract
kinematic data from the condiTABLE 2. Relative angles.
tioned video signals (17), and
Lift type
Relative joint angle (deg)
then data were smoothed using
a Butterworth digital filter
Hip
Squat
57.85 6 7.88*
67.32 6 9.89*
81.77 6 6.03*
(cutoff frequency 6 Hz). Four
Deadlift
69.07 6 8.41*
85.38 6 7.29*
95.63 6 8.14*
bilateral joint centers (shoulder,
Knee
hip, knee, and ankle) and 2
Squat
66.23 6 7.39
82.95 6 8.00*
101.21 6 6.41*
podiatric landmarks (lateral asDeadlift
125.72 6 8.04*
142.43 6 9.09
149.85 6 7.21*
pect of the calcaneus and
Ankle
Squat
55.10 6 6.38*
67.41 6 7.56*
75.86 6 7.34*
lateral aspect of the 5th metaDeadlift
46.34 6 7.51*
63.59 6 6.95*
70.74 6 7.15*
tarsal) were manually digitized.
P1 (begin ascent)
P2 (peak bar velocity)
P3 (sticking point)
In addition, hand and bar
contact points were included
*Significance (p , 0.01).
for the deadlift to accurately
measure bar velocity. Also, the
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the following parameters: bar,
shoulder, hip; knee, and ankle.
It was observed that, during the
deadlift, certain body segments
ascended before barbell LO, so
the ‘‘ascent phase’’ was defined
as the upward movement of the
barbell, unless otherwise stated.
Vertical Bar Velocity (Sticking
Point)
Each kinematic variable was
reported at 3 different points:
P1 signified the start of the
ascent phase; P2 represents the
first point where vertical bar
momentum begins to diminish;
and P3 represents the first point
of pronounced acceleration
(sticking point) after the previous phase. The sticking point
is an important position because
if the lifter is unable to overcome the inertia of the lifterbarbell system and increase
vertical velocity at P3, the lift
will not be successful.
Vertical bar velocity during
the ascent phase was used to
identify the sticking region.
Figures 1 and 2 illustrate the
sticking point associated with
the squat and the conventional
style deadlift. A significant
difference (p , 0.01) exists
between the squat and deadlift
at P1 but not at P2 and P3.
Figure 3. Squat—Kneeangle vs. hip angle.
TABLE 3. Absolute angles.
Lift type
Trunk
Squat
Deadlift
Thigh
Squat
Deadlift
Shank
Squat
Deadlift
Absolute joint angle (deg)
39.04 6 6.93*
68. 35 6 6.94*
39.47 6 7.20*
60.96 6 6.69*
40.58 6 6.29*
58.30 6 7.15*
23.46 6 2.92*
40.39 6 2.94*
26.39 6 2.89*
51.48 6 2.97*
32.32 6 2.01*
57.50 6 2.94*
55.10 6 6.38*
46.34 6 7.51*
P1 (begin ascent)
67.41 6 7.56*
63.59 6 6.95*
P2 (peak bar velocity)
75.86 6 7.34*
70.79 6 7.15*
P3 (sticking point)
*Significance (p , 0.01).
Angular Positions
Each parameter selected for
analysis indicated significantly
different (p , 0.01) relative
angular positions at the selected points. The hip and knee
angular displacements for the
squat displayed relatively equal
changes throughout the sticking point region at 14.45" and
10.25", respectively.
The trunk demonstrated a decrease in angular position (2.66")
during the sticking region of the
deadlift, whereas hip extension
increased (10.25"). Similarly,
during the squat, the trunk
displayed minimal angular
Figure 4. Deadlift—Knee angle vs. hip angle.
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Kinematic Analysis of Squat and Deadlift
and ankle angular positions
but also displayed different
TABLE 4. Segmental lengths.
bar velocities. These findings
support the argument that the
Lift type
Arm (m)
Trunk (m)
Thigh (m)
Shank (m)
sticking point mechanisms difSquat
0.62 6 0.06
0.54 6 0.07*
0.55 6 0.06
0.46 6 0.05
fer between the squat and
Deadlift
0.61 6 0.06
0.49 6 0.04*
0.55 6 0.05
0.46 6 0.04
the conventional- style deadlift
caused, in part, by biomechan*Significance (p , 0.01).
ical and physiologic factors
affecting muscle force production. Some of the variability
among the kinematic parameters could be attributed to the
change (1.11"), whereas the hip exhibited 14.45" of extension.
The absolute thigh angle at the sticking point for the squat and
differing skill levels or differences in antropometric measurements between the individual lifters. Further research in this
deadlift were 32.54" and 57.42", respectively.
area should investigate how high-skill level competitors
Knee Angle Versus Hip angle
negotiate the sticking point region as compared with lesserThe deadlift showed 3 distinct or segmented phases defined
skilled lifters.
by a dominant joint action: LO, knee extension; KP, hip
The back squat exercise is considered paradoxical because
extension; and LC, knee/hip extension. The squat lift
of the cocontracting antagonistic muscles of the lower
produced a linear relationship between the joint movements,
extremities during the execution phase. Lombard and Abbott
illustrating a more synergistic or simultaneous movement.
(13) described the phenomenon involving bi-articulate
muscles in a manner that joint movement is determined by
Anthropometric Measures
the dominant muscle moment about that particular joint
These data were used in a quantitative manner to substantiate
regardless of the muscle’s multifunctional role. The relative
how segmental lengths may influence and alter moment arm
knee and hip angular displacements during the back squat
lengths between the different lift types. Only trunk length was
movement display similar rates of change throughout the
significantly different (p , 0.01) between the lift types.
‘‘sticking point’’ region (Table 2). Figure 3 depicts a relatively
linear relationship between the knee and hip throughout the
DISCUSSION
ascent phase of the squat, a condition during which cocontraction of the rectus femoris and the hamstring group (biceps
A more detailed kinematic model would have been preferred,
femoris, semitendenosus, and semimembranosus) is evident. In
but the USPF regulations would not permit the use of reflecthis case, the extensor muscle moment generated at the hip by
tive markers during competition, which could have potenthe hamstrings is in excess of the flexor muscle moment of the
tially impeded the performance of the lifters. However, the
rectus femoris. Similarly, at the knee, the extensor moment of
powerlifting championship setting provided an ideal opporthe quadriceps dominates the flexor muscle moment of the
tunity to analyze individuals performing the squat and deadlift
hamstring group (19,22). Bar velocities quantified during
while lifting extremely heavy loads. Even though the lifts
the ascent phase of the squat implies the net extensor moment
demonstrate fundamental differences and use different lifting
is diminished at the ‘‘sticking point’’ region (Figure 1). In
strategies, a detailed analysis was used to address a common
addition, the mean absolute knee angle (Table 3) reported at
misconception that a cross-over effect exists between the lifts.
the sticking point is similar to past research findings (16).
The most obvious differences between the squat and deadlift
Conversely, the deadlift exhibits different lifting mechanics
are the placement of the barbell and the lifter’s body position
as compared with the squat, with the most obvious being
during the execution of the lifts; however, the kinematic
the 3 distinct stages (Figure 4) identified during the execution
differences between the lifts are not as evident without motion
or ascent phase: LO, KP, and LC. Interestingly, these indeanalysis instrumentation. The deadlift, unlike the back squat,
pendent phases have never been clearly defined in previous
consists only of an ‘‘upward’’ movement when performed in
research, and the availability of this information could
competition, so an analysis of the ascent phase was selected
challenge the current training methods that target the
for 2 primary reasons: a) it was common between lift types
sticking point in the deadlift. The different phases were
and b) it contained the sticking point for both movements.
defined based on the kinematics and further identified by the
The statistical analysis revealed significant differences
barbell location relative to anatomic landmarks. The LO
between the 2 lifts for the selected kinematic parameters
phase begins with the weight on the floor and proceeds until
(p , 0.01). To identify the sticking point for the squat and
the barbell nears the tibial tuberosity (approximately 6 cm
deadlift, bar velocity was selected because it best represents
distal to the patella). The movement exhibited predominant
the performance and outcome of the overall lift (Table 1). It
knee extension throughout the entire phase (Table 2), and the
was shown that the sticking point of the squat (Figure 1) and
trunk angle actually decreased, indicating an increase in trunk
deadlift (Figure 2) not only occurred at different hip, knee,
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lean during the initial phase of the lift (Table 3). The second
stage was defined as the distance between the tibial
tuberosity to a point approximately 6 cm proximal to the
patella. During this phase of the lift, the movement was
dominated by hip extension with relatively minimal knee
extension. An important note, the KP stage includes the
sticking point position, which is located near the inferior
portion of the patella. The final stage of the deadlift (LC)
transitions from the KP phase until the body is standing
completely erect. The LC portion of the lift demonstrated
a combination of both hip and knee extension. The deadlift
does not necessarily follow the Lombard model because the
execution of the lift is partitioned into 3 distinct phases.
The segmental trunk length was defined as the distance
between the hip and shoulder joint centers. The relative trunk
lengths differed (p , 0.01) between the squat and deadlift
(Table 4), suggesting the lifters demonstrated different
postural positions during the execution phase of the lifts.
During the back squat, lifters were able to maintain lumbar
lordosis with a slightly arched but rigid spinal column.
However, the deadlift exhibited a different trunk configuration, which suggests that under maximal load conditions, the
spinal column displays an abnormal curvature of the spine
during the execution of the deadlift. Specifically, the trunk
was unable to maintain lumbar lordosis, and a prominent
kyphotic condition was evident at the thoracic region of the
spinal column, which produced a rounded back posture. It
has been reported that maximal and submaximal deadlifts
demonstrate different lifting techniques and require different
lifting strategies (10).
In summary, the sticking point for both the squat and
deadlift identified the portion of the lift where the involved
muscle groups are disadvantaged, possibly because of
anatomic (bone architecture and alignment) and mechanical
(resultant muscle forces and moments) factors specific to that
region. The ‘‘sticking point’’ is a position common to each lift
but occurred at 2 distinctly different locations during the
ascent. Three absolute conclusions are drawn from the data,
supporting reasons why the lifts are different: a) evidence
indicates that the squat represents a synergistic or simultaneous movement, whereas the deadlift demonstrates a sequential or segmented movement; b) both lifts demonstrate
different sticking point locations, indicating different lifting
strategies supported by angular position and kinematic
measurements; and c) the squat and deadlift exhibited
different trunk configurations, which had a direct influence
on the lifting techniques under maximal load conditions. The
kinematic analysis of the squat and the conventional deadlift
indicate that the individual lifts are markedly different,
implying that no direct or specific cross-over effect exists
between the individual lifts. Furthermore, insight into possible
causes for the noted drop in vertical bar velocity at the key
positions during the ascent cannot be clearly gained from the
results of this study. Because of the complicated musculoskeletal mechanics of the numerous bi-articulate muscles
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involved in the execution of the squat and conventional style
deadlift, interpretations of the resultant forces and moments
are difficult. Although the kinematic data reaffirmed that
there may be changes in muscle action, mechanical disadvantages, muscle angle of pull, and muscle length-tension
relationships near this part of the movement, a biomechanical
dynamic model is needed before the musculoskeletal dynamics can be explained adequately. The scope of this analysis was
to determine gross kinematic differences between the back
squat and the conventional style deadlift.
PRACTICAL APPLICATIONS
Currently, a large portion of the powerlifting community
assumes that the sticking point for the deadlift occurs
approximately at knee level. This assumption was supported
by the findings of this study; however, momentum began to
diminish before the sticking point. A popular exercise for
training the sticking point of the deadlift is referred to as
a ‘‘lockout’’ or ‘‘partial deadlift’’ performed using a ‘‘power
rack.’’ Typically, lifters place the barbell approximately at knee
level and proceed to lift the bar from this starting position until
the hips and knees are fully extended. In retrospect, as the
results suggest, starting the partial deadlift at the knees may be
incorrect because the findings from the analysis indicated that
vertical bar momentum began to decrease before the bar
reached the knee position. Therefore, in contradiction with
current training methods, the barbell should be positioned
approximately 6 cm below the knees to target the entire
region, signifying a decrease in momentum including the
sticking point. The problem most people encounter while
performing lockouts is the inability to replicate body position
specific to the deadlift at that point of the lift. Performing
lockouts improperly on a regular basis could potentially have
a negative affect on the deadlift technique. Also, poor
technique may inhibit the recruitment process of the involved
musculature in regard to the biomechanical factors affecting
muscle force production. Contrary with popular belief,
deadlifts should not be eliminated from training programs
and replaced with squat exercises. Rather, the deadlift should
be properly and strategically placed in a periodized training
regimen to maximize performance results. In conclusion, on
the basis of the findings from this analysis, the best way to
improve the deadlift is to deadlift.
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