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INFLUENCE OF FOOTWEAR TYPE ON BARBELL BACK
SQUAT USING 50, 70, AND 90% OF ONE REPETITION
MAXIMUM:ABIOMECHANICAL ANALYSIS
JOHN W. WHITTING,RUDI A. MEIR,ZACHARY J. CROWLEY-MCHATTAN,AND RYAN C. HOLDING
School of Health and Human Sciences, Southern Cross University, Lismore, Australia
ABSTRACT
Whitting, JW, Meir, RA, Crowley-McHattan, ZJ, and
Holding, RC. Influence of footwear type on barbell back squat
using 50, 70, and 90% of one repetition maximum: a bio-
mechanical analysis. J Strength Cond Res 30(4): 1085–1092,
2016—The effect of footwear type was investigated during the
barbell back squat using three-dimensional motion analysis and
ground reaction force data. Nine male participants (mean
age = 26.4 65.4 years, height = 1.79 60.08 m, and mass =
84.7 616.1 kg) completed 2 experimental testing sessions
wearing 2 different forms of training footwear: (a) standard
sports trainers (running shoes [RS]) and (b) specialized
weightlifting shoes (WS). On each test day, participants com-
pleted a sequence of 5, 3, and 1 repetitions of a barbell back
squat using 50, 70, and 90%, respectively, of their 1 repetition
maximum (1RM) load in each of the shoe conditions. Shoe
order, which was initially randomly assigned for test day 1,
was reversed on test day 2. Significant main effects were found
for peak dorsiflexion of both left (p,0.001) and right (p,
0.001) ankles. Pairwise post hoc comparisons showed that the
RS condition exhibited significantly more dorsiflexion com-
pared with the WS condition in both left and right ankles. There
was also a significant main effect of load (%1RM) within the left
ankle (p,0.01) with post hoc comparisons showing that there
was a significant increase in peak dorsiflexion angle from 50 to
90% (p#0.05) and 70–90% of 1RM (p#0.05) but no
difference between 50 and 70% of 1RM (p= 1.000). These
findings indicate that further investigation is necessary to sub-
stantiate claims regarding the benefits of wearing WS during
resistance training exercises targeting the squat movement.
KEY WORDS squat technique, footwear, 3D motion analysis,
ground reaction force
INTRODUCTION
Squat movements have direct relevance to a range of
functional movement patterns observed both in
sport and daily life (4,16). The barbell back squat
is a primary exercise used in many athletic training
programs to develop lower body strength and power (16,24).
Its use, however, is not just limited to athletic populations but
also used extensively in rehabilitation (1). As the squat in-
volves a closed-chain weight-bearing stance, the hamstring
muscles are activated to oppose anterior tibial translation
forces caused by the quadriceps muscles. This results in less
strain being placed on the anterior cruciate ligament (ACL)
(19). Therefore, this makes the squat exercise a superior ACL
rehabilitation exercise to the leg extension exercise (24).
Depending on the objective of the exercise, squats may be
performed as a body weight only movement or “loaded” with
additional weight. Regardless, acute and chronic training
effects are generally most pronounced on the neuromuscular
components and associated connective tissues of the knee, hip,
and lower back (7,10). The squat movement can be performed
under many variations of technique. Squat depth is one aspect
of technique that can vary greatly and is typically prescribed
based on the objectives of training. Strength and conditioning
coaches typically categorize squats into 3 basic groupings
based on depth. These are (a) partial squats represented by
knee flexion of 408, (b) half squats indicated by knee flexion
of 70–1008, and (c) deep squats represented by knee flexion of
greater than 1008. A bodyweight squat at or below 908of
flexion can be used as a simple measure of total body move-
ment efficiency (16). Poor ankle mobility and a lack of flexi-
bility at the hips are also factors that can affect technique by
resulting in the lifter adopting a more pronounced forward
lean at the hips. This is often cited as a common technique
error (6,8), and it has been speculated that adopting such
a position may lead to injury by increasing compressive and
shear forces in the lumbar spine (11,14,25). Interestingly,
despite the increase in lumbar loading associated with exces-
sive trunk lean, as cited by a number of authors in recent years,
the National Strength and Conditioning Association position
paper on the squat exercise (3) suggests that lifters restrict the
forward movement of their knees, which can, in turn, cause
the lifter to lean further forward with the trunk (11,18).
Address correspondence to Rudi Meir, rudi.meir@scu.edu.au.
30(4)/1085–1092
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The barbell back squat is a primary exercise in the training
programs of athletes who compete in International Weightlift-
ing Federation (IWF) and International Powerlifting Federa-
tion (IPF) competitions. Furthermore, the barbell back squat is
also one of the 3 competition lifts used in IPF events. Each of
these organizations has rules related to competition judging
and the use of equipment by participants. One such rule
relates to competitors having to wear specified footwear. In
the case of the sport of weightlifting, Rule 4.2.1 of the IWF
Technical and Competition Rules and Regulations states that
“athletes must wear footwear (weightlifting shoes [WS] or
boots) to protect their feet and provide stability and a firm
stance on the competition platform” ((15), p. 31).
To satisfy the mandate of the IWF, WS are designed with
a stiff noncompressible flat sole and a raised heel (approx-
imately 2.5 cm). A metatarsal strap is also used to increase
lateral stability by lifting and supporting the transverse arch
of the foot. It is suggested that such a design is beneficial to
the lifter by limiting flexion and torsion of the sole when
under load, without compromising ankle range of motion,
thus increasing stability (21). The elevated heel is said to
function by allowing lifters to keep their knees forward with-
out being affected by a limited ankle dorsiflexion range of
motion, thus making it easier for the lifter to maintain a more
upright trunk to minimize external torque and subsequent
compressive and shear forces in the lumbar spine (22). Not-
withstanding these proposed benefits, the recreational lifter
and competitive athlete, who use resistance training to help
enhance their performance, typically wear standard sports
shoes or other forms of footwear when undertaking resis-
tance training (22). These types of footwear do not have the
design characteristics of the WS as described above and
would likely provide less stability when under load.
Sato et al. (22) has conducted a preliminary investigation
that supports the use of a specialized WS. These researchers
used a basic two-dimensional kinematic analysis of three dis-
placement variables to compare the use of WS with standard
sports shoes while performing the barbell back squat (60% of
1 repetition maximum [1RM]). Two-dimensional kinematic
information is inherently problematic due to errors of per-
spective, not to mention its inability to comprehensively
answer questions regarding multiplanar kinematic and kinetic
between-shoe differences (7). Therefore, this study used
a more sophisticated three-dimensional (3D) motion capture
system to compare the use of WS to standard running shoes
(RS) while performing the barbell back squat. Ground reac-
tion force data were also used to track motion of the center of
pressure (COP) for each participant. Loads of 50, 70, and 90%
of 1RM were prescribed to determine whether any significant
differences in key kinematic variables were observed. It was
hypothesized that the use of specialized weightlifting foot-
wear would positively influence the selected biomechanical
variables being investigated during all barbell back squats.
Specifically, it was hypothesized that barbell back squats
under all loads would result in less ankle dorsiflexion, less
forward trunk lean, and less movement (more stability) of
the COP in the WS condition versus the RS condition.
METHODS
Experimental Approach to the Problem
A within-subject, counter-balanced experimental design was
used to determine the impact of the 2 different types of
footwear (WS = adipower weightlifting shoe; RS = adidas
Response Cushion 22.0) on barbell back squat technique
under different %1RM loads (independent variables). Joint
kinematics and COP data (dependent variables) were re-
corded to determine whether there were technique benefits
(e.g., optimization of joint kinematics and increased stability).
Participants completed 5, 3, and 1 repetition, representing 3
sets, of a barbell back squat pattern using 50, 70, and 90% of
their predetermined 1RM, respectively, while wearing each
type of footwear (experimental condition). All shoes in this
study were new and only used by participants with the same
shoe size during this study. A total of 6 sets of the exercise
were completed on each of 2 separate testing occasions.
Subjects
Nine male participants (mean age = 26.4 65.4 years, age
range = 18–33 years, height = 1.79 60.08 m, and mass =
84.7 616.1 kg) volunteered to participate in this study. Using
a priori power analysis (G*power 3, version 3.1.2) (9) with
an effect size of 0.5, power of 0.80, and alevel of 0.05,
the predicted minimum number of participants would be
8 for detecting within-factor differences using a repeated-
measures analysis of variance. All participants were actively
engaged in regular weekly resistance training at the time
of their participation in this study. Participants also had
a minimum of 3 years experience using the barbell back squat
in their own training. Participants were informed of the bene-
fits and risks of the investigation before signing an institution-
ally approved informed consent document to participate in
this study. Participants were advised that they could withdraw
their consent at any time. All procedures were approved by
the Southern Cross University Human Research Ethics Com-
mittee (approval number: ECN-13–210).
Procedures
All testing sessions were conducted at the same time of day
(between 1.00 and 4.00 PM) and in the same location. All
participants were asked to attend a familiarization session
1 week before testing. At this session, test procedures were
demonstrated, and potential experimental risks were identi-
fied (e.g., injury). An information sheet detailing the purpose
of the study and the nature of participants’ involvement was
provided. On expressing a willingness to participate in this
project, participants were asked to sign informed consent
and complete a standard preparticipation health screening
questionnaire. Before the first data collection session (test
session 2), participants returned at a mutually agreed time
(between 1:00 and 4.00 PM) and day to have their baseline
measures collected. This required the recording of basic
Footwear Effects During a Barbell Back Squat
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anatomical measures and completion of their 1RM barbell
back squat test (test session 1). The 1RM squat test was
completed while wearing normal training footwear, as per
the procedure outlined by Harman and Garhammer (13).
Squat technique, using an unloaded Olympic bar, was
initially assessed by a Certified Strength and Conditioning
Specialist before each participant completing their 1RM test;
this same coach supervised all subsequent tests during data
collection involving the different shoe conditions. Partic-
ipants presented using a range of depths (from bottom of
hamstrings parallel to floor to hamstrings touching the back
of the lower leg) at which they normally identified the
bottom of their squat movement in their regular training.
Notwithstanding the within-subject design nature of this
study, squat depth was determined visually and standardized
for each participant for the 1RM test and under each of the
subsequent shoe conditions. All 1RM tests were conducted
in a power rack with depth of squat visually determined as
being when the top of the thighs was parallel with the floor
and hip crease in line with or slightly below the knee.
Before all test occasions, participants were instructed not to
complete any lower body training in the 24 hours immedi-
ately before their testing session. Participants were also
advised to abstain from consuming a heavy meal or any
caffeine-based drinks in the 2 hours before each of the 3
testing sessions and to consume 500 ml of water in the
30 minutes before testing. Participants had to be free from any
form of injury and illness to participate in each testing session.
Each testing session was separated by a minimum of 48 hours.
On arrival at test session 2, participants were assigned
(counterbalanced design) the first pair of shoes (experimental
condition) to be worn in that session; the order of shoe was
reversed for each participant on the third and last test occasion.
Participants were then prepared for testing by the placement of
27 retro-reflective markers on the barbell, head, trunk, pelvis,
lower limbs, and feet to define a 10-segment model (modified
Plug-In-Gait). Markers identifying the foot segment were
placed on the shoes (Figure 1). The 3D coordinates of these
markers were captured using 10 high-speed (100 Hz) cameras
(Vicon T40-S, Oxford, United Kingdom) and using Nexus
software (version 1.8.4, 2013).
A Butterworth fourth-order
low-pass filter was used to filter
marker trajectories (f
c
=4Hz)
(12), and 3D marker coordinates
were used to calculate the fol-
lowing kinematic variables for
each squat in the sagittal plane:
peak left and right ankle dorsi-
flexion angles; minimum left and
right knee flexion angles (thigh
relative to shank); minimum left
and right hip flexion angles (pel-
vis relative to thigh); minimum
left and right thigh inclination
angles (thigh relative to the horizontal—determinant of squat
depth); and peak forward trunk lean angle (trunk relative to the
vertical).
Ground reaction force data were captured (1,000 Hz)
during each trial as participants stood with both feet on
a single Kistler force plate (Type 9287; Winterthur, Switzer-
land). The same Nexus software was used for data processing,
and ground reaction forces were also filtered (f
c
=50Hz)with
a Butterworth fourth-order low-pass filter. The filtered data
were used to calculate COP peak displacements in anterior–
posterior (A-P) and medio–lateral (M-L) directions.
Squatting Sequence
After participant preparation, each test occasion started with
participants completing their normal resistance training
session warm-up. They were then required to complete
the following sequence of squats: (a) a set of 5 body weight
only (i.e., no load) squats followed by 60 seconds rest; (b)
a set of 5 squats with an unloaded Olympic bar followed by
2 minutes rest; (c) a set of 5 squats using a load equivalent to
50% of their 1RM followed by a 2–3 minutes rest; (d) a set of
3 squats using a load equivalent to 70% of their 1RM fol-
lowed by 4 minutes rest; and (e) 1 squat using a load equiv-
alent to 90% of their 1RM. A 5 minute rest period followed
this first sequence and was used to allow participants to
change into their assigned alternate shoes for the second
series of squats. The second series of squats started with
the completion of the set of 5 unloaded Olympic bar squats
and then continued in the same order as described for the
first squat sequence. The bar was located in the high bar
position (6) for all repetitions and by all participants.
Verbal feedback was given when participants reached the
required squat depth as described above. To standardize
squat repetition speed, thereby minimizing unwanted accel-
erations and variations (23), participants were instructed to
squat in time with a digital metronome. In doing so, they
executed each full squat movement approximating a tempo
equivalent to 1 second down and 1 second up (1-0-1). At the
shoe changeover from the first series of squats and after
the second and final series, each participant was asked to
Figure 1. Placement of retro-reflective markers to identify foot segment.
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rate the perceived stability and comfort of each type of shoe.
This was performed with the participant sitting on their own
and indicating their responses for each shoe by placing
a “cross” on a 100 mm visual analog scale. The statement
“least comfortable (or stable) shoes I have ever worn” rep-
resenting the absolute zero point and the statement “most
comfortable (or stable) shoes I have ever worn” being the
maximum value possible for each question. A similar analog
scale was also used for perceived shoe stability.
Statistical Analyses
For each variable of interest, a two-factor (shoe 3load)
repeated-measures general linear model was then used to
determine whether there were main effects of shoe condition
(WS and RS) or load condition (50, 70, and 90% 1RM) and
whether there were any shoe 3load interactions. If any
main effects or interactions were detected, then post hoc
analysis with Bonferroni adjustment was conducted to iden-
tify the significant difference between mean values. Effect
sizes using Pearson correlation rwere also calculated for
all comparisons. Comparisons between shoe comfort and
stability were determined using a paired t-test. All statistical
analyses were conducted using SPSS version 20 for
Windows with an alevel set at 0.05.
RESULTS
Initial data analysis involved a day 3shoe 3load repeated-
measures general linear model assessment as data collection
procedures were repeated twice. All variables showed no
main effect of day and no interactions with day (day 3shoe,
day 3load, or day 3shoe 3load). Subsequent paired t-tests
for all variables were then conducted, and no differences
were found between days again for all variables of interest.
Therefore, the 2 days were collapsed into 1 session.
Peak Ankle Dorsiflexion Angle
There were no shoe 3load interactions found in either the
left (p= 0.447, r= 0.22) or right (p= 0.921, r= 0.07) ankles.
Significant main effects for shoe were found for peak dorsi-
flexion of both left (p,0.001; r= 0.88) and right (p,0.001;
r= 0.85) ankles (Figure 2 and Table 1). Pairwise post hoc
comparisons showed that the RS condition exhibited signif-
icantly higher dorsiflexion compared to the WS condition in
both left and right ankles. There was also a significant main
effect of load (%1RM) within the left ankle (p= 0.004; r=
0.53) with post hoc comparisons showing that there was
a significant increase in peak dorsiflexion angle from 50 to
90% (p= 0.037) and 70–90% of 1RM (p= 0.034) but no
difference between 50 and 70% of 1RM (p= 1.000). Load
main effect analysis for the right ankle showed no signifi-
cance (p= 0.071; r= 0.41).
Minimum Knee Flexion Angle
There were no significant shoe 3load interaction effects in
either the left (p= 0.527; r= 0.18) or right (p= 0.512; r=
0.18) minimum knee flexion angles (Table 1). Main effects
analysis of shoe showed no significance for either the left
(p= 0.125; r= 0.36) or right (p= 0.750; r= 0.08), and also no
significant effect of load in either the left (p= 0.468; r= 0.19)
or right (p= 0.135; r= 0.35) minimum knee flexion angles.
Minimum Thigh Inclination Angle
Shoe x load analysis revealed that there were no significant
interactions for either the left (p=0.465;r= 0.21) or right (p=
0.976; r= 0.03) minimum thigh angles (Table 1). Main effect
analysis of shoe indicated no sig-
nificance for both the left (p=
0.978; r=0.008)andright(p=
0.862; r= 0.04) minimum thigh
inclination angles. Load main
effect analysis showed a signifi-
cant effect for both the left (p=
0.020; r= 0.48) and right thigh
(p=0.045;r=0.44).Posthoc
analysis of the left minimum
thigh angle revealed that there
were no differences when com-
paring 50–70% (p= 0.100) and
50–90% (p=0.094);however,
there was a significant increase
from 70 to 90% (p=0.035).
For the right minimum thigh
angle, post hoc analysis revealed
that there were no differences
when comparing any of the 3
load conditions (50–70%, p=
0.100; 50–90%, p=0.133;and
70–90%, p=0.162).
Figure 2. Mean (6SD) shoe main effects for peak dorsiflexion angles of the left and right ankles (N=9).
*Indicates a significant difference between shoes (p#0.05).
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TABLE 1. Mean (6SD) of recorded variables displayed for each shoe (WS and RS) and each load (50, 70, and 90% 1RM) condition (N= 9).*
Variables
50% 1RM 70% 1RM 90% 1RM
Left Right Left Right Left Right
WS RS WS RS WS RS WS RS WS RS WS RS
Peak ankle
dorsiflexion
angle (8)†z§
25.2 (4.2) 29.3 (3.5) 25.1 (6.8) 31.0 (4.6) 24.9 (4.5) 29.7 (3.4) 25.0 (6.7) 30.8 (4.3) 26.0 (4.5) 31.1 (4.0) 26.0 (6.8) 31.7 (5.1)
Minimum knee
flexion
angle (8)
54.6 (10.9) 56.9 (11.0) 53.1 (12.4) 54.3 (11.8) 55.5 (10.8) 56.4 (9.6) 54.3 (12.2) 54.5 (10.4) 56.1 (11.7) 57.6 (11.9) 55.8 (13.8) 55.7 (12.7)
Minimum
thigh
inclination
angle (8)k
16.8 (10.2) 16.5 (10.1) 16.7 (9.6) 16.5 (9.6) 17.0 (11.2) 16.6 (10.4) 16.7 (9.6) 16.7 (10.0) 17.8 (10.1) 18.4 (10.8) 18.2 (10.4) 18.1 (10.7)
Minimum hip
flexion
angle (8)
61.8 (9.3) 61.7 (10.4) 61.2 (8.2) 60.9 (9.6) 63.2 (10.0) 62.3 (9.1) 62.4 (8.6) 62.0 (8.1) 64.9 (10.5) 64.8 (12.9) 64.2 (11.7) 64.1 (10.9)
WS RS WS RS WS RS
Peak trunk lean angle (8)¶# 38.0 (6.7) 38.2 (6.4) 38.9 (6.5) 39.7 (6.8) 41.5 (6.8) 41.3 (6.5)
COP deviation (A-P) (mm)**†† 148.3 (38.8) 144.0 (28.1) 162.6 (61.0) 141.3 (37.1) 136.2 (56.7) 118.4 (41.1)
COP deviation (M-L) (mm) 135.7 (60.0) 120.8 (45.2) 143.1 (107.3) 151.9 (96.5) 122.0 (95.7) 139.8 (92.5)
*1RM = 1 repetition maximum; RS = running shoes; WS = weightlifting shoes; COP = center of pressure; A-P = anterior–posterior; M-L = medio–lateral.
†Significant shoe main effect (p,0.001)—increased dorsiflexion RS vs. WS.
zSignificant load main effect—post hoc comparison showing higher left ankle dorsiflexion angle for 50 vs. 70% 1RM (p,0.037).
§Significant load main effect—post hoc comparison showing higher left ankle dorsiflexion angle for 70 vs. 90% 1RM (p,0.034).
kSignificant load main effect—post hoc comparison showing an increase in minimum thigh angle for 70 vs. 90% 1RM (p,0.035).
¶Significant load main effect—post hoc comparison showing an increase in peak trunk lean angle for 50 vs. 90% 1RM (p,0.022).
#Significant load main effect—post hoc comparison showing an increase in peak trunk lean angle for 70 vs. 90% 1RM (p,0.016).
**Significant shoe main effect (p,0.010)—larger peak COP (A-P) movement WS vs. RS.
††Significant load main effect—post hoc comparison showing reduction in peak COP (A-P) from 70 to 90% 1RM (p,0.049).
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Minimum Hip Flexion Angle
There were no significant shoe 3load interactions for
either the left (p=0.735;r= 0.11) or right (p=0.90;r=
0.05) minimum hip flexion angles (Table 1). Analysis of
shoe main effect indicated no significance for both the left
(p=0.662;r= 0.11) and right (p=0.788;r= 0.06) minimum
hip flexion angles. Load main effect analysis showed a sig-
nificant effect for the left hip (p= 0.019; r=0.50)but
not for the right hip (p=0.068;r= 0.44). However, post
hocloadanalysesfortheleftminimumhipflexionangle
revealed that there were no specific between-load differ-
ences (50–70%, p= 0.334; 50–90%, p=0.059;and
70–90%, p=0.103).
Peak Trunk Lean Angle
There was no significant shoe 3load interaction for the
peak trunk lean angle (p= 0.308; r= 0.26). Shoe main effect
analysis indicated no significance for the peak trunk lean
angle (p= 0.502; r= 0.16). However, a significant load main
effect was found (p= 0.006; r= 0.58) (Table 1). Post hoc
analyses for the peak trunk lean angle found no difference
between 50 and 70% (p= 0.213), but there was a significant
increase from 50 to 90% (p= 0.022) and from 70 to 90% of
1RM (p= 0.016).
Peak Center of Pressure Deviations
Analysis of peak COP (A-P) deviation showed no significant
interaction (p= 0.344; r= 0.25); however, there was a signif-
icant main effect of shoe (p= 0.010; r= 0.57; Figure 3) and
load (p= 0.038; r= 0.42). Post hoc analyses revealed a sig-
nificantly larger peak COP (A-P) movement in the WS con-
dition compared with the RS condition (p= 0.010). Analysis
of the effect of load showed
that there were no differences
between 50 and 70% (p=
1.000) or 50 and 90% of 1RM
(p= 0.273); however, there was
a significant reduction in peak
COP (A-P) from 70 to 90% of
1RM (p= 0.049). Analysis of
peak COP (M-L) deviation
showed no significant interac-
tion (p= 0.452; r= 0.20) and
no main effects of shoe (p=
0.623; r= 0.12; Figure 3) or
load (p= 0.437; r= 0.22)
(Table 1).
Perceived Shoe Comfort
and Stability
Paired t-tests indicated that par-
ticipants perceived the RS to be
significantly more comfortable
(p,0.032; mean rating = 80.4
611.9) than the WS (mean
rating = 70.2 614.9), whereas
the WS were perceived to be significantly more stable (p,
0.000; mean rating = 89.5 67.6) than the RS (mean rating =
65.9 615.5).
DISCUSSION
This project aimed to establish whether specific WS
significantly affect technique during a barbell back squat
when compared with a standard sport RS under different %
1RM loads. Although limited research has been conducted
previously (22), this study used more sophisticated method-
ology (3D motion capture) to determine differences in key
kinematic measures. It also used ground reaction force data
to determine displacement measures as indicators of stability
in A-P and M-L directions.
Confirming our hypothesis, this research revealed a signif-
icant main effect for shoe in peak left and right dorsiflexion
angles with the heel-elevated WS exhibiting significantly
lower dorsiflexion angles compared with the RS. Because of
the solid construction of the elevated heel and the absence of
a soft midsole in the WS, this finding is not surprising.
However, unlike previously reported findings (22), our anal-
yses revealed no other effect of shoe condition on any of the
selected key kinematic variables. Consequently, our hypoth-
esis that any reduction in peak dorsiflexion in the WS would
also lead to a reduction in peak forward trunk lean was not
confirmed.
It must be noted that Sato et al. (22) did not directly assess
trunk lean, and that their conclusions regarding the effect of
shoes on dorsiflexion and trunk lean are limited by this.
Nonetheless, it is reasonable to postulate that by simple
geometry, their measures of A-P bar and hip displacement
Figure 3. Mean (6SD) shoe main effects for peak center of pressure (COP) deviation (mm) in anterior–posterior
(A-P) and medio–lateral (M-L) directions (N= 9). *Indicates a significant difference between shoes (p#0.05).
Footwear Effects During a Barbell Back Squat
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could be deemed to reflect trunk lean, which is what
informed our original hypothesis. Another possible reason
for not observing an effect of shoe on trunk lean in this study
may be that participants had sufficient ankle dorsiflexion
range of motion to cope with the RS condition (as reflected
by the increase in peak dorsiflexion). This may have enabled
them to maintain a forward-knees position, a technique
advised by Fry et al. (11) and List et al. (18), to keep the
load displacing vertically over their base of support (4) with-
out needing to increase hip flexion or forward trunk lean.
Although knee position relative to the feet was not calcu-
lated in this study, it is reasonable to postulate that the
greater peak dorsiflexion angle was likely to compensate
for a lower and softer heel wedge in the RS condition to
result in a similar knee position. Furthermore, the similarities
in the kinematic measures further up the chain indicate some
between-shoe consistency in squat technique, at least in sag-
ittal kinematic minima and maxima. Future studies, however,
should investigate the impact of dorsiflexion capacity on
technique during squats in different footwear.
Our analyses have also shown that peak COP displace-
ments, typical indicators of stability and balance (17,20), dif-
fered between shoe conditions for these participants with
a significantly larger COP (A-P) displacement in the WS
condition compared to the RS condition. Even though there
was no between-shoe difference in peak M-L COP devia-
tion, these findings mean that the hypothesis that the WS
condition would lead to less overall COP movement (greater
stability) was rejected. Nonetheless, it is worth noting that
this finding was not supported by the perception of the study
participants. The results of the visual analog scale assess-
ments on both days showed that the cohort rated the WS
condition as significantly more stable than the RS condition.
One reason for this may be the assumption that reduced
amplitude of displacement in the COP is not necessarily
an indicator of greater balance, stability, or control. In fact,
researchers are now starting to postulate that these gross
measures of COP excursion fail to provide temporal infor-
mation that can help to explain strategy and control (2). It
may be that participants, who perceived the WS condition as
more stable, were more confident and therefore allowed
themselves to translate more in the A-P direction to manip-
ulate the location of the load in relation to the base of sup-
port. For instance, Croft et al. (5) demonstrated that COP
displacement was more constrained in standing balance
tasks where participants were on compliant (unstable) vs.
solid surfaces. Any future investigations of balance or stabil-
ity effects of footwear in squatting movements should there-
fore incorporate nonlinear approaches that quantify
temporal motor control strategies and responses (2).
Although there were no hypotheses developed for this
analysis, it is interesting that a load effect was observed for
COP deviations in this study. Although there was no
significant difference in peak COP (A-P) displacement between
50 and 70 and between 50 and 90% 1RM, there was
a significant reduction in peak COP (A-P) displacement from
70 to 90% of 1RM. It is reasonable to postulate that a feed-
forward mechanism was used by participants to constrain
movement in the most difficult load condition and perhaps
there is a load threshold, yet to be elucidated, that alters this.
Overall, there were no significant shoe effects in all key
selected kinematic measures, except for peak ankle dorsiflex-
ion angles. Although peak trunk lean was consistent between
shoe conditions, conclusions regarding potential lumbar
loading remain tenuous as no joint kinetics were measured
or calculated to provide more direct evidence. Future studies
should, therefore, incorporate a kinetic analysis. Nonetheless,
links between kinematics and kinetics are well established
during squatting and lifting tasks (10,11,14,24), and so the
findings of this study certainly provide a sound basis for more
work. It is also worth considering that greater peak displace-
ment in COP (A-P) deviation in the WS condition, albeit
while constraining peak angular displacements, may be an
indication that the temporal between-shoe movement pat-
terns were different. As a result, future work with the current
data set may be warranted, using more comprehensive tech-
niques such as principal component and support vector
machine analyses. Such an approach may highlight more sub-
tle shoe effects that are easily missed by traditional discrete
variable analyses such as this study. It must also be acknowl-
edged that conclusions in this study are limited by a cohort of
9 participants. However, statistical findings and inferences
were strengthened by the study design that incorporated
a repeat of measures across 2 days and across 3 load condi-
tions. Having no effect of day, for instance, enabled the data to
be collapsed into a shoe 3load design, effectively doubling
the size of the data set.
PRACTICAL APPLICATIONS
This research has been driven by practices observed in the
training environment regarding the use of different types of
footwear. To date, there is limited evidence for support of
this practice and any potential beneficial effects on lifting
performance or reducing injury risk. As is evident by the
discussion of findings in this study, the scope for studying the
effects of footwear on squat movements should be expanded
substantially. Athletes, coaches, patients, and therapists
undertake squats for many reasons and by using varying
techniques and footwear. However, it is our contention that
the results of this study question the notion that overall
technique, and therefore injury risk, may be substantially
affected by footwear typically used in weightlifting environ-
ments. Notwithstanding this, it is important that further
studies, such as those suggested in this article, are under-
taken to provide a clearer understanding of the benefits, or
otherwise, of this type of footwear to users.
ACKNOWLEDGMENTS
The authors acknowledge the support of Adidas (a.i.t) who
provided the shoes used in this study.
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