International Journal of Sports Science 2014, 4(2): 47-49
Acute Effects on Maximal Isometric Force with and
without Knee Wrap During Squat Exercise
Willy Andrade Gomes, Érica Paes Serpa, Enrico Gori Soares, Josinaldo Jarbas da Silva,
Daniel Corrêa, Fernando Henrique Domingues de Oliveira, Francisco de Abreu Neto,
Gustavo Martins, Guanis de Barros Vilela Junior, Paulo Henrique Marchetti*
Department of Human Movement Sciences, Methodist University of Piracicaba, Piracicaba, São Paulo, Brazil
Abstract The aim of this study was to investigate the acute effects on maximal isometric force without and with two
kinds of knee wraps (hard and soft) during squat exercise. Ten physical active participants were evaluated during this study.
All subjects were familiarized with the isometric squat position in all conditions: without and with knee wrap (hard and soft
stiffness). The squat exercise position was set up individually, guaranteeing their thigh parallel to the floor, the arms crossed
on the chest, and the feet were kept always in the same position for all trials and conditions. All subjects performed three
maximal isometric squat contractions in 3 different conditions: without knee wrap (WKW), with soft knee wrap (SKW) and
with hard knee wrap (HKW). The peak of force was acquired at a 100Hz sampling frequency, during 3 seconds, 5 minutes of
resting and all conditions were randomized. The results shows significant differences for peak force between conditions
WKW and HKW (P=0.029, ES=1.27, Δ%=22%]) and WKW and SKW (P=0.038, ES=1.20, Δ%=21%]). The use of the knee
wrap under the presented conditions seem to increase the maximal isometric force during the squat exercise, independent of
the level of stiffness of the knee wrap.
Keywords Biomechanics, Exercise performance, Strength
The knee wrap is an equipment commonly used by
weightlifters and powerlifters aiming to stabilize the knee, to
improve the strength performance (gain mechanical
advantage) or to improve the confidence during squat
exercises [1, 2]. The knee wrap is a long wrap of elastic
material (tick canvas interwoven with rubber filaments) with
approximately 2 meter long, which is wrapped around the
knees as tight as possible [3, 4]. There are some studies that
investigated both kinematics and kinetics of the squat
exercise using the knee wrap in powerlifters [5, 6] and
trained subjects , however little has been known about its
effects of loading capacity. Eiter et al.  studied the use of
knee wrap in powerlifters and analyzed the general
characteristics of the squat exercise (execution time,
percentage of the transition cycle (upward-downward
displacement) of the center of mass and the bar vertical
displacement) with and without knee wrap, with no
differences between them. Lake et al.  studied the use of
knee wrap in trained subjects with and without knee wrap.
The authors analyzed the ground reaction force, output of the
* Corresponding author:
email@example.com (Paulo Henrique Marchetti)
Published online at http://journal.sapub.org/sports
Copyright © 2014 Scientific & Academic Publishing. All Rights Reserved
mechanical force applied to the center of mass, vertical
impulse, horizontal displacement of the bar, mechanical
work and peak power. They observed that the elastic
properties of the knee wrap increased the production of
mechanical force by changing the squat technique.
In general, when the knee is flexed against an external
resistance during a squat exercise, the elastic material is
stretched during the lowering phase, returning this energy
during the lifting phase. This potenctial energy accumulated
is transferred to the lifter and added to the strength
performance of the movement in the concentric phase ,
and this additional effect on the strength performance is also
known as carry-over. Only two studies reported the amount
of carry-over of 19.8% in elite powerlifters  and 25,1% in
subjects trained , respectively, during squat exercise.
However, little is known about the effects of different
models (stiffness) of knee wrap in the peak force during the
squat exercise and how much carry-over can actually be
related to the knee wrap instead of the stretch-shortening
cycle. Therefore, the purposes of the present study was to
compare the acute effects on maximal isometric force
without knee wrap and two kinds of knee wrap stiffness
(hard and soft) during squat exercise.
48 Willy Andrade Gomes et al.: Acute Effects on Maximal Isometric Force
with and without Knee Wrap During Squat Exercise
Ten physical active participants were evaluated during this
study (age 24±3 years, body mass 79.9±9kg, height
175.7±3cm). All subjects were engaged in regular resistance
training routine (hypertrophy loads: 3-4 exercises for lower
limbs, 8-12 maximum repetitions) including squat exercise
(2 sessions per week) for not less than one year. The number
of subjects was determined by using the same variable from
our pilot study, and ten subjects were showed to be necessary
based on alpha level of 0.05 and a power (1-β) of 0.80 .
All subjects who participated in this study had no previous
trunk or lower limbs surgery/injury and they were evaluated
with a minimum of 48 hours without training sessions. All
the participants were instructed about the potential risks
involved, read and signed an institution-approved
informed-consent form before participating in the study. The
study was approved by the ethics committee of Methodist
University of Piracicaba (Protocol: 76/12).
Initially, all subjects were familiarized with the isometric
squat position in all conditions: without and with knee wrap
(hard and soft stiffness). The squat exercise position was set
up individually, guaranteeing their thigh parallel to the floor,
the arms crossed on the chest, and the feet were always kept
in the same position for all trials and conditions. A load cell
(CEFISE biotecnologia esportiva, Nova Odessa, Brazil) was
attached perpendicularly to the ground and in subject’s hip
by using a belt. Then, each subject performed three maximal
isometric squat contractions in 3 different conditions:
without knee wrap (WKW), with soft knee wrap (SKW) and
with hard knee wrap (HKW). For the placement of the knee
wrap we used a spiral technique as described by Coutinho ,
always by the same researcher. The peak of force was
acquired by CEFISE software at a 100Hz sampling
frequency, during 3 seconds and 5 minutes between
contractions and conditions. All conditions were randomized
and collected in one session. All the data were analyzed with
a customized program written in Matlab (Mathworks Inc.,
EUA). The peak of force was filtered with a 4th-order 10 Hz
low-pass zero-lag, Butterworth filter.
Normality and homogeneity of variances within the data
were confirmed by the Shapiro-Wilk and Levene tests,
respectively. To compare the effects of using knee wrap
(WKW, SKW and HKW) a repeated measures ANOVA
were employed. Post-hoc comparisons were performed by
using the Bonferroni test. Cohen’s formula for effect size
(ES) was used and the results were based in the following
criteria: <0.35 trivial effect; 0.35-0.80 small effect; 0.80-1.50
moderate effect; and >1.5 large effect, for recreational
trained according to Rhea . An alpha of 5% was used for
all statistical tests. The ICC was test for all trials for each
conditions (WKW= 0.96; HKW= 0.96; SKW= 0.98).
There were significant differences between peak force and
conditions: WKW and HKW (P=0.029, ES=1.27, Δ%=22%])
and WKW and SKW (P=0.038, ES=1.20, Δ%=21%]).
However, it was not observed significant differences
between kinds of knee wraps (P=0.98). Figure 1 shows the
mean and standard deviations of the peck force values for the
three testing conditions.
Figure 1. Mean ± standard deviation of the peak of force during isometric
squat for different conditions (without knee wrap, high knee wrap and soft
knee wrap, respectively). *P<0.05
The aim of this study was to compare the effect by using
different models of knee wrap (hard and soft) in peak force
of trained subjects while performing a maximum voluntary
isometric contraction (MVIC) in the squat exercise. There
were differences between the conditions HKW and WKW (P
<0.029) and between conditions WKW x SKW (P <0.038),
resulting in a carry-over of 22% (ES = 1.27) and 21% (ES =
1.20) respectively, corroborating the findings of Harman and
Related to carry-over effect observed during our study, we
could verify an increase in the external load, that was due to
the elastic energy stored in the knee wrap material under
mechanical deformation . The knee wrap is composed of
elastomeric material and polyester, and it has the ability to
suffer large deformations and return elastically to its original
shape, as springs. This elastic effect is due to the crosslink of
the polymer, which, when stretched, results in a force
capable of returning the material strands to their original
conformations without any permanent deformation (plastic
deformation) . So, this elastic energy can be transferred
into kinetic energy and added to the lifter .
Curiously, we did not observe any difference on the force
of peak between the models of knee wrap (hard x soft). This
similarity can be related to the number of laps to involve the
knees. The soft knee wrap allowed a higher number of laps
when compared to hard knee wrap (approximately, two laps).
Probably, the higher number of laps, in the soft knee wrap,
can result in a higher number of elastic fibers in parallel,
adding elastic energy and compensating the greater
resistance of the hard knee wrap . This hypothesis is
based on the principle of laminated composites cited by
International Journal of Sports Science 2014, 4(2): 47-49 49
Callister , which states that the sum of composite layers
stacked one on top of the other, resulting in a relatively high
resistance. According to specifications of the manufacturer
both wraps are composed of 70% polyester and 30%
elastodiene. However, factors such as the arrangement or
orientation of the fibers have a significant influence on the
strength and other properties of fiber reinforced composites
. It is important to emphasize that, for both models (SKW
and HKW), we used the same placing technique by the same
investigator. The present study analyzed the maximal
isometric squat exercise aiming to verify the carry-over
effect without elastic components of the muscle
(stretch-shortening cycle, SSC). Previous studies analyzed
the squat exercise with and without knee wrap in a dynamic
condition. However, the carry-over effect can be influenced
by the combination of both, SSC and elastic energy of the
knee wrap , in addition to that the velocity of motion
execution can affect the SSC response .
The acute effect on maximal isometric force during squat
exercise was to present an effective carry-over during the
squat exercise by using the knee wrap. For coaches, athletes
and sport science practitioners the use of knee wrap under the
presented conditions seem to increase the maximal isometric
force during the squat exercise, independent of level from
stiffness of knee wrap.
Conflict of Interest
There were no conflicts of interest for conducting this
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