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Quadriceps EMG muscle activation during accurate soccer instep kicking
Joanna C. Scurra; Victoria Abbotta; Nick Ballb
a Department of Sport and Exercise Science, University of Portsmouth, Portsmouth, UK b Faculty of
Health, University of Canberra, Canberra, ACT, Australia
First published on: 16 December 2010
To cite this Article Scurr, Joanna C. , Abbott, Victoria and Ball, Nick(2011) 'Quadriceps EMG muscle activation during
accurate soccer instep kicking', Journal of Sports Sciences, 29: 3, 247 — 251, First published on: 16 December 2010 (iFirst)
To link to this Article: DOI: 10.1080/02640414.2010.523085
URL: http://dx.doi.org/10.1080/02640414.2010.523085
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Quadriceps EMG muscle activation during accurate soccer instep
kicking
JOANNA C. SCURR
1
, VICTORIA ABBOTT
1
, & NICK BALL
2
1
Department of Sport and Exercise Science, University of Portsmouth, Portsmouth, UK and
2
Faculty of Health, University
of Canberra, Canberra, ACT, Australia
(Accepted 8 September 2010)
Abstract
Six competitive soccer players were recruited to examine EMG activation in three quadriceps muscles during a kicking
accuracy task. Participants performed three maximum instep place kicks of a stationary ball, 11 m perpendicular from the
centre of the goal line towards targets (0.75 m
2
) in the four corners of the goal. Surface EMG of the vastus lateralis, vastus
medialis, and rectus femoris of the kicking leg was normalized and averaged across all participants to compare between
muscles, targets, and the phase of the kick. Although no significant difference were observed between muscles or kick phases,
kicks to the right targets produced significantly greater muscle activity than those towards the left targets (P50.01). In
addition, kicks towards the top right target demonstrated significantly greater muscle activity than towards the top and
bottom left (P50.01). Under accurate soccer shooting conditions, kicks aimed to the top right corner of the goal
demonstrated a higher level of quadriceps muscle activation than those towards the other corners.
Keywords: Electromyography, vastus lateralis, vastus medialis, rectus femoris, soccer, football
Introduction
The two most common kicking actions used to score
during the 1998 soccer World Cup were the instep
kick and side-foot kick (Grant, Reilly, Williams, &
Borrie, 1998). The instep kick, whereby the ball is hit
with the dorsum of the foot, is the most powerful
kicking action in soccer (Brophy, Backus, Pansy,
Lyman, & Williams, 2007). Consequently, previous
soccer-related biomechanical research has focused
on the dynamics of the maximum instep kick, which
corresponds to the penalty or ‘‘place’’ kick (Barfield,
1998; Brophy et al., 2007; Do¨ rge et al., 1999; Do¨ rge,
Bull Andersen, Sørensen, & Simonsen, 2002;
Levanon & Dapena, 1998; Luhtanen, 1988;
Nunome, Asai, Ikegami, & Sakurai, 2002; Putnam
& Dunn, 1987).
Previous research has examined the biomechanics
of soccer movements in detail (Lees, 1996; Lees &
Nolan, 1998), although only a limited number of
studies have used electromyographic (EMG) analysis
to observe muscle activation during the kick (De
Proft, Clarys, Bollens, Cabri, & Dufour, 1988;
Do¨rge et al., 1999; Kellis, Katis, & Gissis, 2004;
McCrudden & Reilly, 1993; McDonald, 2002;
Orchard, Walt, McIntosh, & Garlick, 2002).
Although the whole body is known to influence
muscular actions during the approach and kick, the
quadriceps muscle group plays a vital role in the
rapid extension of the knee joint in preparation for
contact with the ball (Kellis & Katis, 2007).
Previously reported normalized EMG values in
maximum instep kicking range from 67% to 90%
for the vastus medialis, 59% to 86% for the rectus
femoris, and 64% to 102% for the vastus lateralis
(De Proft et al., 1988; Do¨ rge et al., 1999; Manolo-
poulos, Papadopoulous, & Kellis, 2006). This
demonstrates the variability in previous research,
which limits conclusions regarding the importance of
each muscle during soccer kicking.
A maximum kick is not necessarily an accurate
kick (Winter, 1990). Although studies on muscle
activation patterns during accurate kicking are
limited (Dicks & Kingman, 2005), previous research
has indicated that muscle activation patterns may be
more complex during accurate kicking to achieve a
finer control of lower limb movement in order to
make the necessary adjustments in muscular activity
(Kellis & Katis, 2007). Accurate kicking is known to
reduce the speed of the action compared with
Correspondence: J. C. Scurr, Department of Sport and Exercise Science, University of Portsmouth, Spinna ker Building, Cambridge Road, Portsmouth PO1
2ER, UK. E-mail: joanna.scurr@port.ac.uk
Journal of Sports Sciences, February 1st 2011; 29(3): 247–251
ISSN 0264-0414 print/ISSN 1466-447X online Ó2011 Taylor & Francis
DOI: 10.1080/02640414.2010.523085
Downloaded By: [University of Canberra] At: 02:56 18 January 2011
maximum kicking (Kellis & Katis, 2007). In addi-
tion, Kellis and Katis (2007) suggested that differ-
ences in muscle activity may occur during accurate
kicking against a high or low target. Statistical
analyses of right-footed penalty kicks taken in the
UK Premier League from 2005 to 2008 (Lovejoy &
Holmes, 2008) indicated that the largest percentage
of kicks were taken to the bottom left corner of the
goal, with 71% success compared with 100% success
for kicks aimed at the top right corner and 93%
success for the top left corner. However, the
muscular demands of shooting to various corners
of the goal are unknown.
Therefore, the aim of this study was to investigate
EMG muscle activity of three quadriceps muscles
during soccer kicking towards a high or a low target
on the right and left sides of a goal. We hypothesized
that there would be a significant difference in
quadriceps muscle activity when shooting at high
and low targets on left and right sides of the goal. We
also hypothesized that there would be significant
differences in peak muscular activity across each
phase of the kick. Finally, we hypothesized that there
would be no significant difference in the percentage
time at which peak EMG activity occurred in each
muscle when kicking towards the four targets.
Methods
Participants
Six male university-level competitive soccer players
with 10 years or more experience volunteered for this
study (mean +s: age 21.2 +0.1 years, body mass
73.0 +7.2 kg, height 1.77 +0.06 m). All partici-
pants were right-footed, physically active, and had no
history of lower limb, spinal or neurological injury.
Participants provided signed written informed con-
sent to partake and the institutional ethics committee
approved the study.
Procedures
All participants performed a 5 min dynamic stretch-
ing warm-up. To generate reference EMG data for
normalization purposes, each participant performed
three dynamic squat-jumps immediately before the
kicking protocol (Ball & Scurr, 2008). During the
squat-jumps, the participants crouched with their
feet shoulder-width apart, the back straight, and
thighs parallel to the ground. After familiarization
with the task, each participant performed maximum
squat-jumps. Following this, each participant per-
formed right-footed maximum velocity instep kicks
of a stationary ball from a marked penalty spot.
Three trials in four target conditions were under-
taken. Targets (0.75 m
2
) were positioned in the four
corners of a standard size soccer goal, 11 m from the
penalty spot. A ball of standard size and inflation was
used to perform the trials. Participants were asked to
hit the ball as hard and fast as possible, whilst
maintaining accuracy towards the target area. Parti-
cipants started their run-up from a marked point at
an angle of 308(Lees & Nolan, 1998). A rest period
of 1 min between kicks was provided and only kicks
placed in the target areas were counted.
During all conditions, EMG data were recorded at
1000 Hz and analysed using the Biometrics Datalog
(UK) system. Electromyographic recordings were
obtained from the vastus lateralis, vastus medialis,
and rectus femoris of the right leg. The centre of
each muscle belly was identified by palpation during
voluntary isometric efforts. Electrode location and
placement techniques were undertaken in accor-
dance with SENIAM (Surface Electromyography for
the Non-Invasive Assessment of Muscles) Group
recommendations. Electrode location sites were
prepared by shaving and cleansing, using an iso-
propyl alcohol swab (Medi-Swab, Seton Healthcare
Group, UK) to reduce skin impedance (10 kO).
Active Ag/AgCl bipolar pre-amplified disc electrodes
(SX230, Biometrics, UK; gain 61000; input
impedance 4100 MO; common mode rejection
ratio 496 dB; noise 51–2 mVRMS; bandwidth
20–450 Hz) with 1 cm separation distance were
adhered in-line with the muscle fibres, using
hypoallergenic adhesive tape (3M, UK). A passive
reference electrode (R300, Biometrics, UK) was
placed on the participant’s olecranon process.
All electrodes were connected to the Datalog,
which was securely attached to the participant’s
abdominal area during the task to minimize artifacts
due to hardware movement and to enable the
dynamic trials to be performed. The mass of the
Datalog (0.5 kg) was assumed to have a negligible
effect on kick performance. The Datalog used both a
high-pass third-order filter (18 dB/octave; 20 Hz) to
remove DC offsets due to membrane potential, and a
low-pass filter for frequencies above 450 Hz. The
electrodes contained an eighth-order elliptical filter
(760 dB at 550 Hz). An event marker (IS3,
Biometrics, UK) determined foot–ball contact and
ball–target contact. All EMG equipment was cali-
brated in accordance with the manufacturer’s guide-
lines.
Data analysis
Electromyography data were uploaded to a Toshiba
Laptop (Japan) and analysed using the Biometrics
Datalog Analysis Package Software (Version 5.02,
Biometrics, UK). The raw EMG signals (mV) were
visually checked for artifacts. Raw EMG was then
processed using root mean square (window length of
248 J. C. Scurr et al.
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20 ms) and peak values were identified and ex-
pressed as a percentage of the peak root mean square
EMG recorded during the squat-jumps. These
percentage EMG values and the time at which they
occurred (normalized to the percentage of total kick
duration) were established during three phases of the
kick: Phase 1 corresponded to the period when the
participant started their movement (EMG recording
initiated) until foot–ball contact (determined by the
event marker); Phase 2 was defined as the period
from foot–ball contact until ball–target contact
(determined by the event marker); Phase 3 was the
period from ball–target contact to the end of the
movement.
Statistical analysis
Each participant’s results were averaged across the
three trials for each muscle, target area, and phase of
the kick, then analysed using the statistical package
SPSS (v.15). All data were normally distributed
(Kolmogorov-Smirnoff and Shapiro-Wilk tests,
P40.05). A repeated-measures analysis of variance
(ANOVA) with two within-participant variables
(target, with 4 levels and phase, with 3 levels) and
one between-participant variable (muscle, with 3
levels) was applied to the normalized EMG data.
Mauchley’s test of sphericity showed that sphericity
was not assumed and therefore a correctional factor
was applied (Greenhouse-Geisser). Post-hoc paired
t-tests with a Bonferroni adjustment (P¼0.008)
were used to determine where significant differences
lay. Then, three repeated-measures ANOVAs (one
for each phase of the kick) with one within-
participant variable (target, with 4 levels) and one
between-participant variable (muscle, with 3 levels)
were used to compare the time at which peak EMG
activity occurred. Mauchley’s test of sphericity
showed that sphericity was assumed for these data.
For all statistical tests, partial eta-squared (Z
2
) values
were calculated to determine the effect size of the
statistical analysis, with 40.01 defining a small effect
size, 40.06 a moderate effect size, and 40.14 a large
effect size (Cohen, 1988). Statistical significance was
set at P50.05 except where a Bonferroni adjust-
ment was applied.
Results
Peak EMG values ranged from 57% in Phase 3 for
the rectus femoris when kicking to the bottom left of
the goal to 121% for the vastus lateralis in Phase 3
when kicking to the top right of the goal (Figure 1).
Across all target areas, the vastus lateralis demon-
strated a higher level of activation in Phase 1
compared with the other muscles. However, statis-
tical analysis revealed no significant interaction effect
in normalized EMG when accounting for target,
muscle, and phase. When examining the main
statistical effects, EMG activity displayed no sig-
nificant difference across the three muscles of the
quadriceps and no significant difference across each
phase of the kick. A significant main effect on EMG
activity was identified when kicking to different areas
of the goal (F
2,13
¼4.34, P¼0.02, partial Z
2
¼0.22).
Further analysis of the main effect of target showed
greater overall muscle activity in the quadriceps
when kicking to the top right of the goal. In addition,
significantly greater quadriceps activity was required
to kick the ball to the right side of the goal than the
left side (t
111
¼4.59, P50.01, partial Z
2
¼0.1).
There was no significant difference in quadriceps
activity when kicking to the top or bottom of the goal
(t
111
¼1.4, P¼0.16, partial Z
2
¼0.1).
Figure 1. The average timing and amplitude of peak normalized
EMG activity for three quadriceps muscles during three kicking
phases to each target area during soccer instep kicking (n¼6).
Quadriceps EMG during soccer kicking 249
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The mean total duration of the kicks was 1.2 s
(s¼0.2) with Phases 1, 2, and 3 lasting an average of
0.47 s (s¼0.12), 0.27 s (s¼0.09), and 0.5 s
(s¼0.19), respectively. The instant at which peak
EMG activity occurred in each phase showed no
significant difference across targets and across
muscles (Figure 1).
Discussion
The aim of this study was to investigate EMG muscle
activity of three quadriceps muscles during soccer
instep kicking towards four pre-defined targets. The
results provided support for the first hypothesis, as
there were significant differences in EMG activity
when kicking towards different targets, with kicks
directed towards the top right target demonstrating
greater overall quadriceps muscle activation. The
second hypothesis was rejected as there was no
significant difference in peak quadriceps activation
when compared across the phases of the kick. The
third hypothesis was accepted, as the time at which
peak EMG activity occurred showed no significant
difference across the three muscles and across the
four targets areas.
When averaged across all the targets, normalized
EMG values of 77% for the rectus femoris, 89% for
the vastus lateralis, and 83% for the vastus medialis
were identified during the contact phase of the kick.
These values are lower than previously reported at
similar time points of an instep kick: Do¨ rge et al.
(1999) reported 93.7% for rectus femoris activity and
101.6% for vastus lateralis activity, while Brophy
et al. (2007) reported 100% for the vastus medialis.
However, as Do¨ rge et al. (1999) and Brophy et al.
(2007) analysed maximum instep kicks, whereas
kicking accuracy was investigated in the present
study, it is unsurprising that our values are lower.
Differences in muscular activation patterns were
evident between targets. Kicks taken towards the
right targets demonstrated significantly higher acti-
vation levels than kicks taken towards the left targets.
Kicks towards the top right target demonstrated
greater quadriceps activation than kicks towards the
top and bottom left targets. Kicks towards the top
right target demonstrated a greater activation of the
vastus lateralis compared with the rectus femoris and
vastus medialis, with peak vastus lateralis and vastus
medialis activity occurring at similar times of each
phase. This recruitment strategy may provide a
positive contribution to the increased muscular
activation during contact, stabilizing the knee joint
during extension. This increase in muscular demand
on the quadriceps when kicking towards the top right
corner, coupled with the greater success rate of
penalty kicks to this area of the goal (Lovejoy &
Holmes, 2008), suggests that soccer penalty perfor-
mance may be improved by training the quadriceps,
with specific emphasis on the vastus lateralis and co-
activation of the vastus lateralis and vastus medialis.
Despite no significant difference in the activation
levels of the three quadriceps muscles, Figure 1
shows differences in quadriceps recruitment patterns
throughout the kick. Peak rectus femoris activity was
lower than peak vasti activity for most phases of the
kick. Due to the biarticular nature of the rectus
femoris, during a kicking action where the trunk is
positioned over the legs, the rectus femoris is less
dominant during knee extension as a consequence of
hip flexion (Brophy et al., 2007). Figure 1 shows
lower rectus femoris activity when kicking to the top
of the goal, it is suggested that this may be a product
of diminished rectus femoris responsibility as the
participant changes the positioning of the trunk over
the legs in Phase 2 in an attempt to accurately place
the ball.
The issue of crosstalk in dynamic EMG assess-
ment is recognized; however, previous research has
quantified individual quadriceps activation during
maximum instep kicking utilizing similar procedures
(De Proft et al., 1988; Do¨ rge et al., 1999; Manolo-
poulos et al., 2006). Other muscles around the hip,
knee, and ankle may also play an important role
when kicking towards different targets. Therefore,
future research would benefit from recording muscle
activity in the hip, knee, and ankle in comparison to
the activity of the knee extensors assessed in this
study to fully quantify the interactive effects of
muscular activation on the outcome of penalty kicks
towards differing targets. Future research may also
benefit from synchronized kinematic and EMG data
collection to identify changes in ball–foot contact
when kicking at different targets. Furthermore, since
all the participants in the present study were right-
foot dominant and the results found greater quad-
riceps activation for these players when kicking
towards the top right corner of the goal, future
research should investigate quadriceps recruitment
in left-footed soccer players. This study was a
preliminary investigation into an under-reported area
of soccer performance, the small sample size limits
the generalizability of the conclusions, and given the
variability of EMG measures further studies larger
greater sample sizes are required.
In conclusion, the results of this study demon-
strate a significant increase in EMG activation in the
vastus lateralis, rectus femoris, and vastus medialis
for kicks directed towards the top right target of the
goal compared with kicks towards the bottom and
left of the goal. This target condition demonstrated
higher peak activation of the vastus lateralis and co-
activation of the vastus medialis and vastus lateralis
muscles throughout the kick. It is suggested that this
may produce a rapid, but stabilized extension of the
250 J. C. Scurr et al.
Downloaded By: [University of Canberra] At: 02:56 18 January 2011
knee joint compared with kicks directed towards the
top left and the bottom corners of the goal. This
study provides baseline data for further investigation
into the changes in muscular recruitment patterns
during various kicking situations, including specific
target areas of the goal, across differing player
skill levels, at varying states of fatigue, and after
injury.
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