Grip socks improve slalom course performance and reduce in-shoe foot displacement of the forefoot in male and female sports players

Abstract

This study assessed whether grip socks reduce in-shoe foot motion and improve change of direction performance in team sports players and compared the effects between males and females. A sledge and pulley system confirmed the static coefficient of friction was increased in the grip socks (1.17) compared to the regular socks (0.60). Performance during a slalom course was faster in the grip socks compared to regular socks (p = .001). Yet, there was no difference in the utilised coefficient of friction between the shoe-floor interface during a side-cut and turn change of direction manoeuvre. Three-dimensional motion capture revealed the grip socks reduced in-shoe foot displacement during the braking phase, with greater effect during the sharper turn manoeuvre. The magnitude of natural foot spreading within the shoe was greater in the calcaneus region than the metatarsals which suggests in-shoe sliding may only occur at the forefoot. Males tended to have increased in-shoe displacement, which is associated with larger foot spreading due to their increased mass. Findings provide guidance for product developers to enhance the support inside the shoe at the forefoot, and change of direction performance.

Full text

Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=rjsp20
Journal of Sports Sciences
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/rjsp20
Grip socks improve slalom course performance
and reduce in-shoe foot displacement of the
forefoot in male and female sports players
Charlotte Apps, Laura Dawson, Billy Shering & Petros Siegkas
To cite this article: Charlotte Apps, Laura Dawson, Billy Shering & Petros Siegkas (2022):
Grip socks improve slalom course performance and reduce in-shoe foot displacement
of the forefoot in male and female sports players, Journal of Sports Sciences, DOI:
10.1080/02640414.2022.2080163
To link to this article: https://doi.org/10.1080/02640414.2022.2080163
© 2022 The Author(s). Published by Informa
UK Limited, trading as Taylor & Francis
Group.
Published online: 01 Jun 2022.
Submit your article to this journal
Article views: 12
View related articles
View Crossmark data

SPORTS MEDICINE AND BIOMECHANICS
Grip socks improve slalom course performance and reduce in-shoe foot displacement
of the forefoot in male and female sports players
Charlotte Apps
a
, Laura Dawson
a,b,c
, Billy Shering
a,d
and Petros Siegkas
a,d
a
SHAPE Research Group, School of Science and Technology, Nottingham Trent University, Nottingham, UK;
b
Faculty of Sport, Allied Health &
Performance Science, St Mary’s University, Twickenham, UK;
c
School of Health and Sports Sciences, University of Suffolk, Ipswich, UK;
d
School of
Engineering and Technology, Cyprus University of Technology, Limassol, Cyprus
ABSTRACT
This study assessed whether grip socks reduce in-shoe foot motion and improve change of direction
performance in team sports players and compared the eects between males and females. A sledge and
pulley system conrmed the static coecient of friction was increased in the grip socks (1.17) compared
to the regular socks (0.60). Performance during a slalom course was faster in the grip socks compared to
regular socks (p = .001). Yet, there was no dierence in the utilised coecient of friction between the
shoe-oor interface during a side-cut and turn change of direction manoeuvre. Three-dimensional
motion capture revealed the grip socks reduced in-shoe foot displacement during the braking phase,
with greater eect during the sharper turn manoeuvre. The magnitude of natural foot spreading within
the shoe was greater in the calcaneus region than the metatarsals which suggests in-shoe sliding may
only occur at the forefoot. Males tended to have increased in-shoe displacement, which is associated with
larger foot spreading due to their increased mass. Findings provide guidance for product developers to
enhance the support inside the shoe at the forefoot, and change of direction performance.
ARTICLE HISTORY
Accepted 27 April 2022
Keywords
Cutting; traction; agility; in-
shoe movement
1. Introduction
Rapid changes of direction, or cutting manoeuvres, are frequent
in team sports (e.g., Fox et al., 2014; Matthew & Delextrat, 2009;
Morgan et al., 2021). Enhanced capability to change direction
quickly enables players to create the space and time needed for
a shot, pass, or block that can inuence match performance.
Faster change of direction ability has discriminated higher divi-
sion versus lower division players (Sekulic et al., 2017) and iden-
tication of youth athletes who develop into elite players
(Forsman et al., 2016). Whole-body change of direction angles
varies both within and between sports. For example, elite youth
football players perform more direction changes that are less
than 90 degrees (Morgan et al., 2021), whereas netball players
are reported to have increased frequencies of sharper turns and
side-cuts (Darnell, 2008; Fox et al., 2014). However, there is
limited evidence that any certain type of cutting manoeuvre is
more benecial to performance outcomes than others (Fox et al.,
2014), thus interventions to improve change of direction ability
should assess both slight and severe cuts.
Athletic footwear technologies can enhance change of
direction performance. Outsoles enable this by increasing the
coecient of friction at the shoe-oor interface (e.g., Ismail
et al., 2021; Luo & Stefanyshyn, 2011), which is
a biomechanical determinant of change of direction perfor-
mance (Dos’ Santos et al., 2017). Players are also able to sub-
jectively perceive increased footwear traction and their
increased condence may trigger technique adaptations to
increase the horizontal ground reaction force impulse and
consequently agility (Morio & Herbaut, 2018; Starbuck et al.,
2016). Moreover, other footwear components such as the mid-
sole, collar height (Staco et al., 1996), laces (Myers et al., 2019)
and insoles (Apps et al., 2019) can increase foot stability inside
the shoe by limiting foot-shoe motion. Thus, the time for the
foot to decelerate in the shoe is reduced and time to change
direction may be faster. Socks are the interim contact area
between the f7oot and footwear and are a standard piece of
sports apparel. Previous research associates dierent sock
materials with an increased risk of blisters and plantar foot
discomfort (Bogerd et al., 2012; Van Tiggelen et al., 2009).
There is likely an optimal amount of friction between the sock-
shoe interface to limit in-shoe motion and enhance agility
performance and maintain comfort. Players from a range of
team sports report wearing grip socks, which contain materials
with increased frictional properties, such as rubber. Grip socks
are marketed to reduce in-shoe slipping, and enhance speed
and agility. Yet, despite their widespread use, it has not been
investigated whether grip socks inuence change of direction
performance or how they are subjectively perceived.
Previous research on the inuence of footwear friction
focuses mainly on male participants (Morio et al., 2017). The
dierent anatomy and physiology of females has been
reported to result in gender specic biomechanical and neuro-
muscular responses during cutting manoeuvres, which are
related to their increased risk of injury (Beaulieu et al., 2008;
Sigward & Powers, 2006). The anatomy of the female foot tends
to be relatively slimmer at the instep and shorter from the heel
CONTACT Charlotte Apps Charlotte.apps@ntu.ac.uk SHAPE Research Group, School of Science and Technology, Nottingham Trent University, 168 New Hall
Block, Nottingham, UK
JOURNAL OF SPORTS SCIENCES
https://doi.org/10.1080/02640414.2022.2080163
© 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/),
which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.

to the outside ball of the foot, which should be considered for
shoe design (Wunderlich & Cavanagh, 2001). While certain
companies do manufacture female specic footwear for team
sports (e.g., Idasports), generally it is not clear if female shoes
are based upon a female specic last. Moreover, industry
response to the scientic knowledge that females require dif-
ferent sports shoes has lagged behind (Altho & Hennig, 2014;
Kulessa et al., 2017) and anecdotal evidence suggests that
female football players often wear male boots. Sex specic
adaptations to in-shoe frictional properties have not been
investigated. We postulated that the slender instep of the
female foot (Wunderlich & Cavanagh, 2001) would result in
increased in-shoe motion due to there being more space within
the shoe. Grip socks may therefore have an increased perfor-
mance benet in female sports players.
Therefore, the primary aim of this study was to assess if grip
socks reduce in-shoe foot motion and improve change of direc-
tion performance in team sports players. The secondary aim
was to compare the response between male and female
participants.
2. Materials and methods
Due to the lack of prior investigation, our assessments included
mechanical, biomechanical, performance and subjective per-
ception testing. This provided a comprehensive exploratory
evaluation of the functional eect of grip socks (Sterzing
et al., 2012).
2. 1 Socks and footwear
Two sock conditions were tested, grip socks (GS) and regular
sport socks (RS). The RS (Performance Crew Sports Socks,
Adidas) were 1.2 mm thick and material consisted of 60%
cotton, 36% polyester, 3% elastane and 1% nylon (Figure 1a).
The GS (LUX Sports) were 2.4 mm thick and had rubber pads (7
x 9 mm) on the inside and outside of the sock material
(Figure 1b). The haptic sensation of the nodules was immedi-
ately detectable which meant it was not possible to blind the
participants to the sock condition they were wearing. To con-
trol for the inuence of dierent types of shoes, participants
were provided with a standardised indoor football shoe
(Lunargato II, Nike; Figures 1(c,d) in each size from UK 6–11. It
is assumed that this is a unisex model, despite no smaller size
being commercially available. A practical approach was used to
ensure the t of the shoe because the football shoe tended to
t too small based on foot length measurement. Participants
tried on their usual sports shoe size, and if they believed the t
was correct the investigator checked there was one nger
width between the end of the shoe and the longest toe
(Blazer et al., 2018).
2. 2 Mechanical coecient of friction
To conrm the GS had increased frictional properties compared
to the regular sock a sledge and pulley system was used to test
the sock-insole interface and obtain the coecient of friction
(Figure 2). The system was tted on a Shimadzu (Nakagyo-ku,
Kyoto, Japan) AG-XD plus (part no. 337–01122-21, 50KN frame)
screw driven mechanical testing machine using a 1KN (Class 1)
load cell. The sledge was pulled horizontally at a constant
velocity (1.5 mm/min) using a steel wire (Ø = 1.2 mm). The
wire connected the sledge to the load cell and machine cross-
head through a pulley at a 90° angle. The insole was attached to
a stationary bottom plate and the sock specimens were
attached to the sledge. Mass was added to the sledge (~
2.5 Kg). The peak force prior to sliding was recorded and used
for calculating the static coecient of friction. Two dierent
sock specimens of each type (i.e. 2x grip sock and 2x regular
sock) were tested. Each test was repeated three times. The
apparatus was validated using a polyimide lm-lm interface
that was tested using two dierent methods i.e. the sledge and
Figure 1. The regular sock (a). the grip sock (b). the indoor football shoe (c and d) with markers attached to the shoe midsole: posterior lateral (spl), anterior lateral (sal),
anterior medial (sam), posterior medial (spm). Foot marker locations: first metatarsal head (mh1), first metatarsal base (mb1), fifth metatarsal head (mh5), fifth
metatarsal base (mb5), lateral calcaneus (lc), and medial calcaneus (mc).
2C. APPS ET AL.

pulley setup described above, and also tested by using an
inclined plane and a digital inclinometer for measuring the
angle of slippage, to ensure agreement and consistency in
the resulting coecient of friction.
2.2 Participants
Twenty recreational team sports players (10 males, 10 females;
age 21.7 (SD 2.4); height 170 cm (SD 8.3); body mass 76.8 kg (SD
17.2)) were recruited to participate in this study. All participants
had regularly played sport for at least 2 years, playing 3 times
a week on average (SD 1.3). Participant inclusion required the
absence of serious musculoskeletal injury in the six months
preceding testing. The study protocol received ethical approval
from the Human Invasive Research Ethics Committee at
Nottingham Trent University (application #637), and all partici-
pants gave written informed consent prior to testing.
The protocol consisted of two separate measurement ses-
sions: one for biomechanical measurements, and one for agility
performance and subjective perception.
2.3 Biomechanics
Participants completed a 10-minute warm-up including
dynamic stretches and a familiarisation to the cutting man-
oeuvres in their own footwear and then several practices in
each of the sock condition with the standardised shoe.
Following this, participants completed ve maximal eort 45°
side-cuts and ve 180° turns in each sock condition. This
allowed us to investigate the inuence of the GS in both a fast-
paced, slight (45°) and slower, severe (180°) change of direction
applicable to team sports (Bloomeld et al., 2007; Darnell, 2008;
Robinson et al., 2011). A trial was repeated if the change of
direction step was not completed with the dominant foot land-
ing on the force plate or if there was any noticeable targeting.
To ensure the correct degree of the side-cut were achieved,
cones were placed 1 metre away at 45° from the centre of the
force plate. The order of sock type and change of direction
angle was mixed between each participant. Timing gates
(Brower Timing Systems, Draper, UT, USA) monitored approach
speed (Figure 3). Participants were instructed to fasten the
Figure 2. Schematic representation of the apparatus for comparing the coefficient of friction between grip sock and regular sock specimens. The insole was fixated to
the aluminium plate. The sock specimen with sledge attachment were pulled along the insole.
Figure 3. Change of direction tasks for biomechanical measurements. (a) 45° side-cut through cones; (b) 180° complete turn.
JOURNAL OF SPORTS SCIENCES 3

shoes to their preferred tightness before the rst trial, the laces
were then marked through the top eyelets. To ensure the
support provided by the upper remained consistent across
sock conditions participants were required to ensure the
marks were just visible through the top eyelets for all trials.
To limit the inuence of fatigue, there was a 1-minute rest
between trials.
A force plate (0.4 m x 0.6 m, Kistler, Winterhur, Switzerland),
sampling at 1000 Hz recorded ground reaction forces during
the change of direction step. Eight Miqus motion capture cam-
eras (Qualisys, Gothenburg, Sweden) were used to measure the
displacement of the markers placed on the foot relative to the
markers placed on the shoe during foot ground contact. The
cameras were placed around the force plate, approximately
1 m from the centre, sampling at 200 Hz. The capture volume
was calibrated across the length and width of the force plate,
and 0.5 m above the surface. Calibration was accepted when
the residual camera errors were <0.3 mm, allowing sub-
millimetre accuracy. Four reective markers were attached to
the shoe midsole at the anterior and posterior of the lateral and
medial border (Figure 1). Holes were cut on the shoe-upper and
sock on the dominant foot for the attachment of six reective
markers (12 mm Ø) directly onto the foot (Figure 1). To limit
interference from movement of the shoe upper, holes were
25 mm in diameter (Bishop et al., 2015). The marker locations
enabled assessment of regional foot displacement which varies
between cutting manoeuvres (Apps et al., 2019).
Marker data was digitised in Qualisys Track Manager
(Qualisys, Gothenburg, Sweden) and exported to Visual 3D
(C-Motion, Rockville, MD, USA) for further analysis. A fourth
order bi-directional Butterworth lter with 20 Hz and 50 Hz
frequency cut-o frequency were applied to the marker co-
ordinate and analogue force plate channels, respectively.
The initial touchdown and toe-o events of the change of
direction step were determined by a 10 N threshold of the
vertical ground reaction force and estimated ground contact
time. The utilised coecient of friction (uCOF) between the
shoe-oor was calculated as the ratio of the resultant horizontal
forces to vertical force (Morio et al., 2017). The mean uCOF
during the braking phase and propulsive phase were com-
puted, according to Apps et al., (2019), to avoid artefacts by
dividing by low vertical forces (Luo & Stefanyshyn, 2011). The
braking phase was dened from two frames after initial touch-
down and ended at 50% of ground contact time. The propul-
sive phase started at the end of the braking phase and ended
two frames prior to toe-o. The resultant horizontal impulse
was computed to indicate changes in the magnitude of the
shear forces between sock conditions and sex.
To calculate in-shoe foot displacement, the three-
dimensional distance between the following lateral foot mar-
kers and shoe landmarks were computed:
●The fth-metatarsal head and the midpoint between the
anterior-lateral and anterior-medial shoe markers.
●The fth metatarsal base and the midpoint of the anterior
and posterior shoe markers.
●The lateral calcaneus and the midpoint between the pos-
terior-lateral and posterior-medial shoe markers.
These shoe landmark locations were selected due to their
closer proximity of the foot markers, thus limiting changes to
foot-shoe displacement due to inter-segmental foot motion.
Each foot-shoe distance at the start of the braking phase was
subtracted to set the initial value to zero. In-shoe foot motion
between the lateral foot markers and shoe were determined by
the range of displacement during the braking and propulsive
phase. This was to correspond with the uCOF and determine
during which phases of the change of direction GS may inu-
ence performance. To give indication of the level of in-shoe
foot motion, which is caused by natural foot spreading (Morio
et al., 2009) the range of displacement in the three-dimensional
distance between the markers on the metatarsal heads, meta-
tarsal bases and medial and lateral calcaneus were computed.
2.4 Slalom performance and subjective perception
All participants completed a 26 m slalom course, previously
used to evaluate actual and perceived performance with vary-
ing footwear and surfaces (Sterzing et al., 2009). The slalom
incorporates 12 accelerations with 10 cutting movements and 1
complete turn. Prior to testing there was a 10-minute warm up
including: 2 sub-maximal familiarisation trials in participants’
own footwear and an additional sub-maximal and maximal
familiarisation trial in each sock condition. Following this,
three maximal eort trials in GS and RS were recorded. After
each trial, the sock condition was alternated during
a mandatory 3-minute recovery period to limit the inuence
of fatigue.
A pair of timing gates (Brower Timing Systems, Draper, UT,
USA) were placed where the course both started and nished
to evaluate performance. After each maximal trial subjective
perception of speed and in-shoe grip was measured using
150 mm visual analogue scales (VAS), anchored with the
terms “very slow” to “very fast” and “very low” to “very high”,
respectively (Apps et al., 2019). Following a further submaximal
trial in each sock condition, subjective perception of comfort
and stability were measured using VAS, with the terms “very
uncomfortable” to “very comfortable” and “very unstable” to
“very stable”. This method of assessing perception of footwear
comfort has been proven reliable in previous research (Mills
et al., 2010).
2.6 Statistics
For each participant, parameter mean values were com-
puted across trials for each sock condition. Statistical analy-
sis was performed in SPSS software (SPSS v26, SPSS Inc.,
Chicago, IL, USA). Normality of parameters were checked
with the Shapiro-Wilk test and visually checked with box-
plots (Ghasemi & Zahediasl, 2012) to identify deviations
from normality and detect outliers. Parameters met para-
metric test assumptions. Two-way mixed ANOVA tests
assessed the main eect within participants (socks: regular
vs grip) and between participant groups (sex: male vs
female) for biomechanics, performance and subjective per-
ception results. The alpha level was set at 0.05, there was
no adjustment for the large number of comparisons due to
the nature of this research being explorative. To indicate
4C. APPS ET AL.

the relevance of ndings, eect sizes (η
2
) were calculated
for the main eects. A strong eect size was dened by
η
2
> 0.5, moderate between 0.5 and 0.3 and low < 0.3
(Field, 2015). Signicant interactions were followed up with
paired t-tests to indicate sock specic eects in males and
females. Paired t-tests conrmed there was no dierence
approach speed between sock conditions during side-cuts
(p = .630) or turns (p = .872) and was subsequently not
considered as a covariate for foot-displacement and foot-
spreading results.
2. Results
Mechanical coecient of friction
The coecient of friction obtained by the mechanical tests
appeared consistent (Table 1). The GS-insole interface resulted
in nearly double the coecient of friction to that of the RS-
insole interface.
Biomechanics
The was only one signicant interaction across biomechanical
results, indicating the GS had similar eect across both sexes.
Ground reaction forces
There were no signicant dierences between sock conditions
in the horizontal ground reaction force impulse, uCOF or con-
tact time for either change of direction tasks (Table 2). There
was a signicant main eect of sex in the horizontal ground
reaction force impulse, whereby males had increased impulses
during both manoeuvres in the braking phase and propulsive
phase. The uCOF results revealed no signicant dierence
between males and females.
In-shoe foot displacement
During the braking phase for both change of direction
manoeuvres, the GS signicantly reduced in-shoe foot dis-
placement across foot locations compared to RS, except at
the fth metatarsal head in the side-cut (Table 3). Females
had signicantly reduced in-shoe foot displacement com-
pared to males during the braking phase at the fth meta-
tarsal base across manoeuvres, and in the lateral calcaneus
in the turn.
During the propulsive phase, there were fewer signicant
results. There was signicantly reduced in-shoe displacement at
the lateral calcaneus in GS compared to RS in the side-cut and
the turn. In the turn at the lateral calcaneus there was signi-
cantly reduced in-shoe displacement in females compared to
males.
Foot spreading
The foot spreading results are reported in Table 4. In two
participants (1 male and 1 female) there were missing data for
the calcaneus spreading during turns due to the medial calca-
neus marker being obscured by shoe. There appeared to be
a greater eect of sex, than sock condition, with males tending
to have increased foot spreading. Yet there were fewer signi-
cant results than the in-shoe foot displacement results.
During the braking phase there was reduced foot spreading
at the calcaneus in females compared to males during the side-
cut and turn. In the turn there was also signicantly reduced
foot spreading in females compared to males at the metatarsal
bases during the braking and propulsive phase. The only sig-
nicantly dierence between sock conditions was the reduced
calcaneus spreading in GS compared to RS during the braking
phase of the turns.
In the side-cut during the propulsive phase there was
a signicant interaction in the calcaneus. Follow-up paired
t-tests results revealed signicantly reduced spreading in GS
compared to RS in females (p = .042) and a tendency to
increase in males (p = .075).
Slalom performance and subjective perception
Regardless of sex, there was a signicant main eect for sock
condition (p = .001), with faster times in GS compared to RS
(Table 5). There was no signicant main eect of sex, with
similar times achieved between males and females (p = .429).
There was no signicant interaction eect on the type of sock
worn between males and females in the time to complete the
slalom course (p = .711).
There were signicant interactions of the subjective scores for
speed, in-shoe grip and stability, but not comfort. Figure 4 illus-
trates this was due to females rating RS relatively lower and GS
relatively higher than males. Follow-up paired tests revealed
females perceived their speed to be signicantly faster in GS
(p = .003), but no eect in males (p = .121). In-shoe grip and
stability were signicantly increased in GS compared to RS in both
males (grip: p = .011; stability: p < .001) and females (grip: p = .001;
stability: p < .001). Comfort perception was signicantly increased
in GS compared to RS, but there was no eect between sexes.
3. Discussion
In relation to the primary aim of this study, the commercially
available grip socks (GS) tested did improve change of direction
performance during a slalom course compared to a regular
sock (RS). On average, female and male participants completed
the course in 12.74 and 12.57 seconds in GS compared to 13.29
and 12.89 seconds in RS respectively, which was a moderate
eect (Table 5). However, there was no dierence in the
approach speeds, contact time and horizontal ground reaction
forces during the side-cut and turn tasks. Participants may have
adapted to the dierent friction at the sock-shoe interface
during a single change of direction, but any technique altera-
tions were not sucient to maintain performance over multiple
cuts. Alternatively, slight biomechanical modications that
were not detected in our cutting results may accumulate over
the multiple changes of directions in the slalom course.
Table 1. Calculated coefficient of friction for grip (gs) and regular socks (rs). Two
specimens of each type were tested.
Sock type Specimen COF (SD) Average COF
RS 1 0.55 (0.023) 0.6
2 0.65 (0.045)
GS 1 1.2 (0.041) 1.17
2 1.13 (0.109)
JOURNAL OF SPORTS SCIENCES 5

To investigate the mechanism of how GS aect change of
direction ability we assessed the mechanical coecient of fric-
tion, and in-vivo measurements of in-shoe displacement using
motion capture and ground reaction forces. Mechanical mea-
surements revealed GS nearly doubled the coecient of fric-
tion, compared to RS (Table 1). The embedded polymer
components, within the GS fabric, appeared to be slightly
protruding which may result in partial enveloping by the insole
hence increasing the eective interface resistance to slippage.
Due to this, a variation to the ASTM D1894 standard test was
used that had a lower velocity and increased weight, which
were intended to reveal any relevant enveloping mechanisms
due to the dierent stiness of the GS nodules, whilst reducing
inertial eects. The increased mechanical coecient of friction
in GS corresponded with a reduction of in-shoe foot displace-
ment during the braking phase of the change of directions
manoeuvres (Table 3). However, as mentioned the reduced in-
shoe foot motion in the GS did not improve performance
during the side-cut or turn. We speculate reduced in-shoe
movement and better foot stability in the GS resulted in
improved slalom course performance, but further research is
warranted to substantiate this claim. In the side-cuts, the abso-
lute dierence in in-shoe foot displacement between socks at
the lateral calcaneus and fth metatarsal base was less than
1 mm in males. The small eect size and accuracy of the motion
capture system up to 0.3 mm suggest this is not a meaningful
dierence. In the sharper turn manoeuvre, GS reduced in-shoe
foot displacement to a greater extent; between 1.3–2.8 mm
across sexes and foot locations (Table 3). This is related to the
increased horizontal shear forces and uCOF in the turn com-
pared to side-cut (Table 2). These results are similar to Apps
et al., (2019), who reported an insole with increased mechanical
friction was associated with reductions of in-shoe foot displa-
cement in a complete turn during braking, but not a side-cut.
During the initial braking phase of a cut, uCOF is increased and
dependent of the movement dynamics upon landing
(C. Y. M. Morio et al., 2015). Landing with a forefoot strike during
cuts increases ankle work (Donnelly et al., 2017), shear forces
and potentially subsequent in-shoe motion at the forefoot. We
did not assess foot strike pattern in this study and future
research is warranted to assess the eect on in-shoe motion.
Our secondary aim was to compare the response between
male and female participants. Given females tend to have nar-
rower feet we speculated females may have increased in-shoe
foot displacement in the shoe last designed for male feet, and
therefore GS may have greater eect to their agility performance.
However, there was no dierence to performance between
males and females, shown by the lack of signicant interaction
result on the slalom course. Thus, performance advantage of
wearing grip socks seems to work equally for both sexes.
Table 2. Mean (sd) ground reaction force parameters during the side-cut and turn as a function of sock condition and sex.
Cut
Females Males
Effect SizeRS GS RS GS
Contact time (s) Side-cut .209 (.025) .209 (.031) .214 (.030) .224 (.034)
Turn .474 (.088) 0.479 (.098) .539 (.070) .546 (.079)
Horizontal GRF impulse braking phase (N.s) Side-cut 57.0 (7.7) 56.0 (8.9) 65.6 (4.7) 66.8 (8.8)
#
.34
Turn 115.5 (16.5) 121.1 (13.3) 152.7 (22.7) 146.9 (26.5)
#
.42
Horizontal GRF impulse propulsive phase (N.s) Side-cut 33.60 (3.8) 34.7 (5.6) 43.0 (7.0) 41.4 (6.2)
#
.43
Turn 93.8 (15.2) 93.4 (10.6) 130.3 (22.0) 127.9 (27.1)
#
.50
uCOF braking phase Side-cut .415 (.041) .406 (.037) .395 (.058) .383 (.046)
Turn .578 (.063) .591 (.067) .590 (.062) .577 (.063)
uCOF propulsive phase Side-cut .527 (.038) .538 (.034) .510 (.032) .500 (.054)
Turn .588 (.057) .605 (.064) .615 (.048) .603 (.047)
GRF = ground reaction force. uCOF = utilised coefficient of friction. RS = regular sock, GS = Grip sock. Significant results (p < .05): * = main effect of SOCK,
#
= main
effect of SEX,
$
interaction.
Table 3. Mean (sd) range of in-shoe foot displacement (mm) of the fifth metatarsal head, fifth metatarsal base and lateral calcaneus during the braking and propulsive
phases of the side-cut and turn as a function of sock condition and sex.
Cut, phase Foot location
Females Males
Effect SizeRS GS RS GS
Side-cut, braking Metatarsal head 5 5.2 (3.1) 5.2 (2.2) 4.8 (1.9) 4.7 (1.9)
Metatarsal base 5 4.8 (2.3) 3.7 (1.3) 6.4 (2.3) 5.6 (1.6) *.25,
#.
22
Lateral calcaneus 4.7 (2.7) 2.8 (1.1) 5.5 (1.7) 5.1 (1.8) *.27
Turn, braking Metatarsal head 5 9.9 (3.0) 8.6 (2.4) 12.2 (4.8) 10.8 (2.2) *.27
Metatarsal base 5 8.9 (2.6) 6.4 (2.2) 11.4 (2.3) 9.2 (1.4) *.71,
#
.33
Lateral calcaneus 6.6 (3.6) 3.8 (1.3) 8.4 (1.8) 6.2 (2.0) *.55,
#
.24
Side-cut, propulsive Metatarsal head 5 4.4 (1.8) 5.5 (2.2) 4.3 (1.6) 4.3 (2.5)
Metatarsal base 5 3.1 (1.6) 3.4 (1.6) 3.6 (2.0) 3.8 (1.9)
Lateral calcaneus 4.1 (1.6) 2.5 (1.1) 3.8 (1.1) 3.6 (1.4) *.22
Turn, propulsive Metatarsal head 5 5.9 (1.3) 6.1 (1.8) 6.3 (2.2) 6.7 (2.5)
Metatarsal base 5 4.9 (2.3) 4.8 (1.6) 5.5 (1.6) 5.2 (1.3)
Lateral calcaneus 3.1 (1.2) 2.2 (1.0) 4.0 (1.6) 3.4 (0.7) *.34,
#
.24
Significant results (p < .05): * = main effect of SOCK,
#
= main effect of SEX,
$
interaction. RS = regular sock, GS = Grip sock.
6C. APPS ET AL.

Results further confound this theory because males actually had
increased in-shoe displacement during the braking phase at the
fth metatarsal base in both cuts, and the lateral calcaneus in the
turn during the braking and propulsive phase (Table 3). The
movement dynamics of the male participants resulted in an
increased horizontal force impulse (Table 2), which may be asso-
ciated with their increased mass. Yet there was similar utilised
coecient of friction (uCOF) between the sexes, suggesting
males must have also applied an increased normal force.
Having an increased horizontal force requires a sucient
increase in normal force so that the uCOF does not exceed the
mechanically available friction and result in slippage. Although
we did not measure the in-shoe forces, the similar ratio of
horizontal to vertical ground reaction force between the shoe-
oor interface suggests the higher momentum in males is not
associated with the increased in-shoe foot displacement. Female
participants were able to perceive the inuence of the grip socks
on their speed, whereas the males did not (Figure 4). This may
give females a psychological advantage whilst wearing grip
socks, but this did not result in an increased uCOF or perfor-
mance during the side-cut and turn task. Thus, a sex eect of GS
on performance is not supported by our ndings.
Natural foot motion causes the foot to expand, even when
restricted by footwear (Morio et al., 2009). Previous research
investigating in-shoe motion has not accounted for foot
spreading contributing to foot-shoe displacement results.
Therefore, we estimated foot spreading by calculating the dis-
placement of the foot markers on the metatarsal heads, meta-
tarsal bases and the calcaneus. The male foot tended to expand
to a greater extent than the female foot (Table 4). This suggests
the increased in-shoe foot displacement results in males are in
fact caused by larger foot spreading, particularly at the meta-
tarsal base and lateral calcaneus during braking for the turn
where both results were signicantly greater in males (Tables 3
and 4). A normalisation method to account for foot size when
calculating in-shoe foot displacement should be considered in
the future work to limit this issue. Interestingly, some foot
spreading results were greater than the in-shoe foot displace-
ment which would suggest there might not be any foot sliding.
Particularly, the calcaneus foot spreading results were all
greater than the lateral calcaneus in-shoe displacement. The
heel fat pad deforms to cushion impacts upon landing, and
although the extent during cutting manoeuvres is unknown, it
was reported to deform 35% in shod running (Aerts & De
Table 4. Mean (sd) range of foot spreading (mm) of the metatarsal heads, metatarsal bases and calcaneus during the braking and propulsive phases of the side-cut and
turn as a function of sock condition and sex.
Cut, phase Foot location
Females Males
Effect SizeRegular Grip Regular Grip
Side-cut,
braking
Metatarsal heads 3.6 (1.6) 4.1 (1.5) 5.2 (2.6) 5.5 (2.0)
Metatarsal bases 3.3 (1.4) 3.5 (1.2) 4.8 (1.7) 6.1 (3.2)
Calcaneus 5.7 (2.4) 4.2 (1.1) 6.6 (2.2) 7.1 (3.0)
#
.22
Turn,
braking
Metatarsal heads 5.1 (1.4) 5.8 (1.2) 7.5 (3.1) 6.7 (2.8)
Metatarsal bases 5.0 (2.6) 4.1 (1.7) 8.1 (3.1) 8.3 (4.9)
#
.28
Calcaneus 8.3 (2.1) 5.7 (1.7) 13.0 (1.9) 9.5 (2.9) *.64,
#
.64
Side-cut,
Propulsive
Metatarsal heads 4.2 (1.9) 5.1 (2.3) 5.1 (3.2) 5.9 (3.5)
Metatarsal bases 4.0 (1.4) 3.6 (1.4) 5.5 (2.9) 5.6 (4.1)
Calcaneus 7.2 (2.7) 6.1 (1.8) 6.5 (1.5) 8.4 (2.3)
$
.38
Turn,
propulsive
Metatarsal heads 4.7 (1.9) 5.4 (1.2) 5.4 (3.2) 6.0 (3.1)
Metatarsal bases 3.9 (1.7) 3.5 (0.8) 5.4 (2.4) 4.9 (1.7)
#
.20
Calcaneus 5.5 (1.1) 5.6 (1.2) 7.6 (3.0) 6.9 (2.7)
Significant results (p < .05): * = main effect of SOCK,
#
= main effect of SEX,
$
interaction
Figure 4. Mean (sd) subjective perception scores across sock conditions and sexes. Significant results indicated: * = main effect of sock,
#
= main effect of sex,
$
interaction.
JOURNAL OF SPORTS SCIENCES 7

Clercq, 1993). When taking foot spreading results into account,
only the forefoot in the turn manoeuvre has greater in-shoe
foot displacement results. Thus, agility performance gains due
to in-shoe movement may only occur in the forefoot region
where there is less support from the shoe upper during sharp
changes of direction.
The grip socks were perceived to increase comfort, stability
and in-shoe grip (Figure 4). This suggests that the increased
frictional properties of GS did not increase the plantar pres-
sures and shear forces that are associated with foot discom-
fort and blisters (Castro et al., 2013; Knapik et al., 1996). It is
acknowledged that the lack of blinding to the sock condition
because of the rubber nodules on GS would very likely have
aected the subjective perception scores (Matthias et al.,
2021) and potentially the performance in the slalom course.
However, players can feel the haptic sensation of socks in the
real-world sporting environment and articially removing this
would reduce the external validity of this research. Moreover,
the perception of stability and in-shoe grip may have impor-
tant implications for reducing sports injuries. Shinohara and
Gribble (2013), assessed the eects of ve-toed socks with
rubber grip on the foot sole on static postural control in
healthy young adults. They reported an improvement of static
postural control, highlighting that one of the contributing
factors was the increased traction due to the GS increasing
proprioception. Whether this has an applied eect during
dynamic change of directions in team sports is unknown
and warrants investigation.
This study had limitations which should be considered when
interpreting ndings. Firstly, the high impact upon landings
during the change of directions causes marker artefacts due to
oscillations relative to the skin. The lter applied and analysis
was from 2 frames after initial touchdown to limit this eect.
Despite there being less inuence of wobbling mass on the foot,
this artefact cannot be avoided with 3D motion capture (Kessler
et al., 2019). Secondly, the GS were thicker than the RS (2.4 vs
1.2 mm), which may have aected the subjective rating, such as
comfort and stability. The thicker GS would likely have reduced
the space inside the shoe, but we do not believe this confounds
the in-shoe foot displacement results because the cotton mate-
rial was very compliant and deforms easily. Thirdly, although the
sample size between sock conditions (n = 20) was similar to past
studies, the sample size for the sex comparison (n = 10) was
smaller. Lastly, it is acknowledged there were numerous statis-
tical tests conducted in this study due to its explorative
approach. This increased the risk of type 1 errors in the ndings.
In conclusion, the grip socks tested improved agility per-
formance across male and female participants and can be
recommended to team sports players to enhance their
change of direction ability. This is attributed to the increased
mechanical coecient of friction of GS reducing in-shoe foot
displacement of the forefoot during the deceleration of the
sharper turn manoeuvre and not shoe-oor ground reaction
forces. The in-shoe motion results calculated in this study
and past research are obscured by the natural foot spread-
ing during cutting manoeuvres. The calcaneus foot spread-
ing was greater than the relative in-shoe displacement,
suggesting the commercial indoor football shoe provides
adequate support to prevent in-shoe movement in the rear-
foot. Future work should follow-up ndings of perceived in-
shoe grip, stability and comfort enhancement in grip socks
by assessing balance and injury risk benets.
Disclosure statement
No potential conict of interest was reported by the author(s).
Funding
This study received no external funding or had any involvement from LUX
Sports or any other company.
ORCID
Charlotte Apps http://orcid.org/0000-0002-7354-0003
Laura Dawson http://orcid.org/0000-0003-4884-7748
Petros Siegkas http://orcid.org/0000-0001-9528-2247
References
Aerts, P., & De Clercq, D. (1993). Deformation characteristics of the heel
region of the shod foot during a simulated heel strike: The eect of
varying midsole hardness. Journal of Sports Sciences, 11(5), 449–461.
https://doi.org/10.1080/02640419308730011
Altho, K., & Hennig, E. M. (2014). Criteria for gender-specic soccer shoe
development. Footwear Science, 6(2), 89–96. https://doi.org/10.1080/
19424280.2014.890671
Apps, C., Rodrigues, P., Isherwood, J., & Lake, M. (2020). Footwear insoles
with higher frictional properties enhance performance by reducing
in-shoe sliding during rapid changes of direction. Journal of Sports
Sciences, 38(2), 206–213. https://doi.org/10.1080/02640414.2019.
1690618
Beaulieu, M. L., Lamontagne, M., & Xu, L. (2008). Gender dierences in
time-frequency EMG analysis of unanticipated cutting maneuvers.
Medicine and Science in Sports and Exercise, 40(10), 1795–1804. https://
doi.org/10.1249/MSS.0b013e31817b8e9e
Bishop, C., Arnold, J. B., Fraysse, F., & Thewlis, D. (2015). A method to
investigate the eect of shoe-hole size on surface marker movement
when describing in-shoe joint kinematics using a multi-segment foot
model. Gait & Posture, 41(1), 295–299. https://doi.org/10.1016/j.gaitpost.
2014.09.002
Blazer, M. M., Jamrog, L. B., & Schnack, L. L. (2018). Does the shoe t?
Considerations for proper shoe tting. Orthopaedic Nursing, 37(3), 169–174.
Bloomeld, J., Polman, R., & O’Donoghue, P. (2007). Physical demands of
dierent positions in FA premier league soccer. Journal of Sports Science
& Medicine, 6(1), 63. https://www.ncbi.nlm.nih.gov/pmc/articles/
PMC3778701/
Bogerd, C. P., Niedermann, R., Brühwiler, P. A., & Rossi, R. M. (2012). The
eect of two sock fabrics on perception and physiological parameters
associated with blister incidence: A eld study. Annals of Occupational
Hygiene, 56(4), 481–488. https://doi.org/10.1093/annhyg/mer127
Castro, M., Abreu, S., Sousa, H., Machado, L., Santos, R., & Vilas-Boas, J. P.
(2013). Ground reaction forces and plantar pressure distribution during
occasional loaded gait. Applied Ergonomics, 44(3), 503–509. https://doi.
org/10.1016/j.apergo.2012.10.016
Table 5. Mean (sd) slalom course performance times (seconds).
Females Males
Effect SizeRegular Grip Regular Grip
13.29 (1.10) 12.74 (.81) 12.89 (0.99) 12.57 (0.89) *.49
Significant results (p < .05): * = main effect of SOCK,
#
= main effect of SEX,
$
interaction
8C. APPS ET AL.

Darnell, E. (2008). Injury risk during netball competition: an observational
investigation (Doctoral dissertation, University of Wales Institute Cardi).
Donnelly, C. J., Chinnasee, C., Weir, G., Sasimontonkul, S., & Alderson, J.
(2017). Joint dynamics of rear-and fore-foot unplanned sidestepping.
Journal of Science and Medicine in Sport, 20(1), 32–37. https://doi.org/10.
1016/j.jsams.2016.06.002
Dos’ Santos, T., Thomas, C., Jones, P. A., & Comfort, P. (2017). Mechanical
determinants of faster change of direction speed performance in male
athletes. Journal of Strength and Conditioning Research, 31(3), 696–705.
https://doi.org/10.1519/JSC.0000000000001535
Field, A. (2015). Discovering statistics using IBM SPSS statistics (5th ed.). Sage.
Forsman, H., Blomqvist, M., Davids, K., Liukkonen, J., & Konttinen, N. (2016).
Identifying technical, physiological, tactical and psychological character-
istics that contribute to career progression in soccer. International
Journal of Sports Science & Coaching, 11(4), 505–513. https://doi.org/10.
1177/1747954116655051
Fox, A., Spittle, M., Otago, L., & Saunders, N. (2014). Oensive agility tech-
niques performed during international netball competition.
International Journal of Sports Science & Coaching, 9(3), 543–552.
https://doi.org/10.1260/1747-9541.9.3.543
Ghasemi, A., & Zahediasl, S. (2012). Normality tests for statistical analysis:
A guide for non-statisticians. Journal of Endocrinology and Metabolism,
10(2), 486–489. https://doi.org/10.5812/ijem.3505
Ismail, S. I., Nunome, H., & Tamura, Y. (2021). Does visual representation of
futsal shoes outsole tread groove design resemblance its mechanical
traction, dynamic human traction performance, and perceived traction
during change of direction and straight sprint tasks? Footwear Science,
13(1), 79–89. https://doi.org/10.1080/19424280.2020.1825534
Kessler, S. E., Rainbow, M. J., Lichtwark, G. A., Cresswell, A. G., D’Andrea, S. E.,
Konow, N., & Kelly, L. A. (2019). A direct comparison of biplanar video
radiography and optical motion capture for foot and ankle kinematics.
Frontiers in Bioengineering and Biotechnology, 7, 199. https://doi.org/10.
3389/fbioe.2019.00199https://www.frontiersin.org/articles/10.3389/
fbioe.2019.00199/full
Knapik, J., Harman, E., & Reynolds, K. (1996). Load carriage using packs: A review
of physiological, biomechanical and medical aspects. Applied Ergonomics, 27
(3), 207–216. https://doi.org/10.1016/0003-6870(96)00013-0
Kulessa, D. J., Gollhofer, A., & Gehring, D. (2017). The inuence of football
shoe characteristics on athletic performance and injury risk–a review.
Footwear Science, 9(1), 49–63. https://doi.org/10.1080/19424280.2017.
1284273
Luo, G., & Stefanyshyn, D. (2011). Identication of critical traction values for
maximum athletic performance. Footwear Science, 3(3), 127–138. https://
doi.org/10.1080/19424280.2011.639807
Matthew, D., & Delextrat, A. (2009). Heart rate, blood lactate concentration,
and time–motion analysis of female basketball players during competi-
tion. Journal of Sports Sciences, 27(8), 813–821. https://doi.org/10.1080/
02640410902926420
Matthias, E. C., Banwell, H. A., & Arnold, J. B. (2021). Methods for assessing
footwear comfort: A systematic review. Footwear Science, 13(3), 255–274.
https://doi.org/10.1080/19424280.2021.1961879
Mills, K., Blanch, P., & Vicenzino, B. (2010). Identifying clinically meaningful
tools for measuring comfort perception of footwear. Medicine and
Science in Sports and Exercise, 42(10), 1966–1971. https://doi.org/10.
1249/MSS.0b013e3181dbacc8
Morgan, O. J., Drust, B., Ade, J. D., & Robinson, M. A. (2021). Change of
direction frequency o the ball: New perspectives in elite youth soccer.
Science and Medicine in Football, 1–10. just-accepted. https://doi.org/10.
1080/24733938.2021.1986635
Morio, C., Lake, M. J., Gueguen, N., Rao, G., & Baly, L. (2009). The inuence of
footwear on foot motion during walking and running. Journal of
Biomechanics, 42(13), 2081–2088. https://doi.org/10.1016/j.jbiomech.
2009.06.015
Morio, C. Y. M., Sissler, L., & Guéguen, N. (2015). Static vs. dynamic friction
coecients, which one to use in sports footwear research? Footwear
Science, 7(sup1), S63–S64. https://doi.org/10.1080/19424280.2015.1038609
Morio, C., Bourrelly, A., Sissler, L., & Gueguen, N. (2017). Perceiving
slipperiness and grip: A meaningful relationship of the
shoe-ground interface. Gait & Posture, 51, 58–63. https://doi.org/10.
1016/j.gaitpost.2016.09.029
Morio, C. Y., & Herbaut, A. (2018). Neuromechanical adaptations to slippery
sport shoes. Human Movement Science, 59, 212–222. https://doi.org/10.
1016/j.humov.2018.04.016
Myers, C. A., Allen, W., Laz, P. J., Lawler-Schwatz, J., & Conrad, B. P. (2019).
Motorized self-lacing technology reduces foot-shoe motion in basket-
ball shoes during dynamic cutting tasks. Footwear Science, 11(sup1),
S189–S191. https://doi.org/10.1080/19424280.2019.1606326
Robinson, G., O’Donoghue, P., & Wooster, B. (2011). Path changes in the
movement of English premier league soccer players. The Journal of
Sports Medicine and Physical Fitness, 51(2), 220–226. https://europepmc.
org/article/med/21681155No DOI is visible on the paper
Sekulic, D., Pehar, M., Krolo, A., Spasic, M., Uljevic, O., Calleja-González, J., &
Sattler, T. (2017). Evaluation of basketball-specic agility: Applicability of
preplanned and nonplanned agility performances for dierentiating
playing positions and playing levels. The Journal of Strength &
Conditioning Research, 31(8), 2278–2288. https://doi.org/10.1519/JSC.
0000000000001646
Shinohara, J., & Gribble, P. (2013). Eects of ve-toed socks with multiple
rubber bits on the foot sole on static postural control in healthy young
adults. The Journal of Physical Fitness and Sports Medicine, 2(1), 135–141.
https://doi.org/10.7600/jpfsm.2.135
Sigward, S. M., & Powers, C. M. (2006). The inuence of gender on knee
kinematics, kinetics and muscle activation patterns during side-step
cutting. Clinical Biomechanics, 21(1), 41–48. https://doi.org/10.1016/j.clin
biomech.2005.08.001
Staco, A., Steger, J., Stuessi, E. D. G. A. R., & Reinschmidt, C. (1996). Lateral
stability in sideward cutting movements. Medicine and Science in Sports
and Exercise, 28(3), 350–358. https://doi.org/10.1097/00005768-
199603000-00010
Starbuck, C., Damm, L., Clarke, J., Carré, M., Capel-Davis, J., Miller, S., &
Dixon, S. (2016). The inuence of tennis court surfaces on player percep-
tions and biomechanical response. Journal of Sports Sciences, 34(17),
1627–1636. https://doi.org/10.1080/02640414.2015.1127988
Sterzing, T., Müller, C., Hennig, E. M., & Milani, T. L. (2009). Actual and
perceived running performance in soccer shoes: A series of eight
studies. Footwear Science, 1(1), 5–17. https://doi.org/10.1080/
19424280902915350
Sterzing, T., Lam, W. K., & Cheung, J. T. M. (2012). Athletic footwear research
by industry and academia. In R. S. Goonetilleke (Ed.), The science of
footwear (pp. 605–622). CRC Press, Taylor & Francis Group.
Van Tiggelen, D., Wickes, S., Coorevits, P., Dumalin, M., & Witvrouw, E.
(2009). Sock systems to prevent foot blisters and the impact on overuse
injuries of the knee joint. Military Medicine, 174(2), 183–189. https://doi.
org/10.7205/MILMED-D-01-8508
Wunderlich, R. E., & Cavanagh, P. R. (2001). Gender dierences in adult foot
shape: Implications for shoe design. Medicine and Science in Sports and
Exercise, 33(4), 605–611. https://doi.org/10.1097/00005768-200104000-
00015
JOURNAL OF SPORTS SCIENCES 9