Plantar pressure asymmetry and risk of stress injuries in the foot of young soccer players

Accepted Manuscript Plantar pressure asymmetry and risk of stress injuries in the foot of young soccer players Renato Azevedo, Emmanuel S. da Rocha, Pedro S. Franco, Felipe P. Carpes PII:

S1466-853X(16)30129-8

DOI:

10.1016/j.ptsp.2016.10.001

Reference:

YPTSP 778

To appear in:

Physical Therapy in Sport

Received Date: 1 February 2016 Revised Date:

8 October 2016

Accepted Date: 16 October 2016

Please cite this article as: Azevedo, R., da Rocha, E.S., Franco, P.S., Carpes, F.P., Plantar pressure asymmetry and risk of stress injuries in the foot of young soccer players, Physical Therapy in Sports (2016), doi: 10.1016/j.ptsp.2016.10.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT PLANTAR PRESSURE ASYMMETRY AND RISK OF STRESS INJURIES IN THE FOOT OF YOUNG SOCCER PLAYERS

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Renato Azevedo1,2, Emmanuel S da Rocha1,2, Pedro S Franco1,2, Felipe P Carpes1,2,*

Applied Neuromechanics Research Group, Faculty of Health Sciences, Federal University of Pampa, Uruguaiana, RS, Brazil.

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Graduate Program in Physical Education, Physical Education and Sports Centre,

* corresponding author: Felipe P Carpes, Ph.D

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Federal University of Santa Maria, Santa Maria, RS, Brazil.

Postal address: Federal University of Pampa - Laboratory of Neuromechanics

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BR 472 km 592 - ZIP 97500-970, Uruguaiana, RS, Brazil Phone: +55 55 3911 0200 ext 9977

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e-mail: [email protected]

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Acknowledgements

Authors would like to thank CAPES-Brazil for the student fellowships provided to RRB and PSF, and FAPERGS-Brazil for student fellowship provided to ESR during the development of this research. This research was partially financed by research grants from FAPERGS-Brazil awarded to FPC.

Conflict of interest statement None.

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PLANTAR PRESSURE ASYMMETRY AND RISK OF STRESS INJURIES IN THE FOOT OF YOUNG SOCCER PLAYERS

Abstract Background: Asymmetries in the magnitude of plantar pressure are considered a risk

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factor for stress fracture of the fifth metatarsal in soccer athletes.

Objective: To investigate the presence of plantar pressure asymmetries among young soccer athletes.

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Design: Observational. Setting: Laboratory.

matched control group (n=15).

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Participants: Thirty young adolescents divided into a soccer player group (n=15) or a

Main outcome measures: Mean plantar pressure was determined for seven different regions of the foot. Data were compared between the preferred and non-preferred foot, and between the groups, during barefoot standing on a pressure mat system.

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Results: Higher pressure was found in the hallux, 5th metatarsal and medial rearfoot of the non-preferred foot in the young soccer players. These asymmetries were not

the groups.

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observed in the control group. Magnitudes of plantar pressure did not differ between

Conclusion: Young soccer players present asymmetries in plantar pressure in the

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hallux, 5th metatarsal and medial rearfoot, with higher pressure observed in the nonpreferred foot.

Keywords: foot; plantar pressure; soccer; fifth metatarsal.

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1. Introduction

Soccer is one of the most popular sports in the world (FIFA, 2007). Soccer athletes are subject to injuries, mostly in the lower extremity (Fachina et al., 2013; Theron, Schwellnus, Derman, & Dvorak, 2013), in part due to the high intensity, continuous changes in movement direction, jump-landing tasks, and sprints requested in training

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and competition (Barnes, Archer, Hogg, Bush, & Bradley, 2014; Di Salvo et al., 2007). The cumulative stress resulting from long-term repetitive movements is considered a common source of overuse injuries such as the fracture in the fifth metatarsal (Bentley,

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Ramanathan, Arnold, Wang, & Abboud, 2011; Porter, Duncan, & Meyer, 2005). This injury has been associated with higher plantar pressure in the lateral region of the foot

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(Ekstrand & van Dijk, 2013; Fetzer & Wright, 2006; Sims, Hardaker, & Queen, 2008), especially among male athletes (Sims et al., 2008). Fracture in the fifth metatarsal was observed in 16 athletes among the 273 athletes (~6%) followed during two years (Fujitaka et al., 2015). Despite of its low incidence, this injury is considered to be serious due to the time it takes to completely recover and the high recurrence rate

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(Ekstrand & van Dijk, 2013).

Asymmetries may play a role in occurrence of injuries among soccer players

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since differences in plantar pressure between the preferred and non-preferred foot were previously reported (Wong et al., 2007), and stress injuries in the foot of soccer

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players have an unilateral pattern, in which the non-preferred foot is the most commonly injured (Fujitaka et al., 2015). It could be related to the functional lateralization of the lower limbs observed for mobilization tasks performed in soccer (i.e. kicking the ball) (Fujitaka et al., 2015). During these mobilization tasks, the contralateral non-preferred leg supports the body weight and provides body stability to the athlete (Ball, 2013; Teixeira, de Oliveira, Romano, & Correa, 2011; Wong et al., 2007). Although the static assessment of plantar pressure may not correlated with the dynamic measure of plantar pressure during the actual practice of soccer, adaptations 2

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related to weight discharge and body balance in soccer athletes can be described from data recorded during static trials (Petry et al., 2016). While a relationship between foot loading, soccer practice and stress injuries in the foot may exist (Carl, Pauser, Swoboda, Jendrissek, & Brem, 2014; Wong et al.,

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2007), most studies only considered these risk factors among adult and/or elite athletes (Bentley et al., 2011; Ekstrand & van Dijk, 2013; Theron et al., 2013). Little attention was given to the young soccer player (Fujitaka et al., 2015). However, soccer is a very popular sport among adolescents (Stolen, Chamari, Castagna, & Wisloff, 2005), and

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stress injuries may limit their participation in training sessions, and, in more extreme cases, affect their professional career in soccer. Analysis of plantar pressure patterns

promoting early prevention.

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in young athletes can help coaches and therapists to minimize risk factors for injury by

Therefore, the goal of this study was to determine whether patterns of plantar pressure associated with foot injuries, e.g., plantar pressure asymmetry, are observed

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among non-injured young soccer players during upright standing. We hypothesized that plantar pressure during standing would be asymmetric among soccer players but not in non-players, and higher plantar pressure would be observed in foot sites

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described by the literature as at higher risk of suffering stress injuries.

2. Methods

2.1. Study design and participants Thirty participants volunteered in this study (see Table 1 for participants details). They were divided in two groups: a group of non-injured young soccer athletes (n=15) and a control group (n=15). Soccer athletes were engaged in regular training at least three times per week each session lasting 90 min in which they were always wearing regular studded soccer boots and participating in State level competitions at least during the 3

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last year. Foot strike pattern was observed and all participants included presented a rearfoot strike pattern during running. Control group included participants with similar age, anthropometric and foot strike characteristics of those observed among the soccer players, but without any training experience other than the regular classes of physical education in the school (i.e. one session of 60 min per week). All participants were free

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of past lower extremity injuries. Participants presenting altered foot arch (i.e. excessive fallen arch as depicted by plantar pressure distribution) were not considered for participation in this study due to the influence of the fallen arches on plantar pressure

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distribution (Barnes et al., 2014). All participants and their parents or legal guardians signed an informed consent form in agreement with the declaration of Helsinki and

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approved by the local ethics committee. Mean plantar pressure was determined during upright standing and analyzed considering different foot regions in the preferred and non-preferred foot.

Table 1. Characteristics of the participants included in this study. Data are reported as

Variables Age (years)

Height (cm)

Soccer (n=15)

Control (n=15)

p-value

14 ± 0.7

14 ± 0.5

0.382

62 ± 9

66 ± 16

0.379

171.7 ± 0.5

173.6 ± 0.8

0.449

3±1

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-

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Body mass (kg)

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mean ± standard deviation.

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Training (years)

p-value: groups were compared using paired t-test and alpha of 0.05.

2.2. Plantar pressure

Plantar pressure was sampled at 100 Hz during barefoot upright standing using a pressure mat system with spatial resolution of 1.4 sensors per cm2 (Matscan, Tekscan Inc., Boston, USA). Three trials were performed where the participants were standing quietly with eyes open during 30 seconds (da Rocha, Bratz, Gubert, de David, & 4

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Carpes, 2014). A 30 seconds interval was conducted between trials. Participant should avoid unnecessary movements, keep their arms relaxed along the body and look at a reference point positioned 3 meters in front and at the level of their eyes. The mean plantar pressure was determined considering regions of the hallux, head of first metatarsal (M1), head of fifth metatarsal (M5), midfoot (MF), medial rearfoot (MR) and

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lateral rearfoot (LR), as described elsewhere (Carl et al., 2014). Plantar pressure was normalized to the average foot pressure considering the entire foot, therefore minimizing effects of small variations in body mass between the participants

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(Fernandez-Seguin et al., 2014).

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2.3 Foot sensitivity

To avoid the influence of altered foot sensitivity on plantar pressure distribution, foot sensitivity was determined in both groups. We used a Semmes–Weinstein pressure aesthesiometer (Semmes-Weinstein Monofilaments, San Jose, CA, USA), with varying diameter producing a standardized pressure to the skin (Semmes-Weinstein filaments

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markings 1.65 - 6.65 kgf, according to the calibration of the manufacturer) and applying according to the manufacturer recommendation of use (Holewski, Stess, Graf, & Grunfeld, 1988). The filaments were pressed at specific points onto the plantar surface

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of the preferred and non-preferred foot: hallux, head of first metatarsal (M1), head of fifth metatarsal (M5), midfoot (MF), medial rearfoot (MR) and lateral rearfoot (LR) (see

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the numbers in the Figure 1). Procedures were the same as described in a previous report and therefore are not further detailed here (da Rocha et al., 2014).

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Figure 1. Foot regions where mean plantar pressure was determined (boxes), and sites where foot sensitivity was assessed (black dots). 1: hallux; 2: head of first metatarsal; 3: head of fifth metatarsal; 4: lateral midfoot; 5: medial rearfoot; 6: lateral

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2.4. Statistical analyses

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rearfoot.

Data distribution was tested using Shapiro-Wilk test. Age, body mass, and height were compared between soccer and control groups by independent t tests. Foot sensitivity was compared between the preferred and non-preferred foot by paired t test, and

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between soccer and control groups by independent t test. Plantar pressure was averaged for each foot region and an analysis of variance for repeated measured in a 2 x 2 model was used to identify group (soccer vs control), or foot preference effects

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(preferred vs non-preferred) as well as significant interactions. When a main effect or interaction was observed, preferred and non-preferred feet were compared with paired

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t test. Sample size calculations were based on plantar pressure data from a previous study (da Rocha et al., 2014). Sample size was estimated in 13 subjects to ensure a statistical power of 80% for effect size of 0.2 (G-Power 3.1.9 software). Fifteen volunteers per group were recruited with consideration of dropouts. Asymmetry index was determined for each foot region considering the equation AI% = [(preferred – nonpreferred)/preferred*100] to illustrate the differences in the mean plantar pressure between the feet. The asymmetry index for each foot region was compared between

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groups using independent t test. All analyses considered a significance level of 0.05 using a commercial statistical package.

3. Results

and non-preferred feet (Table 2).

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Foot sensitivity did not differ between the groups and did not differ between preferred

Table 2. Foot sensitivity. Sensitivity data are presented in log10 values. Preferred

Non Preferred

Hallux

0.48 ± 0.17

Head of 1st metatarsal

0.50 ± 0.19

Head of 5th metatarsal

0.52 ± 0.18

0.56 ± 0.15

0.068

Lateral midfoot

0.54 ± 0.17

0.55 ± 0.15

0.276

Medial rearfoot

0.58 ± 0.14

0.59 ± 0.15

0.588

Lateral rearfoot

0.60 ± 0.14

0.60 ± 0.14

0.317

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Foot region

p-value

0.450

0.52 ± 0.16

0.558

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0.50 ± 0.17

The magnitudes of mean plantar pressure were similar between the groups, but

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interactions between the factors group and foot preference were found in the hallux (F=9.84; P=0.007), MR (F=5.60; P=0.03) and M5 (F=9.31; P=0.009). Therefore, for

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these regions, plantar pressure was compared between the preferred and nonpreferred feet in each group. Asymmetric plantar pressure was found among the young soccer players, with higher pressure in the hallux (t=-2.670; P<0.01) and M5 (t=-4.247; P<0.01) in the non-preferred foot, and higher pressure in the MF in the preferred foot (t=3.118; P<0.01). Asymmetries were not observed among controls. Asymmetry indexes were higher in the soccer players than in the controls (Table 3). Our results showed asymmetric plantar pressure in the fifth metatarsal, with higher pressure in the non-preferred foot in the soccer players' group. 7

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Table 3. Asymmetry indexes determined for each foot region in soccer and control groups. Data are presented as mean and standard deviation. Negative values indicate higher pressure in the non-preferred foot. Soccer (n=15)

Hallux

-53 ± 87* 19 ± 31

Head of 5th metatarsal

-70 ± 87*

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Head of 1st metatarsal

Control (n=15)

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Foot regions

10 ± 25 3 ± 17

-10 ± 19

- 4 ± 49

1 ± 13

Medial rearfoot

-17 ± 24*

-13 ± 16

Lateral rearfoot

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Lateral midfoot

18 ± 22

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* different of the control (P<0.05).

4±8

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Figure 2. Plantar pressure, expressed as percentage of total pressure (vertical bars) and standard deviation (vertical lines), in the soccer and control groups. * indicates difference between the preferred and non-preferred foot. M1: first metatarsal; M5: fifth

4. Discussion

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metatarsal; MF: midfoot; LR: lateral rearfoot; MR: medial rearfoot.

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Here we investigated whether patterns of asymmetry in the mean plantar pressure, suggested as a risk factor of foot injuries in adult soccer players, are observed among

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young soccer players. Performing a static assessment of plantar pressure, we found asymmetric plantar pressure in regions reported by the literature as having higher risk of stress injury among adult soccer players (Ekstrand & van Dijk, 2013; Fetzer & Wright, 2006). Magnitudes of plantar pressure and foot sensitivity did not differ between the groups. The consideration of static measurement of plantar pressure is a limitation, despite of the fact that we found results similar to those from a previous study including dynamic measurements in adult players (Wong et al., 2007). The 9

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asymmetries observed in our study for young athletes need further investigation considering the long-term effects of continuous practice of soccer. Our results showed asymmetric plantar pressure in the fifth metatarsal, with higher pressure in the non-preferred foot. The fifth metatarsal is one of the foot regions susceptible to stress injuries among soccer athletes (Ekstrand & van Dijk, 2013; Hunt

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et al., 2014; Porter et al., 2005). Stress facture of the fifth metatarsal has been associated higher load in the lateral region of the foot (Ekstrand & van Dijk, 2013; Fetzer & Wright, 2006). Furthermore, soccer produces a consistent functional

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lateralization in performance of mobilization tasks (Carey et al., 2001). In this sense, the non-preferred foot supports body weight (Ball, 2013). The greater pressure in the

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region of the fifth metatarsal in the non-preferred foot during static assessment of plantar pressure is similar to recent results from dynamic approaches (Petry et al., 2016), and for specific soccer tasks like change of directions (Wong et al., 2007). Our main results suggest these asymmetric characteristics are also present among young

limitation of our study.

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athletes. However, we cannot exclude the static measurement of plantar pressure as a

The plantar pressure asymmetry in young soccer players requires attention of coaches and physiotherapists. The asymmetries produced higher pressure in the non-

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preferred leg. The non-preferred leg is often subjected to higher loading due to its role for stabilization tasks (Teixeira et al., 2011). Furthermore, movements requiring change

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of direction in soccer will involve higher traction and breaking forces in the nonpreferred foot (Wong et al., 2007). Considering adult athletes, a higher incidence of fifth metatarsal fracture in the non-preferred foot was previously documented (Ekstrand & van Dijk, 2013; Fujitaka et al., 2015). Despite of the similar magnitude of static plantar pressure between soccer players and non-players, the most relevant result is that asymmetries in plantar pressure were present only in the group of soccer players. The asymmetry observed in the hallux is an important result in the context of injury risk. Previous reports described 10

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hallux as a region receiving higher pressure among soccer players (Bentley et al., 2011; Carl et al., 2014; Sims et al., 2008). This previous observation was also reported in our data concerning static assessment of plantar pressure distribution. Following the asymmetric load in the medial rearfoot, the higher loading in the medial area of the foot and hallux may also contribute to higher chance of ankle inversion (Rice et al., 2013).

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Different from previous studies that examined plantar pressure patterns in soccer players (Bentley et al., 2011; Sims et al., 2008), we performed a static assessment of plantar pressure distribution. Whether this is a limitation or not needs

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further exploration as our results for the young athletes are in agreement with dynamic measurements accomplished in adult athletes. Static assessment also showed

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asymmetries similar to the observed during dynamics assessment of the soccer players (Wong et al., 2007). Furthermore, static assessment can be a quicker, cheaper and easier protocol of testing to be added to testing routines, different from the dynamic assessment that requires more hardware and time. Our study has limitations. It would be valuable to verify postural alignments in the lower limbs and the traction

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force in the toe flexion, which are variables related to injury risk in the foot (Fujitaka et al., 2015). In addition, a follow up study would permit to determine if asymmetries

5. Conclusion

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observed in the childhood could in fact result in injury in the adulthood.

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Young soccer players present asymmetries in plantar pressure in the hallux, 5th metatarsal and medial rearfoot, with higher pressure observed in the non-preferred foot. The asymmetries observed in the young soccer players suggest that they have specific adaptation that may result from mechanical demands during soccer practice. .

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Conflict of Interest None declared.

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ACCEPTED MANUSCRIPT PLANTAR PRESSURE ASYMMETRY AND RISK OF STRESS INJURIES IN THE FOOT OF YOUNG SOCCER PLAYERS

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Highlights:

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Young soccer players present asymmetric plantar pressure.

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Greater plantar pressure is observed in non-preferred foot of young soccer players.

Young soccer players might be at higher risk of stress injury in the foot.

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Ethical approval for the study was received from the Federal University of Pampa

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Human Research Ethics Committee.

ACCEPTED MANUSCRIPT Funding This research was partially financed by research grants from FAPERGS-Brazil

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awarded to FPC.