Isokinetic imbalance of adductor–abductor hip muscles in professional soccer players with chronic adductor-related groin pain

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Isokinetic imbalance of adductor–abductor hip muscles in professional soccer players with chronic adductor-related groin pain

K. Belhaj, S. Meftah, L. Mahir, F. Lmidmani & A. Elfatimi

To cite this article: K. Belhaj, S. Meftah, L. Mahir, F. Lmidmani & A. Elfatimi (2016):

Isokinetic imbalance of adductor–abductor hip muscles in professional soccer players with chronic adductor-related groin pain, European Journal of Sport Science, DOI:

10.1080/17461391.2016.1164248

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ORIGINAL ARTICLE

Isokinetic imbalance of adductor–abductor hip muscles in professional soccer players with chronic adductor-related groin pain

K. BELHAJ, S. MEFTAH, L. MAHIR, F. LMIDMANI, & A. ELFATIMI

Department of Physical Medicine and Rehabilitation, Ibn Rochd University Hospital, Casablanca, Morocco

Abstract

This study aims to compare the isokinetic profile of hip abductor and adductor muscle groups between soccer players suffering from chronic adductor-related groin pain (ARGP), soccer players without ARGP and healthy volunteers from general population. Study included 36 male professional soccer players, who were randomly selected and followed-up over two years. Of the 21 soccer players eligible to participate in the study, 9 players went on to develop chronic ARGP and 12 players did not. Ten healthy male volunteers were randomly selected from the general population as a control group.

Comparison between the abductor and adductor muscle peak torques for players with and without chronic ARGP found a statistically significant difference on the dominant and non-dominant sides (p< .005), with the abductor muscle significantly stronger than the adductor muscle. In the group of healthy volunteers, the adductor muscle groups were significantly stronger than the abductor muscle groups on both dominant and non-dominant sides (p< .05). For the group of players who had developed chronic ARGP, abductor–adductor torque ratios were significantly higher on the affected side (p= .008). The adductor muscle strength was also significantly decreased on the affected side. This imbalance appears to be a risk factor for adductor-related groin injury. Therefore, restoring the correct relationship between these two agonist and antagonist hip muscles may be an important preventative measure that should be a primary concern of training and rehabilitation programmes.

Keywords:Football, hip, groin, muscle strength, torque

Introduction

Groin pain is a frequent problem in sport, especially in sports requiring change of direction such as soccer and ice hockey, and frequently leads to absence from sporting activities (Werner, Hagglund, Waldén, & Ekstrand, 2009). Approximately 5–18%

of all sports injuries are groin related (Ryan, DeBurca, & Mc Creesh, 2014). Adductor strains are the most common groin injury among athletes, accounting for approximately 10% of all injuries in football players (Werner et al.,2009). Furthermore, reduced hip adduction strength appears to be related to an increased risk of sustaining a future groin injury (Arnason et al., 2004; Lorentzon, Wedren, & Pietila, 1988; Nicholas & Tyler, 2002;

Tyler, Nicholas, Campbell, & McHugh, 2001;

Werner et al., 2009). Previous studies found that the imbalance of strength between the adductor and abductor muscles is a risk factor for groin injuries

(Arnason et al., 2004; Davies, 1984; Hölmich, 2007; Quittan et al., 2001; Tyler et al., 2001). Hip adductor strength less than 80% of abductor strength in ice hockey players was a risk factor for groin injury (Tyler et al., 2001). According to this study, the development of chronic adductor-related groin pain (ARGP) in the athlete hip joints with significantly low adductor muscle strength suggests that the weakness of this muscle is a risk factor for chronic ARGP.

There are different methods of muscle strength testing: manual muscle testing, hand-held dynamometry and isokinetic dynamometry. Isokinetic dynamometry has been found to be a reliable device for strength muscle measurements in the lower limb, but the majority of the studies have focused on the knee (Davies, Wilk, & Ellenbecker, 1997; Li, Wu, Maffulli, Chan, & Chan, 1996; Quittan et al., 2001). Relatively few studies have documented measurement of hip muscle strength in professional athletes, especially for hip abductor and adductor

Correspondence: Karima Belhaj, Department of Physical Medicine and Rehabilitation, Ibn Rochd University Hospital, Casablanca, Morocco. E-mail: belhajkarima2@gmail.com

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muscle strength (Davies, 1984; Murray & Sepic, 1968; O’Connor,2004).

The aim of this study was to report isokinetic profile of hip abductor and adductor muscle groups in soccer players who go onto suffer chronic ARGP and compare the isokinetic torques of hip abductors/adductors in soccer players suffering from chronic ARGP, with soccer players without ARGP and healthy volunteers from general population.

Methods

Study design and participants

The prospective cohort study included 36 male professional soccer players who were randomly selected from 16 clubs involved in the Moroccan professional league (Botola Pro). Sixty-two potential participants were referred from clubs after specific invitation. After three months of recruitment with interview and examination, 36 players fulfilled the inclusion criteria. To be included in the study, players had to be male, aged 18–30 years, with normal clinical examination especially in the groin region, and to have trained 5–6 times a week and played 1–2 games weekly. In addition, participants had to have a desire to continue sports and partici- pation in the study. The exclusion criteria selections were: history of groin pain or low back pain; previous hip surgery; clinical evidence of ARGP; clinical findings indicating inguinal or femoral hernia;

and other lesions of the lower extremities in the previous six months before the study. The study is focalised on chronic ARGP related to soccer and not on other aetiology of groin pain, therefore, players were excluded from the final analysis (after two years) if they had any other hip injury or injury that suspended soccer practice for more than one year.

Clinical evaluation and isokinetic muscle strength testing on the hip adductor and hip abductor muscles were conducted by a single experienced sports medicine physician during the mid-season competition break in the Department of Physical Medicine and Rehabilitation of Ibn Rochd University of Morroco. A group of 10 healthy male volunteers were randomly selected from the general population as a control group. These participants were tested at the same time as the soccer players for isokinetic strength of the abductor and adductor groups using the same protocol. Analyses were made between the three groups.

All participants provided written informed consent and the research protocol was approved by the Ethics in Research with Human Beings Committee of our institution (Ibn Rochd university Hospital).

Isokinetic testing

(1) Equipment. The tests were carried out using a CYBEX Norm Isokinetic Dynamometer System (CSMI) to measure isokinetic joint torques of hip abduction and adduction in the concentric mode. It was driven by Human Assessment Computer (HUMAC) for Windows. The dynamometer was recalibrated according to the specifications outlined by the manufacturer’s instructions.

(2) Positioning of the subjects. The dominant and non-dominant sides were determined by asking the player “which leg to you kick a ball with?” and then both legs were tested. Subjects were posi- tioned correctly by a sports medicine physician on the CYBEX Dynamometer in a side-lying position for hip abduction–adduction measurements. Two wide belts were secured at the levels of the anterior superior iliac spine and the knee to stabilise the body and minimise muscle compensation. The axis of the dynamometer was aligned with the abduction–adduction axis of the hip. The support lever was fixed at the lower end of the thigh. All measurements incorporated a gravity- correction procedure. During the test, testers gave verbal feedback as needed to maintain proper positioning.

(3) Testing protocol. All soccer players were instructed not to undertake exercise, training or match on the day before the evaluation. Only conven- tional concentric isokinetic tests were used. The angle of abduction and adduction was 45° and 30°, respectively. These speeds are recommended by Cybex, and correlate well with joint velocities during functional tasks. The participants performed a 10-minute warm up on a bike, then to become fam- iliar with the testing protocol, performed three repetitions of each test at 60°/s and 120°/s, one which was a maximal contraction (Snow & Blacklin, 1992). The protocol consisted of five repetitions at the speed of 60°/s followed by 10 repetitions at 120°/s. One-minute recovery was the period allowed between both series. A 3-minute rest was allowed between each side. The dominant side was tested first and the order of speed was from the slowest to fastest, as suggested by Wilhite, Cohen, and Wilhite (1992). All evaluation tests were conducted by the same sports medicine physician follow- ing the same procedure. All participants were motivated through verbal encouragement to exert maximal efforts (Perrin, 1993). The strength parameters (peak torques) were evaluated at the speed of 60°/s (medium) and the muscular power parameters at 120°/s (high). In this study, only strength parameters were analysed because this was the focus of this study.

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Data collection

Peak torque (N/m) was calculated by measuring the highest concentric torque for the abduction and adduction movements noted at 60°/s angular speeds. Only values that had good reproducibility were analysed. Good reproducibility of the measure required an identical torque curve for three complete and successive abduction–adduction movements for each test (Mawdsley & Knapik, 1982; Ostemig, 1986). The reproducibility was assessed by the machine during the repetitions. The reliability of protocol evaluations used in our department was assessed previously for all articulations, and the hip isokinetic abduction–adduction test was reliable, with a test–retest intraclass correlation coefficient of 0.79. Clinical diagnostic criteria for ARGP were:

tenderness localised to the adductor muscles inser- tion, pain on passive stretch of the adductors and/

or pain on adduction against resistance (Weir et al., 2015). All clinical symptoms were present for at least two months. The players were followed for two years and monitored for groin pain/groin injury. At the end of the two years, the soccer players were categorised into injured and non- injured groups.

Statistical analysis

The data were analysed using IBM SPSS (Version 20.0). The normal distribution was assessed by using Shapiro–Wilk test and skewness by Kurtosis z-values. The demographic characteristics were summarised by means and standard deviations (SD). Paired t-tests were performed to determine the mean difference between dominant versus non-dominant limbs and agonist (abductor) versus antagonist (adductor) muscle groups for all outcome measures. The Wilcoxon signed-rank test was used to compare abductor–adductor torque ratios between affected and non-affected sides for the group of players who had developed chronic ARGP. The significance level was set at a value of p< .05.

For soccer players, the Kruskal–Wallis (KW) ANOVA test was used to compare abductor– adductor peak torque ratios between three groups of participant limb according to chronic ARGP; the first composed of hips which developed chronic ARGP (mean ratios = 3.11 ± 2.52), the second included asymptomatic hip joints among players who had developed chronic ARGP (mean ratios = 1.53 ± 0.49) and the third group was asymptomatic hip joints of players who had not developed chronic ARGP (mean ratios = 1.20 ± 0.27). Mann–Whitney Utests were used to further analyse findings. A Bon- ferroni correction was applied and all effects are reported at the 0.017 (0.05/3) level of significance.

For healthy volunteers, the same analysis was done between the dominant and non-dominant sides.

Results

For the soccer group, 36 players were recruited and 15 were excluded over the two-year period, leaving 21 players included in the final analysis: 9 subjects developed chronic ARGP and 12 asymptomatic soccer players. Ten healthy male volunteers were recruited. All participant characteristics are presented inTable I. There was no significant difference in age, height and mass between the three groups (p> .05).

For all soccer players and healthy volunteers there were no significant differences in peak torque (N/m) between the dominant and non-dominant abductor muscle groups, or between the dominant and non- dominant adductor muscle groups. Furthermore, there was no significant difference between the abductor–adductor torque ratios on the dominant and non-dominant sides for the hip in the isokinetic concentric exercise mode (Table II).

For the soccer players, comparison between the abductor–adductor peak torques for the ARGP group and the non-ARGP group found a statistically significant difference in strength on both the dominant and non-dominant sides (p was .0001 and .002 for dominant and non-dominant side, respectively), and the abductor muscle was significantly stronger than the adductor muscle (Table II).

Table I. Subject characteristics (ARGP, asymptomatic players and healthy volunteers).

Characteristics Players with chronic ARGP (n= 9) Asymptomatic players (n= 12) Volunteers (n= 10)

Mass (kg) 78.56 ± 8.07 73.58 ± 5.30 75.42 ± 6.10

Height (m) 1.84 ± 0.08 1.80 ± 0.06 1.81 ± 0.05

Age (y) 24.11 ± 3.02 23.17 ± 3.88 23.51 ± 3.15

Right dominant side (number) 8 10 9

Left dominant side (number) 1 2 1

Values are represented with mean ± standard deviation (SD).

ARGP: adductor-related groin pain.

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In the group of healthy volunteers, the abductor– adductor peak torques were statistically different on both sides (p< .05), and in contrast to the soccer group the adductor muscles group was significantly stronger than the abductor muscles group (Table II).

For the soccer players who had developed chronic ARGP, abductor–adductor torque ratios were significantly higher on the affected side than on the non-affected side. The adductor muscle strength was significantly decreased on the affected side (Table III).

Abductor–adductor hip peak torque ratios were significantly high in player hip joints that had developed chronic ARGP (H(2) = 18.98).

Discussion

This study elucidates the relationship between abductor–adductor muscle group imbalance in professional soccer players and predisposition for chronic ARGP. Values are presented for the dominant and non-dominant sides and not for the right and left sides for two reasons. First, the objective of this study was to analyse the relationship between isokinetic hip adduction and hip abduction strength in

the dominant and the non-dominant sides. And second was to analyse the muscle strength imbalance between sides, due to a specific training or sport (soccer). For this reason comparison with a control group of regular healthy people was conducted.

Values of the group of players suffering from chronic ARGP were presented for the affected and unaffected sides.

Leg dominance in soccer players and healthy volunteers had no impact on the abductor–adductor hip muscle peak torques or the ratios, which supports findings from previous studies (Kellis & Katis,2007;

Masuda, Kikuhara, Takahashi, & Yamanaka, 2003;

Mohammad, Abdelraouf, Elhafez, Abdel-Aziem, &

Nassif,2014).

The soccer players had significant higher hip abductor strength than hip adductor. Sugimoto, Mattacola, Mullineaux, Palmer, and Hewett (2014) found that collegiate athletes had non-significant greater hip abductor strength. This result reported by Sugimoto et al. (2014) was non-significant and also did not concern specific professional sport population. In contrast, previous studies in general and athletic popu- lations have reported higher isokinetic peak torque values in hip adductors rather than hip abductors (Baldon et al., 2009; Burnett, Betts, & King, 1990;

Table II. Hip abduction and adduction concentric isokinetic profile in the speed of 60°/s for the dominant and non-dominant sides.

Isokinetic strength

Players with ARGP (n= 9) Asymptomatic players (n= 12) Volunteers (n= 10)

Dom Non-Dom Dom Non-Dom Dom Non-Dom

Abd-peak torque (N/m) 145.00 ± 29.55 145.00 ± 26.39 129.17 ± 22.87 131.83 ± 19.14 79.50 ± 23.37 79.30 ± 20.85 Add-peak torque (N/m) 71.78 ± 37.10 99.33 ± 36.69 111.25 ± 23.97 115.50 ± 36.77 101.50 ± 16.89 102.90 ± 15.74 Abd/Add-peak torque ratios 3.04 ± 2.57 1.60 ± 0.51 1.18 ± 0.21 1.22 ± 0.33 0.78 ± 0.21 0.76 ± 0.16 Values are represented with mean ± standard deviation (SD).

N/m: Newton/metre.

Dom: Dominant side.

Non-Dom: Non-Dominant side.

Abd: Abductor muscle.

Add: Adductor muscle.

Table III. Hip abduction and adduction concentric isokinetic profile in the speed of 60°/s for the affected and non-affected side (for players with ARGP).

Isokinetic strength

Players with ARGP (n= 9)

Affected side Non-affected side Sig (p)

Abductor muscle peak torque (N/m) 147.22 ± 29.55 142.78 ± 26.19 .63

Adductor muscle peak torque (N/m) 69.56 ± 36.32 101.56 ± 35.42 .09

Abductor–adductor peak torque ratios 3.11 ± 2.52 1.53 ± 0.49 .008^∗

Values are represented with mean ± standard deviation (SD).

ARGP: adductor-related groin pain.

Sig: significance (p< .05).

N/m: Newton/metre.

∗Significant (p< .05) difference between the affected and non-affected hips.

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Cahalan, Johnson, & Chao, 1989; Donatelli, Catlin, Backer, Drane, & Slater, 1991; Ihara, Cevales, &

Pinto, 2000; Johnson, Mille, Martinez, Crombie, &

Rogers,2004; Kea, Kramer, Forwell, & Birmingham, 2001; Niemuth, Johnson, Myers, & Thieman, 2005;

Poulmedis,1985; Tippet,1986).

All studies reported in the literature of similar age and population and using a similar test procedure have shown an abductor–adductor ratio under one;

Donatelli et al. (1991) found a normal ratio between 0.41 and 0.48 and Poulmedis (1985) equal to 0.74. Therefore, the present study suggests that professional soccer players had an imbalance of strength in abductor–adductor muscle groups in comparison with general population and other athletes reported by previous studies. These findings suggest the game of soccer predisposes players to an abductor–adductor muscle group imbalance.

In addition, players who had developed chronic ARGP presented a significant abductor–adductor imbalance in the specific involved leg. This imbalance, which was confirmed by comparison with asymptomatic players and control group of regular healthy people, can be considered a risk factor for professional soccer players to developing further chronic ARGP.

Adductor strains are the primary focus of groin injury prevention programmes (Ibrahim, Murrell, &

Knapman,2007). Many football injuries could prob- ably be avoided if training programme and methods were scientifically modified. Soccer seems to be a strengthening activity for the hip abductors and this evolution requires strength adaptations in the other antagonist muscles (adductors) (Thorborg, Couppe, Petersen, Magnusson, & Hölmich,2011).

This study was designed to evaluate hip muscle strengths in Moroccan soccer players and to provide further information that can be used in training and rehabilitation programme with the aim of potentially reducing risk of muscle strains.

There are number of strengths of this study that should be taken into account. The muscle evaluation used isokinetic testing, which has higher validity and reliability than hand-held dynamometry. There were strict inclusion and exclusion criteria with a prospective study design and a control group. However, limitation of this study was the small sample size, which may reduce statistical power, but the fact that the enrolled participants were professional soccer players may explain this sample size.

Conclusions

This study found an imbalance of strength in abductor–adductor muscle groups in professional soccer

players. The players who developed chronic adductor-related groin injuries had stronger abductor muscles and weaker adductor muscles, and therefore suffered abductor–adductor imbalances compared to general population and previous studies. This imbalance seemed to be a risk factor for adductor-related groin injury. Therefore, restoring the correct relationship between agonist and antagonist hip muscle groups could be an important preventative measure that should be of primary interest of the training and rehabilitation programmes. In the future, it will be interesting to examine the development of ARGP in soccer players after hip strength imbalance correction.

Disclosure statement

No potential conflict of interest was reported by the authors.

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