Abstract
Background
Static postural control disorders have been documented in soccer players suffering from groin pain (GP). Understanding the mechanisms of these disorders is crucial in designing rehabilitation programs.
Objectives
To (i) assess static postural control and core stability in soccer players suffering from GP compared to their peers and (ii) explore the relationship between these two parameters.
Methods
This cross-sectional study involved 42 male soccer players suffering from GP (GP group: GPG) and 42 healthy players (control group: CG). Static postural control (stabilometric platform) and core stability (core endurance tests) were assessed.
Results
Center of pressure velocity in the GPG was significantly higher compared to the CG during bipedal stance on the firm surface with eyes closed (2.66 [95 % CI: 0.86–3.67]; p < 0.01) and on the foam one (p < 0.001) in both conditions; eyes opened (2.88 [95 % CI: 1.42–4.43]) and closed (5.88 [95 % CI: 2.66–9.10]), and on the IL in eyes closed (12.54 [95 % CI: 4.27–20.80]; p < 0.01). Besides, GPG revealed significant (p < 0.001) lower core stability measures compared to CG. No significant associations (p > 0.05) were observed between static postural control and core stability in GPG.
Conclusion
Soccer players suffering from GP showed static disorders of postural control compared with their peers. These impairments were not associated with measures of core stability. These findings provide insight into the direction of future research exploring the mechanisms underlying deficits in static postural control in soccer players suffering from GP.
Keywords: Static balance, Non-time loss groin injury, Core endurance
Highlights
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Players with groin pain had static postural balance disorders compared to controls.
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Core stability was not associated with static balance performance in these players.
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This provides insights for future studies into static balance disorders mechanisms.
1. Introduction
Worldwide, the most popular sport is soccer1 and carries a high risk of injury.2 Regarding this, soccer players sustain frequently groin pain (GP)3 and symptoms are often chronic.4 Due to the persistent aspect of the symptoms, definitions of GP2 may undervalue the injury's true cost and consequences.4 Indeed, per season, non-time-loss GP affect over 59 % of soccer players.5 It has been observed by recent researchers that soccer players suffering from non-time-loss GP perform less than their healthy counterparts in terms of postural control in both static and dynamic conditions.6,7
The capacity to keep the body in its base of support or in static equilibrium is known as static postural control. Dynamic postural control is considered more challenging because it necessitates the capacity to keep balance when moving from a dynamic to a static state.8 It has been demonstrated that having proper postural control is crucial when practicing soccer.9 For this practice, it is a fundamental element in achieving optimum performance and reducing the risk of injury.10 Some authors 11,10 have pointed out that postural control in soccer players needs to be assessed using both static and dynamic tests, because postural control performance is not related to one or the other.
Clinical research has prioritized the improvement of postural control in soccer, given its significance. For soccer players with non-time-loss GP, it is therefore interesting to develop rehabilitation strategies aimed at improving postural control. In these players, postural control disorders may have detrimental effects that could be avoided with such strategies. Understanding the mechanisms underlying the postural performance deficits in these players is essential to achieving this goal. It was shown by our earlier, unpublished data that lower core stability is linked to dynamic postural control impairments in soccer players suffering from non-time-loss GP. Core stability refers to the ability of osteoarticular and muscular structures to maintain or regain a position in the core trajectory while being coordinated by the motor control system.12 Although studies highlight the link between static postural control and trunk stability in different populations,13,14 to our knowledge, no data are available concerning the potential association between these two parameters in soccer players suffering from GP. Consequently, the aims of the present study were to (i) investigate static postural control and core stability in soccer players suffering from GP compared to their healthy peers and (ii) explore the relationship between these two parameters. The hypothesis was that these players would have static postural control disorders compared to controls, and that measures of lower core stability would have a significant detrimental effect on static postural control in soccer players suffering from GP.
2. Methods
2.1. Design and participants
It was a cross-sectional study, agreed by the ethics committee (CPP: 0206/2019) and adhered to Helsinki Declaration. Participants accepted to take part voluntarily, after signing a consent form, and their rights were respected.
By means of the software G*Power, 42 participants were needed for power correlation analysis in this study, considering a large effect size (0.5), an alpha = 0.05 and a power (1-β) = 0.95. Therefore, forty-two male soccer players with groin pain (groin pain group: GPG)3 and 42 healthy players (control group: CG)4 from soccer teams took part in the study. Direct advertising in physiotherapy clinics offering soccer health care was used to recruit cases. An email invitation from their coaches led to the recruitment of controls. Doctors qualified in sports medicine diagnosed15 and forwarded the cases to the research laboratory where the experiments were carried out. Cases were included if they presented with chronic unilateral GP without time-loss. Nevertheless, soccer players with other differential diagnosis of GP were excluded. Besides, participants who present any musculoskeletal pathology or injury in the past year, which could affect postural balance measures, were excluded. Eligible participants at inclusion filled out the questionnaire Copenhagen Hip and Groin Outcome Score (HAGOS) to measure the extent of groin issues at baseline.
2.2. Procedures
2.2.1. Core stability
The following trunk endurance tests were used to assess core stability: trunk extension and flexion tests and side bridge while lying on the DL/NDL for CG, IL/NIL for GPG.16 Measurements were carried out using the previously detailed method.16 For each test position, participants were instructed to adopt isometric postures of maximum duration. The duration of holding the correct position was recorded in seconds. The order of the 4 endurance tests was randomized and given at least 5 min rest between tests to avoid fatigue.
2.2.2. Postural control
A Techno Concept® platform (40 Hz frequency) that records the center of pressure (CoP) excursions was used to assess static postural performance in this study. Soccer players were instructed to stand on this apparatus in both bipedal and unipedal stances, with their arms out to the sides. Participants were in the bipedal stance, barefoot, with their feet standardized. CoP sway was recorded on two surfaces, a foam surface and a firm surface, with the participants' eyes open (EO) and closed (EC). Using a foam surface, the force platform was surmounted by a foam pack. With the unipedal stance, participants stood on one limb (dominant limb (DL)/non-dominant limb (NDL) for CG, injured limb (IL)/non-injured limb (NIL) for GPG) with a 45° flexion of the other limb at the hip and knee, and tests were performed under EO and EC conditions. The average value of three trials was taken into account for the analysis. The mean CoP velocity (CoPVm) was taken into account in this study because it is the most reliable parameter across trials as well as reflecting the effectiveness of the postural control system (the smaller the velocity, the greater the postural control), while at the same time characterizing the net neuromuscular activity involved in maintaining balance.17
2.3. Statistical analysis
The normality as well as the homogeneity of all data were checked using the following tests: Smirnov's Kolmogorov test and Levene's test, respectively. Results are reported as either mean and standard deviation (SD) or as median and 25–75 % interquartile range (HAGOS). Independent t-tests were conducted to compare core stability (flexor and extensor endurance), age, body mass index, body mass and height between groups. In order to analyze between groups HAGOS, weekly training, match exposure and playing experience, independent Mann-Whitney U tests were applied. Because no differences between limbs and sides in static unipedal stance and side bridge results, respectively, were shown by healthy soccer players, DL data were included in the analysis. To analyze the results for side bridges, either independent t-tests were used for GPG versus CG differences, or paired t-tests were used for side comparisons in the GPG. During the static unipedal posture, comparison of the CoPVm values within GPG was examined using the paired t-tests in EO and EC. Cohen's d ESs were computed. Two distinct two-way ANOVAs with repeated measures applied to explore the effect of the factors group (GPG versus CG) and vision (EO versus EC) on CoPVm values during static unipedal stance. Furthermore, to examine CoPVm during bipedal posture, a three-way ANOVA [group (GPG versus CG) *vision (EO versus EC) *surface (firm versus foam)] with repeated measures was conducted. A post-hoc Bonferroni test was conducted for every significant principal factor and interaction. Using the partial eta-square, effect sizes (ES) for ANOVA were computed (ηp2). To assess the relationship of static postural control results to core stability, Pearson's correlation coefficients (r) were examined. The foundation for statistical analysis was provided by IBM SPSS® Statistics software version 26. For every test, the level of significance was set at p < 0.05.
3. Results
3.1. Participants
Table 1 provides an overview of the participants' characteristics. It was found that there were no significant differences between the two groups in overall characteristics. GPG players had significantly lower HAGOS subscale scores (p < 0.001) than CG players (Table 1).
Table 1.
Characteristics of the participants.
| CG (n = 42) | GPG (n = 42) | p | |
|---|---|---|---|
| Age (years) | 21.54 (2.58) | 21.16 (2.12) | 0.46 |
| BM (kg) | 72.69 (6.76) | 73.76 (7.31) | 0.48 |
| Height (m) | 1.77 (0.05) | 1.76 (0.05) | 0.40 |
| BMI (kg/m2) | 23.05 (2.00) | 23.66 (2.21) | 0.19 |
| Playing experience (years) | 6.11 (1.85) | 6.02 (1.31) | 0.64 |
| Exposure/week | |||
| Trainings | 4.19 (0.77) | 4.40 (0.82) | 0.15 |
| Matches | 0.95 (0.21) | 0.92 (0.26) | 0.15 |
| Clinical entities (n, %) | |||
| Adductor-related GP | – | 33 (78.60 %) | – |
| Adductor- in conjunction with inguinal-related GP | – | 9 (21.40 %) | – |
| Injured side (n, %) | |||
| Dominant | – | 16 (38.10 %) | – |
| Non-dominant | – | 26 (61.90 %) | – |
| Dominant side (n, %) | |||
| Right | 40 (95.20 %) | 37 (88.10 %) | – |
| Left | 2 (4.80 %) | 5 (11.90 %) | – |
| HAGOS | |||
| Pain | 100.00 (100.00–100.00) | 70.00 (64.37–72.50) | <0.001 |
| Symptoms | 100.00 (100.00–100.00) | 67.86 (63.38–78.57) | <0.001 |
| ADL | 100.00 (100.00–100.00) | 75.00 (60–00.85.53) | <0.001 |
| Sports/Rec | 100.00 (100.00–100.00) | 57.81 (40.62–63.28) | <0.001 |
| PA | 100.00 (100.00–100.00) | 50.00 (34.37–62.75) | <0.001 |
| QOL | 100.00 (100.00–100.00) | 58.75 (45.00–75.00) | <0.001 |
CG: control group; GPG: groin pain group; GP: groin pain; BM: body mass; BMI: body mass index; HAGOS: Hip and Groin Outcome Score; ADL: activities in daily living; Sport/Rec: physical function in sport and recreation; PA: participation in physical activities; QOL: hip and/or groin-related quality of life.
3.2. Postural control
GPG had significantly higher CoPVm than CG on the firm surface in the EC (2.66 [95 % CI: 0.86–3.67]; p < 0.01) and on the foam one (p < 0.001) in both EO (2.88 [95 % CI: 1.42–4.43]) and EC (5.88 [95 % CI: 2.66–9.10]) in the bipedal stance (significant effect of factor group [F = 19.344; p < 0.001; ηp2 = 0.19]). Removal of vision raised CoPVm significantly (p < 0.001) on firm and foam surfaces alike, and for both groups (significant effects of vision factor [F = 418.981; p < 0.001; ηp2 = 0.83], and significant vision*group [F = 10.054; p < 0.01; ηp2 = 0.10] and vision*surface [F = 132.223; p < 0.001; ηp2 = 0.61] interactions). CoPVm was significantly higher (p < 0.001) on foam surface than on firm surface under EO and EC conditions for the two groups (significant effect of the surface factor [F = 246.191; p < 0.001; ηp2 = 0.75], surface*group [F = 7.084; p < 0.01; ηp2 = 0.08] and surface*vision [F = 132.223; p < 0.001; ηp2 = 0.61] interactions). There was no significant effect of group*vision*surface (F = 1.150; ηp2 = 0.01) interaction on the CoPVm (Table 2).
Table 2.
Static postural control data in the bipedal stance for the control (CG) and groin pain (GPG) groups.
| CG (n = 42) | GPG (n = 42) | |||
|---|---|---|---|---|
| CoPvm(mm/s) | Firm surface | EO | 7.95 (1.79) | 8.74 (1.93) |
| EC | 9.73 (2.24)a | 12.00 (3.99)a,d | ||
| Foam surface | EO | 12.05 (2.75)b | 14.94 (3.87)b,c | |
| EC | 21.22 (5.89)a,b | 27.11 (8.69)a,b,c | ||
CoPvm: mean centre of pressure velocity; EO: eyes opened; EC: eyes closed.
a significant differences between EO and EC at p < 0.001.
b significant differences between firm and foam surfaces at p < 0.001.
c significant differences between groups at p < 0.001.
d significant differences between groups at p < 0.01.
In the unipedal stance, no significant differences existed in CoPVm between DL and NDL of the CG in EO (d = 0.07) and EC (d = 0.12) conditions. For the GPG, the CoPVm was was significantly greater (p < 0.001; d = 0.90) on IL versus NIL in EC. However, no significant difference (d = 0.14) was found between limbs in CoPVm in EO. Comparing IL and DL, CoPVm was significantly greater with IL than with DL in EC (12.54 [95 % CI: 4.27–20.80]; p < 0.01). No significant difference (2.75 [95 % CI: 1.09–6.61]) existed between the DL and IL in CoPVm in EO (significant effects of group factor [F = 8.338; p < 0.01; ηp2 = 0.09], group*vision interaction [F = 6.862; p < 0.01; ηp2 = 0.07]). No significant effects of group factor (F = 0.574; ηp2 = 0.007), and group*vision interaction (F = 0.190; ηp2 = 0.002) on the CoPVm when comparing NIL and DL. Vision removal significantly (p < 0.001) elevated CoPVm in the two groups (significant effect of the factor of vision [F = 443.652; p < 0.001; ηp2 = 0.84], [F = 377.384; p < 0.001; ηp2 = 0.82] when comparing IL and NIL to DL, respectively) (Table 3).
Table 3.
Static postural control data in the unipedal stance for the control (CG) and groin pain (GPG) groups.
| CG (n = 42) DL | CG (n = 42) NDL | GPG (n = 42) IL | GPG (n = 42) NIL | |
|---|---|---|---|---|
| CoPvm (mm/s) | ||||
| EO | 35.85 (7.43) | 36.06 (6.94) | 38.61 (10.11) | 37.10 (8.83) |
| EC | 70.28 (13.25) | 70.93 (13.57) | 82.82 (23.42)a,b,c | 73.12 (24.09)c |
CoPvm: mean centre of pressure velocity; DL: dominant limb; NDL: non-dominant limb; IL: injured limb; NIL: non-injured limb; EO: eyes opened; EC: eyes closed.
a Significant differences between the IL and NIL at p < 0.001.
b Significant differences between the IL and DL at p < 0.01.
c Significant differences between EO and EC at p < 0.001.
3.3. Core stability
When lying on the DL and NDL, the side bridge measurements showed no differences in the CG (d = 0.02). The endurance measurements of the side bridges on the IL and the NIL did not differ significantly, according to comparison within the GPG (d = 0.16). When comparing the two groups, the GPG had significantly lower (p < 0.001) endurance times for the side bridge on the IL (d = 1.90) and NIL (d = 1.75), trunk flexor (d = 3.21) and extensor (d = 3.23) tests compared to the CG (Table 4).
Table 4.
Core stability data in the control (CG) and groin pain (GPG) groups.
| CG (n = 42) | GPG (n = 42) | p | Mean difference (95 % confidence interval) | Cohen's d | |
|---|---|---|---|---|---|
| Flexor | 133.69 (27.19) | 62.38 (15.57) | <0.001 | 71.30 (61.65–80.96) | 3.21 |
| Extensor | 150.11 (31.28) | 70.14 (15.66) | <0.001 | 79.97 (69.17–90.77) | 3.23 |
| Side bridge DL/IL | 85.19 (19.46) | 53.28 (13.74) | <0.001a | 31.90 (24.57–39.23) | 1.90 |
| Side bridge NDL/NIL | 85.21 (19.54) | 55.40 (14.06) | <0.001b | 29.80 (22.43–37.18) | 1.75 |
DL: dominant limb; NDL: non-dominant limb; IL: injured limb; NIL: non-injured limb.
Significant difference between the side bridge while lying on DL and IL.
Significant difference between the side bridge while lying on DL and NIL.
3.4. Correlation
In both GPG and CG, no significant correlations between static postural control and core stability measures were observed (Table 5).
Table 5.
Correlation data of static postural balance and core stability in the control (CG) and groin pain (GP) groups.
| CG |
||||||||
|---|---|---|---|---|---|---|---|---|
| Bipedal firm |
Bipedal foam |
Unipedal EO |
Unipedal EC |
|||||
| EO | EC | EO | EC | DL | NDL | DL | NDL | |
| Core stability | ||||||||
| Flexor | r = −0.13 | r = −0.22 | r = −0.29 | r = −0.13 | r = −0.11 | r = −0.09 | r = −0.18 | r = −0.1 |
| p = 0.38 | p = 0.16 | p = 0.05 | p = 0.41 | p = 0.46 | p = 0.53 | p = 0.25 | p = 0.52 | |
| Extensor | r = 0.03 | r = −0.11 | r = −0.03 | r = −0.04 | r = 0.13 | r = 0.08 | r = 0.002 | r = 0.03 |
| p = 0.84 | p = 0.45 | p = 0.82 | p = 0.78 | p = 0.39 | p = 0.60 | p = 0.98 | p = 0.83 | |
| Side bridge DL | r = −0.14 | r = −0.22 | r = −0.28 | r = −0.12 | r = −0.18 | r = −0.16 | r = −0.13 | r = −0.04 |
| p = 0.36 | p = 0.15 | p = 0.07 | p = 0.44 | p = 0.22 | p = 0.28 | p = 0.39 | p = 0.78 | |
| Side bridge NDL | r = −0.12 | r = −0.24 | r = −0.05 | r = −0.15 | r = −0.20 | r = −0.16 | r = −0.10 | r = −0.03 |
| p = 0.44 | p = 0.12 | p = 0.72 | p = 0.31 | p = 0.18 | p = 0.29 | p = 0.49 | p = 0.81 | |
| GPG |
||||||||
|---|---|---|---|---|---|---|---|---|
| Bipedal firm |
Bipedal foam |
Unipedal EO |
Unipedal EC |
|||||
| EO | EC | EO | EC | IL | NIL | IL | NIL | |
| Core stability | ||||||||
| Flexor | r = 0.26 | r = 0.12 | r = 0.07 | r = 0.10 | r = −0.27 | r = 0.01 | r = −0.16 | r = −0.12 |
| p = 0.09 | p = 0.41 | p = 0.65 | p = 0.95 | p = 0.08 | p = 0.92 | p = 0.30 | p = 0.43 | |
| Extensor | r = −0.06 | r = −0.24 | r = −0.06 | r = −0.18 | r = −0.13 | r = −0.08 | r = −0.19 | r = −0.18 |
| p = 0.67 | p = 0.11 | p = 0.66 | p = 0.24 | p = 0.39 | p = 0.57 | p = 0.21 | p = 0.24 | |
| Side bridge IL | r = 0.09 | r = 0.03 | r = −0.11 | r = −0.17 | r = −0.27 | r = 0.07 | r = −0.07 | r = −0.12 |
| p = 0.56 | p = 0.84 | p = 0.47 | p = 0.28 | p = 0.08 | p = 0.63 | p = 0.62 | p = 0.42 | |
| Side bridge NIL | r = −0.21 | r = −0.19 | r = −0.16 | r = −0.24 | r = −0.22 | r = −0.10 | r = −0.28 | r = −0.21 |
| p = 0.16 | p = 0.22 | p = 0.30 | p = 0.11 | p = 0.14 | p = 0.48 | p = 0.07 | p = 0.17 | |
EO: eyes opened; EC: eyes closed; DL: dominant limb; NDL: non-dominant limb; IL: injured limb; NIL: non-injured limb.
4. Discussion
This study aimed to (i) assess static postural control and core stability in soccer players suffering from GP compared to their healthy peers and (ii) explore relationship between these two parameters. The primary results demonstrated that, in comparison to their peers, soccer players with GP exhibited static postural control impairments under challenging conditions in the bipedal stance (firm EC, and foam) and on the IL (EC). Furthermore, in comparison to their counterparts, they demonstrated reduced core stability. Our hypothesis was not supported by the data, which showed no relationship between static postural control and core stability in soccer players suffering from GP.
Data about static postural control partially support findings from another study that found that, in comparison to their peers, soccer players suffering from GP had poor static postural control in the bipedal stance on foam surface (EO-EC).7 Standing on a foam surface alters proprioceptive information from the ankle joints.18 As a result, the central nervous system has to rely further on proprioceptive information from additional joints, such as the lumbosacral region, to sustain correct postural balance.19 In healthy individuals, this system prioritizes the control of posture through proprioceptive signals originating from the paraspinal muscles instead of the ankle muscles.19 On that note, it is possible that our soccer players suffering from GP were unable to compensate for the effect of the instability created by the foam surface because of a potential alteration in the proprioceptors of the core. Accordingly, soccer players suffering from GP had a lower postural control on this surface than their healthy counterparts. Increased visual dependence is a possible response to proprioceptive or vestibular disorders.20 Our soccer players suffering from GP revealed static postural control disorders in bi- and unipedal stances when vision was unavailable. This could reinforce our previous hypothesis that these players depended more on vision for maintaining static postural control than healthy players. From this point of view, our soccer players suffering from GP may have, in addition to the lower core endurance observed, a deficit in core proprioception.
It has been thought that various musculoskeletal systems, such as neuromuscular control, proprioception, strength and endurance of the core, interact to ensure optimal stability.21, 22, 23, 24 Separate tests are used to assess the different elements ensuring core stability.25 Performance in one test does not predict performance in other tests assessing this parameter. 26 It could be therefore assumed that the data obtained in terms of core muscle endurance do not reflect core proprioceptive acuity in soccer players suffering from GP. This could account for the absence of correlation between measures of static postural control and core endurance in our soccer players suffering from GP. Further investigation of the relationship between core proprioception and static postural control in these players is important to either verify or reject this assumption.
On the basis of the above considerations, no association was found between measures of core stability and static postural control in our soccer players suffering from GP. Considering the static postural control importance in this practice, understanding its impairment in further research is crucial to designing an optimal rehabilitation strategy in this area. These results provide information on the direction of future studies exploring the mechanisms underlying deficits in static postural control in soccer players suffering from GP.
This study has certain limitations. Trunk endurance tests were chosen to assess core stability because they are easy, cheap and the most reliable measure of core stability. Future studies are needed to evaluate other components of core stability, specifically, proprioception, and to analyze the relationship of static postural control and core proprioception in soccer players suffering from GP.
5. Conclusion
Soccer players suffering from non-time-loss GP exhibited poor static postural control in bipedal stance (firm and foam EC) and when standing on IL (EC), compared to their healthy peers. Additionally, no correlations between static postural control and core stability were observed among these players.
Ethical approval
This study was approved by the local Ethics Committee from the High Institute of Nursing, University of Sfax, Tunisia (CPP/SUD, approval number: 0206/2019).
Patient consent statement
Prior to enrollment, all participants gave their written informed consent.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Data statement
The data that support the findings of this study are available from the corresponding author, FC, upon reasonable request.
Guardian/patient's consent
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F098
I confirm that I have read and understood the subject information sheet for the study and have had the opportunity to ask questions which have been answered fully.
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F098
I understand that participation is voluntary and I am free to withdraw at any time, without giving any reason, without medical care or legal rights being affected.
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F098
The compensation arrangements have been discussed with me.
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F098
I understand that I will be given a copy of this consent form.
CRediT authorship contribution statement
Abderrahmane Rahmani: Supervision, Writing – review & editing. Haithem Rebai: Investigation, Supervision. Thouraya Fendri: Investigation. Sébastien Boyas: Supervision, Writing – review & editing. Sonia Sahli: Supervision, Writing – review & editing.
Declaration of interest statement
All authors have no financial affiliation (including research funding) or involvement with any commercial organization that has a direct financial interest in any matter included in this manuscript. All authors declare no conflicts of interest.
Acknowledgments
Authors would like to thank all the soccer players who participated in this study and for all their contributions to the work.
Footnotes
GP = groin pain.
GPG = GP group.
CG = control group.
Contributor Information
Fatma Chaari, Email: chaarifatma94@gmail.com.
Abderrahmane Rahmani, Email: Abdel.Rahmani@univ-lemans.fr.
Haithem Rebai, Email: haithem.rebai@yahoo.fr.
Thouraya Fendri, Email: thourayafendri1@gmail.com.
Sébastien Boyas, Email: Sebastien.Boyas@univ-lemans.fr.
Sonia Sahli, Email: sonia.sahli@isseps.usf.tn.
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