
==== Front
Int J Sports Phys Ther
Int J Sports Phys Ther
2159
International Journal of Sports Physical Therapy
2159-2896
NASMI Website: International Journal of Sports Physical Therapy

35949380
36631
10.26603/001c.36631
Original Research
Effects of a Groin Pain Prevention Program in Male High School Soccer Players: A Cluster-Randomized Controlled Trial
https://orcid.org/0000-0002-1420-603X
Fujisaki Kazuki 1
https://orcid.org/0000-0003-2110-205X
Akasaka Kiyokazu 2
https://orcid.org/0000-0003-0503-9214
Otsudo Takahiro 2
https://orcid.org/0000-0003-4355-3222
Hattori Hiroshi 2
https://orcid.org/0000-0003-3697-8265
Hasebe Yuki 3
https://orcid.org/0000-0003-4461-7259
Hall Toby 4
1 Saitama Medical University Graduate School of Medicine; Department of Physical Therapy, Ota College of Medical Technology
2 Saitama Medical University Graduate School of Medicine; School of Physical therapy, Saitama Medical University
3 Saitama Medical University Graduate School of Medicine; Department of Rehabilitation, Saitama Medical Center, Saitama Medical University
4 Curtin School Allied Health, Curtin University; Manual Concepts, Perth
Corresponding author: Dr. Kiyokazu Akasaka, Saitama Medical University 981 Kawakado, Moroyama, Saitama 350-0495, Japan. E-mail: akasaka-smc@umin.ac.jp
1 8 2022
2022
17 5 841850
22 12 2021
14 4 2022
© The Author(s)
https://creativecommons.org/licenses/by-nc/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (4.0) which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited.

Background

Groin pain is frequently reported by soccer players. A prevention program incorporating the Copenhagen adduction exercise (CAE) has been shown effective in decreasing adductor muscle injury in semi-professional soccer players. However, the effect of such programs on groin pain in high school soccer players is unknown. No reports have examined the effects of combining the CAE with other targeted exercises such as the Nordic hamstrings exercise (NHE).

Purpose

To evaluate the preventative effects of exercise on groin pain in high school soccer players in three groups comprising NHE alone, combined NHE and CAE, and a control group.

Design

Randomized Controlled Clinical Trial.

Methods

A cluster randomized controlled trial spanning 16 weeks was conducted on 202 high school soccer players from seven high schools in a Japanese under 18 Soccer League. Players were allocated to either group A (three schools, 66 players) receiving the CAE alone, or group B (two schools, 73 players) receiving the CAE and NHE, or control group C (two schools, 63 players) who performed their usual training. This study compared the number of injuries, injury rate, and severity of the injury of groin pain in these three groups.

Results

The number of players injured was less in group B (4 players) compared to C (18 players), and time-lost to soccer was less in groups A (6 players) and B (3 players) compared to group C (16 players). Injury rates were significantly lower in groups A and B, with the relative risk of injury compared to group C of 0.42 (95% CI 0.19% to 0.90%) in group A and 0.19 (95% CI 0.07 to 0.54) in group B.

Conclusion

A 16-week program incorporating the CAE in training sessions in high school soccer players reduced the incidence of groin pain and which may be related to injury severity according to time -lost to soccer, however the combination of both the CAE and NHE may be more effective than the CAE alone.

Level of Evidence

2b

Groin pain
Copenhagen adduction exercise
Nordic hamstrings exercise
Injury prevention
High school
Soccer
==== Body
pmcINTRODUCTION

Soccer is a sport that requires high-intensity sprinting, kicking, and rapid changes in direction at high speed,1–4 which can be important causes of injury.5 It has been reported that in soccer, the most common injuries are to muscle, particularly the hamstrings and adductor longus.6

Injury surveys of soccer players show that groin pain is relatively common and accounts for 11% of all injuries.7 In addition, 55% of male soccer players are reported to have experienced groin pain in the past.8 Groin pain in soccer players is typically caused by kicking or running,9 and is associated with adductor muscle weakness.10 Furthermore, most groin pain in soccer players has been reported to be minor to moderate with no time loss related to training or games.11

With respect to groin pain, the Doha agreement classifies pain into adductor-related, iliopsoas-related, inguinal-related, pubic-related, and hip joint-related pain.12 Adductor-related pain is considered to be the most common category accounting for 61% of all groin pain,13 and the most frequent cause in soccer players.14

The incidence of groin pain can be reduced by up to 41% through groin pain prevention programs such as the Copenhagen adduction exercise (CAE) in semi-professional soccer players.15 Despite this, there is a lack of information on the effects of injury prevention programs in younger soccer players. Functionally, the hamstring muscles have an auxiliary effect on the hip adductor muscles.16,17 Both muscle groups have been shown to demonstrate high activity during kicking, jumping, and cutting movements that occur specifically in soccer.18 Despite this, it is unclear whether training the hamstring muscles enhances the effect of the CAE in groin pain injury prevention.

Therefore, the purpose of this study was to evaluate the preventative effects of exercise on groin pain in high school soccer players in three groups comprising NHE alone, combined NHE and CAE, and a control group.

METHODS

Study design and participants

Participants were male high school students participating in a Japanese under 18 soccer leagues. Participants were competing at the highest level in the prefecture and national league, and the top teams were targeted. We contacted 10 schools with teams in this league for potential inclusion. Consent was obtained from the principal and coach from each school. Following such approval all parents and players were required to provide written informed consent. All rights of the participants were protected. This study followed the Declaration of Helsinki and was approved by the University Ethics Committee at the Saitama Medical University, Saitama, Japan (M-98).

Randomization

This cluster randomized controlled trial was registered with the University Hospital Medical Information Network at The University of Tokyo Hospital (Registration number 000036863) and was conducted from August 2019 to December 2019. The authors determined it would be difficult to blind subjects through individual subject randomization, so each high school team formed a cluster group which were then randomized using the envelope method. After a team agreed to participate, the principal investigator opened a sealed envelope revealing their group assignment. Group A received the CAE alone, group B received the CAE and NHE, and group C received no interventions other than continuing their normal practice. The group randomization procedure used is not considered optimum in randomized clinical trials. However, this procedure is widely used and accepted in sports injury prevention trials as a way to limit contamination between intervention and control groups.15 In addition, each school insisted that any intervention must be offered to team members as a group rather than as individuals. Two high schools that did not respond, one high school that could not start at the right time, and four others absent from club activities for some reason were excluded.

Blinding

It was not possible to blind players, coaches or the principal investigator to group allocation. Recorded data with encrypted numbers were collected by the principal investigator alone. However, the research assistant was not informed of the randomization, and outcome measures were not available to any party until all data had been collected.

Intervention

The CAE was performed as follows. The athlete lay on their side, their forearm on the ground to stabilize the trunk, while their other arm was placed with their hand on their pelvis. A team mate supported the player’s uppermost leg at the ankle and knee. The athlete was then required to lift their body off the ground, by adducting their upper hip, until the upper leg and trunk were horizontal, following which they lifted their lower leg off the ground to touch ankles. This was counted as one repetition, each lasting three seconds. (Figure 1).19 Based on previous studies,20,21 players were instructed to stop if they experienced more than 3/10 pain while performing the exercise. For the CAE, players were asked to carry out the exercise program 1-3 times a week for 16 weeks as part of their regular warm-up.

93182 Figure 1. The Copenhagen adduction exercise.

Starting/ending position, (B) The mid position of the adductor muscle strengthening program.

For the NHE, the player started in a high kneeling position with their lower legs stabilized by an assistant. The player then slowly lowered their body until parallel with the ground. The exercise was completed once their hands touched the ground (Figure 2).22 Again, if pain of greater than 3/10 was provoked during the exercise the player was told to stop. For the NHE, players were asked to carry out the exercise program 1-3 times a week for 16 weeks as part of their regular warm-up.

93183 Figure 2. The Nordic hamstrings exercise.

Starting position, (B) End position of the Hamstrings muscle strengthening program.

The number of repetitions was based on previously reported effective injury prevention programs (Table 1).15,22 The principal investigator explained the exercises to the coach, athletic trainer, and athletes before commencement of the study. During the intervention, the researchers visited each team once a week to observe the exercises and give advice if necessary. Subjects were informed that the exercise had to be conducted under the supervision of a coach or athletic trainer, and that the principal investigator was to be contacted if problems or adverse events occurred during the exercise program.

93181 Table 1. Training protocol for Copenhagen adduction exercise (CAE) and Nordic hamstring exercise (NHE)

	Week	Weekly sessions	Sets (per side)*	Repetitions (per side)*	
CAE	1	2	1	3-5	
	2	3	1	3-5	
	3-4	3	1	7-10	
	5-16	3	1	12-15	
NHE	1	1	2	5	
	2	2	2	6	
	3	2	3	6	
	4	2	3	6,7,8	
	5-16	2	3	8,9,10	
*CAE describes the number and number of sets on one side.

Compliance

Exercise compliance was recorded daily by athletes on a recording sheet. To calculate overall compliance, the total number of completed sessions was summed and divided by the number of respondents. Once a week, we contacted managers, athletic trainers, and athlete representatives to keep track of exercise progress. The principal investigator collected recording papers with encrypted numbers.

Outcome measures

The intervention period was 16 weeks. Data collection sheets were distributed to athletes and completed by individuals to record their exercise compliance and injuries. Any presentation or development of groin pain was conveyed to the athletic trainer or physiotherapist. The details of the injury were self-reported, but when the athlete was uncertain about what to report, he was advised by an athletic trainer or physiotherapist, who was informed of the details by the chief investigator. Reports were collected weekly by the principal investigator. The definition of groin pain in this study was a condition in which pain occurs in the groin during sports activities, regardless of time loss or need for treatment, with reference to previous studies.23,24

The principal investigator explained the Doha classification method to the trainers and physiotherapists of each team and let them determine the type of groin pain for each athlete in pain. The number of injuries and the injury rate indicates the frequency and probability of groin pain. The analysis was performed using an intention-to-treat (ITT) analysis.

Exposure

To calculate the exposure time individually, the athletes were asked to record daily practice time, match time, and time lost due to injury, and the total for each group was summed for each category. Once a week, managers, athletic trainers, and athlete representatives were contacted, and worked closely with the researchers to review the status of the recording and injury report forms. The principal investigator entered and matched the data from record sheet with personal information.

Sample size

The sample size calculation was based on the average prevalence of all groin problems among male football players (29%).25 On the basis of these data, a groin pain rate for this study of 29% in the group C, 17% in the intervention group A, and 12% in the intervention group B was projected. Using these rates, the sample size to determine statistically significant differences by using cluster randomization as well as a 2-tailed test with α = .05 and 1-β = .80 was calculated. The estimated sample size for this study thus obtained was 189 (63 patients per group).

Statistical analyses

χ2 test was performed to compare the number of injuries to groin pain among the three groups A, B, and C. Following that, Bonferroni correction was performed as a post-hoc analysis for the items for which a significant difference was found. The injury rate per 1000 hours was calculated from the number of injuries. Relative risk (RR) was calculated to show the risks of developing groin pain for groups A and B relative to group C. Injury severity was determined by counting the calendar days lost because of the groin pain. Groin pain was classified as minor (1-7 days lost), moderate (8-21 days lost), or severe (more than 21 days lost), with reference to previous studies.23,24 The effect size for the effect size of the number of injuries was calculated as φ. Effect size <0.1 is rated as small, 0.3 rated medium, and >0.5 rated large.26 IBM SPSS Statistics for Windows, Version 26.0 (Armonk, NY: IBM Corp Released 2018) was used for statistical analysis.

RESULTS

Participants

A total of seven high school soccer clubs (202 players) were enrolled in the study. The flow of the players through the phases of the study is shown in Figure 3. There was a total of 11 dropouts, four in Group A, one in Group B, and six in Group C. The reasons were retirement, injury, and low compliance. Baseline characteristics for players included in the ITT analysis are shown in Table 2.

93184 Figure 3. Flowchart showing numbers of players participating.

93185 Table 2. Subject Characteristics (N=202)

	Group A (N=66)†	Group B (N=73)†	Group C (N=63)†	p-⁠value	
Age (years)*	16.4±0.9 (15－18)	16.0±0.7 (15－18)	16.1±0.9 (15－18)	0.47	
Height (cm)*	170.7±5.7 (156.0－186.3)	169.2±5.2 (157.2－184.0)	170.3±5.1 (160.0－180.0)	0.24	
Weight (kg)*	60.2±7.1 (40－83)	58.4±7.2 (42－80)	58.5±6.5 (45－74)	0.39	
Dominant foot (players)				0.22	
Right	55	67	52		
Left	11	6	11		
Field position (players)				0.74	
Attackers	10	12	11		
Midfielders	24	27	23		
Defenders	26	23	24		
Goalkeepers	6	11	5		
*The minimum-maximum is listed.

†Group A Copenhagen adduction exercise alone. Group B combined Copenhagen adduction exercise and Nordic hamstrings exercise. Group C continues as usual.

Number of injuries

Table 3 shows the number of cases with groin pain. The frequency of groin pain during the intervention period was significantly lower in group B than in group C. The number of players with groin pain who lost time due to injury was significantly less in groups A and B than in group C.

When comparing groups, A and B, a small effect size was observed in groin pain, although there was no significant difference.

The injury rate of groin pain and relative risk with time lost to sport

Table 4 shows the groin pain injury rate and the injury rate with time lost RR. The incidence of groin pain per 1000 hours was lower in groups A and B than in group C. Furthermore, RR of groin pain was significantly lower in groups A and B than that in group C according to the 95% confidence intervals. The injury rate for groin pain with time lost per 1000 hours was lower in groups A and B than in group C. Furthermore, RRs of groin pain and groin pain with time lost per 1000 hours were significantly lower in groups A and B than that in group C according to the 95% confidence intervals.

Severity of groin pain

Table 5 shows the severity of reported groin pain (mild, moderate, or severe). The average number of days lost was 5.5 ± 5.2 days in group A, 10.3 ± 6.4 days in group B, and 14.4 ± 8.3 days in group C. The rate of minor groin pain in the intervention groups was higher than in the control group (66% in group A vs 33% in group B vs 25% in group C), whereas the rate of moderate groin pain was lower in the intervention group than in the control group (33% in group A vs 66% in group B vs 68% in group C).

Fisher’s exact test was used to determine if there was a significant difference in the distribution of injury severity between both groups (group A and B vs group C). However, due to the low number of players with groin pain in the moderate and severe categories, these categories were combined into one category. No difference was detected in the severity of groin pain between groups (p = 0.21).

93186 Table 3. Frequency of groin pain by number of groin pain injuries*

	Group A†
(n=66)	Group B†
(n=73)	Group C†
(n=63)	χ2 test
p-value	Group A vs
Group B	Group A vs
Group C	Group B vs
Group C	Post-hoc‡	
p- value	Effect size(φ)	p- value	Effect size(φ)	p- value	Effect size(φ)	
No.of injuries (%)	
Groin pain	8 (12.1)	4 (5.5)	18 (28.6)	0.01	0.16	0.12	0.02	0.20	0.01	0.31	B<C	
Time-lost-to-sports
groin pain	6 (9.1)	3 (4.1)	16 (25.4)	0.01	0.24	0.10	0.01	0.22	0.01	0.30	A.B<C	
*A χ2 test was performed to compare the three groups. The two groups were then compared using the χ2 test or Fisher’s exact test. †Group A= Copenhagen adduction exercise alone. Group B= combined intervention of Copenhagen adduction exercise and Nordic hamstrings exercise. Group C= control group. ‡The Bonferroni correction was used as a post hoc test.

93187 Table 4. Injury rate of groin pain and relative risk with time lost to sport

	No. of injuries	Injury rate/
1000 competition hours	Relative risk of injury rate	
Group A*	Group B*	Group C*	Group A*	Group B*	Group C*	B/A†	95%CI‡	A/C§	95%CI‡	B/C**	95%CI‡	
Groin pain	8	4	18	0.64	0.25	1.24	0.93	0.84 - 1.03	0.42	0.19 - 0.90††	0.19	0.07 - 0.54††	
Time-lost-to-sports
groin pain	6	3	16	0.48	0.19	1.10	0.95	0.87 - 1.04	0.36	0.15 - 0.86††	0.16	0.05 - 0.53††	
*Group A= Copenhagen adduction exercise alone. Group B= combined intervention of Copenhagen adduction exercise and Nordic hamstrings exercise. Group C= continues as usual. The competition hours of groups A, B, and C were 12424.0, 16159.0, 14505.0, respectively. †B/A indicates the ratio of group B to group A. ‡95%CI: 95% confidence interval. §A/C indicates the ratio of group A to group C. **B/C indicates the ratio of group B to group C. ††There was a significant difference in the 95% confidence interval. (P < .05)

93188 Table 5. Distribution of groin pain by severity (categorized by days lost)*

		A group†		B group†		C group†		
	n	%		n	%		n	%	Total (n)	
Groin pain	Minor	4	66.7		1	33.3		4	25.0	9	
	Moderate	2	33.3		2	66.7		11	68.8	15	
	Severe	0	0		0	0		1	6.2	1	
	Total (n)	6			3			12		25	
*There were no significant differences in the severity of groin pain between the three groups. Due to the low number of injuries, minor injuries were compared to the category that combined moderate and severe injuries. Fisher’s exact test, p = 0.21.

†Group A= Copenhagen adduction exercise alone. Group B= combined intervention of Copenhagen adduction exercise and Nordic hamstrings exercise. Group C= continues as usual.

Compliance with the exercise program

The CAE compliance rate was 97% in group A and 95% in group B. The NHE compliance rate was 98% in group B.

DISCUSSION

The CAE has been reported to reduce the incidence of groin pain,15 which is consistent with the findings of the current study. In this study, the combined intervention of CAE and NHE reduced the number of injuries, and CAE alone reduced the number of cases with time lost to sport as shown in Tables 3 and 4. This supports the effectiveness of CAE in preventing groin pain in high school soccer players. The results also indicate that CAE and NHE were effective in preventing severe groin pain. From these results, it is likely that the NHE enhances the effect of the CAE. One explanation for this is that the adductor muscle and the hamstrings also assist in hip adductor, and conversely, adductor muscles also assist in hip extension,16,17 so it is possible that NHE enhanced the effect of CAE through this mechanism. Another explanation is combining exercises together likely had an enhanced strengthening effect on the adductor and hamstring muscle groups which reduced the occurrence and severity of injury. From the above, the combination of CAE and NHE exercises may be more effective in preventing groin pain than CAE alone.

In a report of factors related to the occurrence of groin pain and reduction in physical function in professional soccer players, it was reported that isometric strength of the adductor muscle is an important factor.10 The CAE has been shown to improve both eccentric adductor and eccentric abductor muscle strength.17 In addition, it has been reported that muscle damage in the thigh is reduced by the stability of the trunk,27,28 and it is possible that a combination of CAE and NHE programs may increase resistance to injury by increasing the extensibility and stability of soft tissues, including muscles, on the anterior, posterior, medial, and lateral sides of the hip joint and trunk. Since this study did not measure trunk stability or motor control, additional studies from such a viewpoint should be conducted in the future.

Kicking is important in soccer, and during this movement, the adductor muscles show maximum tension from the position of hip extension to flexion in the swing phase.29 In addition, the hamstring muscle are highly active during maximal hip and knee extension and flexion,30 suggesting a potential for injury. From this, it is predicted that the adductor and hamstrings muscles are likely to work strongly together at the same time, and that the hamstrings act cooperatively with the adductor muscle in the hip flexion phase. Strengthening both groups of muscles may enable greater protection during kicking activities which may be effective to prevent pain.

One of the goals of this study was to determine whether a muscle strengthening exercise program utilizing the CAE alone or a combined intervention including the CAE and NHE would reduce the severity of groin pain. The effect of the CAE intervention on groin pain severity has not been previously reported. Previous studies were used to assess severity.31 The results of this study found that CAE and NHE did not affect the severity of groin pain. Specifically, it did not reduce the average number of days lost and did not affect the intensity of groin pain development, which was classified as mild, moderate, or severe. Interestingly, the rate of minor groin pain was greater in the intervention groups vs the control group yet the overall injury rate was lower in the intervention group vs the control. One interpretation of this discrepancy is that CAE reduces the severity of groin pain, so that there are more minor injuries. A similar finding has been reported for the NHE in reducing the severity of hamstring injuries.32 The number of cases categorized according to higher severity of injury is small in the current study, hence further study is required to determine the effect of CAE on injury severity.

Comparing intervention groups, A and B, the number of groin pain injuries was lower in group B. Furthermore, the injury rate was lower in group B than in group A, but there was no significant difference in RR. Both groups A and B had a significantly reduced risk of injury compared to group C. This suggests that both forms of exercise may be effective in reducing the incidence of injury, although the CAE alone appears to influence the risk of injury.

Limitations

This research was conducted using a cluster randomized controlled trial. Even with the mixed-effects statistical analysis that attempts to account for this clustering, this design can result in high Type I error rates. Also, the results may include Type II errors due to the limited sample size. Since the research was targeted only at top-team high school soccer players, it may have led to a selection bias. Also, all injuries were self-reported, which can lead to measurement bias, and results may vary if all injuries were diagnosed by a healthcare professional. Interventions for inguinal pain prevention exercises were limited to 16 weeks, so it is essential to examine the effects of these exercises over a longer period. In addition, a larger and more diverse sample would help to better understand the impact of CAE and NHE on injury rate and loss time.

CONCLUSION

A 16-week program incorporating the CAE in training sessions in high school soccer players reduced the incidence of groin pain and severity of injury according to time-lost to soccer, however the combination of both the CAE and NHE may be more effective than the CAE alone.

Conflicts of interest

The authors report no conflicts of interest.

Acknowledgements

The authors thank all players and coaches who participated in the study, as well as the team medical staff.
==== Refs
The effect of two speed endurance training regimes on performance of soccer players PLoS One Iaia F.M. Fiorenza M. Perri E.. 22 9 2015
10 9 e0138096 10.1371/journal.pone.0138096.
The effects of short term detraining and retraining on physical fitness in elite soccer players PLoS One Joo C.H. 10 5 2018
13 5 e0196212 10.1371/journal.pone.0196212.
Effects and sustainability of a 13-day high-intensity shock microcycle in soccer J Sports Sci Med Wahl P. Güldner M. Mester J. 2014
13 259 265 24790477
Chronic ingestion of sodium and potassium bicarbonate, with potassium, magnesium and calcium citrate improves anaerobic performance in elite soccer players Nutrients Chycki Jakub Golas Artur Halz Mateusz Maszczyk Adam Toborek Michal Zajac Adam MDPI AG 1 11 2018
10 11 1610 2072-6643 10.3390/nu10111610 10.3390/nu10111610 30388775
Injuries in professional male soccer players in the netherlands: a prospective cohort study Journal of Athletic Training Stubbe Janine H. van Beijsterveldt Anne-Marie M. C. van der Knaap Sissi Stege Jasper Verhagen Evert A. van Mechelen Willem Backx Frank J. G. 1 2 2015
50 2 211 216 1062-6050 10.4085/1062-6050-49.3.64 10.4085/1062-6050-49.3.64 25531144
Epidemiology of muscle injuries in professional football (soccer) The American Journal of Sports Medicine Ekstrand Jan Hägglund Martin Waldén Markus 18 2 2011
39 6 1226 1232 0363-5465 10.1177/0363546510395879 10.1177/0363546510395879
A prospective epidemiological study of injuries in four English professional football clubs British Journal of Sports Medicine Hawkins R. D. Fuller C. W. 1 6 1999
33 3 196 203 0306-3674 10.1136/bjsm.33.3.196 10.1136/bjsm.33.3.196 10378073
Groin pain and soccer players: male versus female occurrence J Phys Fit Sports Med Karlsson M.K. Dahan R. Magnusson H. 2014
54 487 493
Diagnosis of acute groin injuries. A prospective study of 110 athletes The American Journal of Sports Medicine Serner Andreas Tol Johannes L. Jomaah Nabil Weir Adam Whiteley Rodney Thorborg Kristian Robinson Matthew Hölmich Per 14 5 2015
43 8 1857 1864 0363-5465 10.1177/0363546515585123 10.1177/0363546515585123
Intrinsic risk factors for groin injuries among male soccer players The American Journal of Sports Medicine Engebretsen Anders Hauge Myklebust Grethe Holme Ingar Engebretsen Lars Bahr Roald SAGE Publications 10 8 2010
38 10 2051 2057 0363-5465 10.1177/0363546510375544 10.1177/0363546510375544
Time before return to play for the most common injuries in professional football: a 16-year follow-up of the UEFA Elite Club Injury Study British Journal of Sports Medicine Ekstrand Jan Krutsch Werner Spreco Armin van Zoest Wart Roberts Craig Meyer Tim Bengtsson Håkan 2020
54 7 421 426 0306-3674 10.1136/bjsports-2019-100666 10.1136/bjsports-2019-100666 31182429
Doha agreement meeting on terminology and definitions in groin pain in athletes British Journal of Sports Medicine Weir Adam Brukner Peter Delahunt Eamonn Ekstrand Jan Griffin Damian Khan Karim M Lovell Greg Meyers William C Muschaweck Ulrike Orchard John Paajanen Hannu Philippon Marc Reboul Gilles Robinson Philip Schache Anthony G Schilders Ernest Serner Andreas Silvers Holly Thorborg Kristian Tyler Timothy Verrall Geoffrey de Vos Robert-Jan Vuckovic Zarko Hölmich Per BMJ 6 2015
49 12 768 774 0306-3674 10.1136/bjsports-2015-094869 10.1136/bjsports-2015-094869 26031643
Epidemiology of time loss groin injuries in a men’s professional football league: a 2-year prospective study of 17 clubs and 606 players British Journal of Sports Medicine Mosler Andrea B Weir Adam Eirale Cristiano Farooq Abdulaziz Thorborg Kristian Whiteley Rod J Hӧlmich Per Crossley Kay M 2018
52 5 292 297 0306-3674 10.1136/bjsports-2016-097277 10.1136/bjsports-2016-097277 28666981
Multidisciplinary assessment of 100 athletes with groin pain using the doha agreement: high prevalence of adductor-related groin pain in conjunction with multiple causes Clin J Sport Med Taylor Rachel Vuckovic Zarko Mosler Andrea Agricola Rintje Otten Roald Jacobsen Philipp Holmich Per Weir Adam 7 2018
28 4 364 369 1050-642X 10.1097/jsm.0000000000000469 10.1097/jsm.0000000000000469 28654441
The adductor strengthening programme prevents groin problems among male football players: a cluster-randomised controlled trial British Journal of Sports Medicine Harøy Joar Clarsen Benjamin Wiger Espen Guldahl Øyen Mari Glomnes Serner Andreas Thorborg Kristian Hölmich Per Andersen Thor Einar Bahr Roald 2019
53 3 145 152 0306-3674 10.1136/bjsports-2017-098937 10.1136/bjsports-2017-098937
The adductor magnus “mini-hamstring”: MRI appearance and potential pitfalls Skeletal Radiology Broski Stephen M. Murthy Naveen S. Krych Aaron J. Obey Mitchel R. Collins Mark S. Springer Science and Business Media LLC 2016
45 2 213 219 0364-2348 10.1007/s00256-015-2291-5 10.1007/s00256-015-2291-5 26554947
Anatomy of the adductor magnus origin implications for proximal hamstring injuries Orthop J Sports Med Obey M.R. Broski S.M. Spinner R.J.. 2016
4 2325967115625055 10.1177/2325967115625055. 26798764
Groin pain and muscular imbalance of quadriceps and hamstrings in an elite soccer player - a case study Sportverletzung · Sportschaden Ludwig O. Kelm J. 4 8 2016
30 3 163 167 0932-0555 10.1055/s-0042-110249 10.1055/s-0042-110249 27490356
Large eccentric strength increase using the copenhagen adduction exercise in football: A randomized controlled trial Scandinavian Journal of Medicine & Science in Sports Ishøi L. Sørensen C. N. Kaae N. M. Jørgensen L. B. Hölmich P. Serner A. Wiley 2016
26 11 1334 1342 0905-7188 10.1111/sms.12585 10.1111/sms.12585 26589483
Copenhagen five-second squeeze: a valid indicator of sports-related hip and groin function British Journal of Sports Medicine Thorborg K Branci S Nielsen M P Langelund M T Hölmich P 2017
51 7 594 599 0306-3674 10.1136/bjsports-2016-096675 10.1136/bjsports-2016-096675 27935487
Five-second squeeze testing in 333 professional and semiprofessional nale ice hockey players: how are hip and groin symptoms, strength, and sporting function related? Orthopaedic Journal of Sports Medicine Wörner Tobias Thorborg Kristian Eek Frida 1 2 2019
7 2 232596711982585 2325-9671 10.1177/2325967119825858 10.1177/2325967119825858 30815497
A 10-week randomized trial comparing eccentric vs. concentric hamstring strength training in well-trained soccer players Scandinavian Journal of Medicine and Science in Sports Mjølsnes Roald Arnason Arni Østhagen Tor Raastad Truls Bahr Roald 10 2004
14 5 311 317 0905-7188 10.1046/j.1600-0838.2003.367.x 10.1046/j.1600-0838.2003.367.x
Consensus statement on injury definitions and data collection procedures in studies of football (soccer) injuries Br J Sports Med Fuller C.W. Ekstrand J. Junge A.. 2006
40 3 193 201 10.1136/bjsm.2005.025270 16505073
Soccer injury in the lower extremities Br J Sports Med Wong P. Hong Y. 2005
39 473 82 10.1136/bjsm.2004.015511. 16046325
Groin problems in male soccer players are more common than previously reported The American Journal of Sports Medicine Harøy Joar Clarsen Ben Thorborg Kristian Hölmich Per Bahr Roald Andersen Thor Einar SAGE Publications 1 2 2017
45 6 1304 1308 0363-5465 10.1177/0363546516687539 10.1177/0363546516687539
Statistical Power Analysis for the Behavioral Sciences Cohen J. Routledge Academic New York, NY, USA 1988

Core-muscle training and neuromuscular control of the lower limb and trunk J Athl Train Sasaki Shizuka Tsuda Eiichi Yamamoto Yuji Maeda Shugo Kimura Yuka Fujita Yuki Ishibashi Yasuyuki 1 9 2019
54 9 959 969 1062-6050 10.4085/1062-6050-113-17 10.4085/1062-6050-113-17 31386583
Core stability training for injury prevention Sports Health: A Multidisciplinary Approach Huxel Kellie C. Anderson Barton E. 25 3 2013
5 6 514 522 1941-7381 10.1177/1941738113481200 10.1177/1941738113481200 24427426
Adductor longus mechanics during the maximal effort soccer kick Sports Biomechanics Charnock Brian L. Lewis Cara L. Garrett William E., Jr. Queen Robin M. 9 2009
8 3 223 234 1476-3141 10.1080/14763140903229500 10.1080/14763140903229500 19891200
Extremity muscle activation and alignment during the soccer instep and side-foot kicks Journal of Orthopaedic & Sports Physical Therapy Brophy Robert H. Backus Sherry I. Pansy Brian S. Lyman Stephen Williams Riley J. 5 2007
37 5 260 268 0190-6011 10.2519/jospt.2007.2255 10.2519/jospt.2007.2255 17549955
International Olympic Committee consensus statement: Methods for recording and reporting of epidemiological data on injury and illness in sport 2020 (including STROBE Extension for Sport Injury and Illness Surveillance (STROBE-SIIS)) British Journal of Sports Medicine Bahr Roald Clarsen Ben Derman Wayne Dvorak Jiri Emery Carolyn A Finch Caroline F Hägglund Martin Junge Astrid Kemp Simon Khan Karim M Marshall Stephen W Meeuwisse Willem Mountjoy Margo Orchard John W Pluim Babette Quarrie Kenneth L Reider Bruce Schwellnus Martin Soligard Torbjørn Stokes Keith A Timpka Toomas Verhagen Evert Bindra Abhinav Budgett Richard Engebretsen Lars Erdener Uğur Chamari Karim BMJ 18 2 2020
54 7 372 389 0306-3674 10.1136/bjsports-2019-101969 10.1136/bjsports-2019-101969 32071062
Effects of nordic hamstring exercise on hamstring injuries in high school soccer players: a randomized controlled trial International Journal of Sports Medicine Hasebe Yuki Akasaka Kiyokazu Otsudo Takahiro Tachibana Yomei Hall Toby Yamamoto Mitsuru 5 1 2020
41 3 154 160 0172-4622 10.1055/a-1034-7854 10.1055/a-1034-7854
