You are currently viewing The Hip in Ice Hockey Part 5: How to Design the Optimal Hip Screening Protocol and Identify At-Risk Athletes

The Hip in Ice Hockey Part 5: How to Design the Optimal Hip Screening Protocol and Identify At-Risk Athletes

Designing and implementing testing and monitoring procedures to identify athletes who are at increased risk for suffering hip-related pathology is crucial for sustained, high-level, ice hockey performance.

Overview

First, understanding the relationship between of multiplanar hip strength, motion, and how they operate in more complex, functional tasks, are of paramount importance for identifying athletes who are “at risk” of sustaining a new non-contact injury. A recent extensive review of the research regarding testing and management of athletes with groin pain was done by Thorborg and colleagues (2018), if interested [1]. Although beyond the scope of this article, it’s important to note that imaging plays a role in detecting serious pathology in athletes presenting with pain or dysfunction and may, in some cases, also serve to give more credence to the diagnostic work-up process if it matches clinical signs and symptoms [1]. I will focus on physical screening and monitoring strategies for determination of at-risk athletes, in effort to prevent and/or alleviate common hip-related pathology.

In case you’re late to the party and missed Part 1-4 of this comprehensive article series, you can view them hereherehere, and here.

Part 1: How non-contact injuries occur in sport and why well-functioning hips are necessary for elite ice hockey performance.

Part 2: Prevalence of hip injures in ice hockey, how and to whom they occur, with a special focus on groin strains.

Part 3: Review of where groin pain may actually be coming from (spoiler alert: it may not be from the groin muscles)

Part 4: The financial cost of injury for NHL players, and the potential costs to sustained high-level performance and long-term health.

I strongly advise taking the time to go through each of these articles, at some point. I intentionally broke up this article series into many parts to make the content of each article more easily digestible.

The FMS and Injury Prediction

 Pre-participation screening exams have been developed in an effort to identify athletes who may be at increased risk for sustaining subsequent injuries. Despite the Functional Movement Screen (FMS) being the most prevalent standardized screening tool available, it has been consistently shown to be a poor predictor of injury risk in athletes [2-4]. Although its intra-rater reliability (degree of agreement among repeated test administrations) and inter-rater reliability (degree of agreement between different practitioners conducting the test) are generally quite good [5-7], the prognostic accuracy of the FMS was only slightly better than flipping a coin for correctly classifying Division II athletes most at risk for subsequent injury  [4]. In this study, the FMS composite score was used to predict injury risk. This is the most commonly evaluated FMS metric, and it appears to lack injury predictability. When using the FMS as a tool to identify at-risk athletes, research suggests that it may be wise to focus on asymmetry identified in one or more of the FMS tests to help pinpoint athletes that have increased injury susceptibility [8, 9], as opposed to concentrating on the FMS composite score.

3.jpg

Specific to ice hockey, the FMS has failed to show adequate clinical utility to identify those at risk for injury in youth [10], male NCAA Division I [11], men’s junior [11, 12], or East Coast Hockey League (ECHL) players [13]. Although the FMS may be a valuable tool for practitioners in a variety of contexts, current data suggests that it has limited, if any, capacity for injury risk identification in ice hockey athletes. Through this analysis, I’m not trying to discredit the FMS; it certainly has value in many different settings. For example, as I noted above, it’s a great standardized tool for evaluating asymmetry, which may help identify at-risk athletes. However, I would choose a more time-efficient protocol that may have better translation to ice hockey athletes.

The SEBT and Y-Balance Test

The Star Excursion Balance Test (SEBT) is a reliable measure and a valid dynamic test to predict risk of lower extremity injury, to identify dynamic balance deficits in patients with lower extremity conditions, and to be responsive to training programs in healthy participants and those with lower extremity conditions [14]. The SEBT is a series of single-limb squats using the nonstance limb to reach maximally to touch a point on the ground, and includes 8 reaching directions [15]. The Y-Balance is essentially a modified (i.e. condensed) version of the SEBT, using 3 reaching directions instead of 8 [16]. Although very similar tests, it’s important to note that there appear to be slightly different outcomes between the two when reaching in the forward direction [17, 18]. Therefore, using data from one test to insinuate performance on the other is not an advisable approach. Here are images of the 3 Y-Balance Test reaching directions, A) Anterior, B) Posteromedial, and C) Posterolateral:

Y-Balance (1).jpg

There’s conflicting evidence as to whether athletes with groin pain have ROM impairments, compared with controls [19-23], but evaluating hip ROM may be able to distinguish those with femoroacetabular impingement (FAI) from those without [24]. Performance on the Y-Balance Test has been associated with hip flexion ROM [25], hip extension strength and hip internal rotation ROM [26], lower body flexibility asymmetry [27], hip abduction function and strength [28, 29], risk factors for ACL tears [30] and readiness to return to sport after ACL surgery [31], and lower body injury risk [31-42]. A recent meta-analysis determined that a composite reach score difference of less than 94% of limb length and an anterior reach difference of 4 cm or greater between limbs may be predictors for increased injury risk in athletes [38]. There is also research conducted in large athletic cohorts that found no correlation between Y-Balance Test performance and injury risk [43, 44]. It’s clear that sport injuries are multifactorial; using a single test alone, such as the Y-Balance, to screen for injury risk in athletes, is not an advisable approach.

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I believe that integration of a standardized screening regime requiring single-leg balance, multi-joint coordination, motor control, ROM, and a minor degree of lower body strength, is a time-efficient way to evaluate multiple athletic components and asymmetries in ice hockey athletes (and other athletes who spend most of their time on a single leg). The Y-Balance Test (or SEBT) is an example of one of these multifaceted tests, and there’s a significant body of research supporting its use for identifying, or at least aiding in the identification of athletes at increased risk for injury.

Manual Muscle Testing to Assess Hip Strength

In Part 1, I discussed the unique contribution of hip musculature for producing on-ice locomotion, including on-ice acceleration and sprinting prowess [45-51]. In Part 2, we discovered how lack of absolute hip adduction strength and/or lack of hip adduction relative to hip abduction strength, may increase risk for sustaining a groin injury [19, 52-58]. In addition to the hips, the importance of the abdominal muscles cannot be overstated. The integration of the hip and abdominal muscles plays a significant role in appropriate pelvic positioning during various intricate skating movements, as well as successful performance in explosive rotational movements integral to ice hockey, such as shooting, passing, and quick turning [54]; this concept is discussed in greater detail in Part 3.

The importance of collecting objective hip strength measurements is obvious to many. Manual muscle testing (MMT) is often used for this collection [60]. Although no equipment aside from a hand-held dynamometer is necessary, the way that hip strength is tested using this simple device must be considered. An isometric squeeze test can be done, but this is typically performed bilaterally. There appear to be differences in force-generating capabilities between bilateral and unilateral movements [61-63], which could potentially impact the results.

The hand-held dynamometer, itself, has been used since the 1940’s [60] and is a reliable tool for assessing hip muscle strength [64]. However, standardization of the protocol is of paramount importance to ensure consistent measurement criteria. I can’t stress this point enough. Lack of standardization can result in data misrepresentation in a variety of ways, including through strength/style differences among practitioners and variance in athlete testing positions. For example, Thorborg et al. (2013) found that female testers consistently produced lower values compared with their male tester counterparts [65]. This suggests that the values recorded using hand-held dynamometry depend on the resistance offered by the assessor. Light et al. (2016) found differences in hip strength values between long-lever (i.e. when measured from the ankle) and short-lever (i.e. when measured from below the knee) positions [66]. Measuring an athlete at different anatomical points will undoubtedly misrepresent changes in their hip strength. Here is an image of manual muscle testing (MMT) of side-lying hip adduction via Harøy et al. (2017), [67]:

4.JPG
Image from: Harøy et al. (2017). Including the copenhagen adduction exercise in the FIFA 11+ provides missing eccentric hip adduction strength effect in male soccer players: A randomized controlled trial. ?AJSM?, ?45?(13), pp.3052-3059.

Hand-held dynamometers have been used to assess eccentric strength (“break testing”) and isometric testing (“make testing”). High correlations generally exist between the two methods [68, 69], but strength values are typically higher during break (eccentric strength) testing [68, 70]. Break (eccentric strength) testing may be the superior method when it comes to groin pain identification [55]. However, make (isometric strength) testing has advantages of (1) being more reliable [71] and (2) producing less stress on the musculoskeletal system, which could minimize testing-induced injury risk and delayed onset muscle soreness from the testing [55, 72]. Additionally, resistance placed at long-lever positions (i.e. by the ankles) appears to be a better predictor of previous groin pathology, compared with resistance placed at short-lever positions (i.e. slightly below the knees) during testing [66, 73, 74]. Above all else, the standardization of measurement protocols is of utmost importance. Hébert and colleagues suggest that the following aspects of protocol administration should be strongly considered [71]:

  • The same tester should be used for all measurements, if possible.
  • The participants should be stabilized while measuring muscle strength.
  • Hip flexion should be measured in the standing or supine position.
  • Hip extension is best measured in the standing or prone standing positions; the prone position is not recommended.
  • Internal and external rotation are more reliably measured in hip flexion

I’ve come up with a few suggestions based on the literature reviewed on hip strength testing. First and foremost, I advise using a device that provides objective data and a standardized procedure for data collection to minimize measurement error and promote reliable, longitudinal results. Using dynamometry or a sphygmomanometer are both great options. However, a new device by Vald Performance, the GroinBar, has recently shown greater measurement precision than either of these two methods [75]. The GroinBar is far more expensive than the former two methods, but is a very high-quality product and has the benefit of not being dependent on practitioner skill/strength. You can learn more above the GroinBar here. Please note that I’m not affiliated with this company or device in any way.

Here are my thoughts on specific positions for hip strength testing:

  • Unilateral 90-degree (short-lever) supine hip flexion*
  • Unilateral 0-degree (long-lever) supine hip adduction*
  • Unilateral 0-degree (long-lever) supine hip abduction*
  • Unilateral 90-degree (short-lever) supine hip internal rotation
  • Unilateral 90-degree (short-lever) supine hip external rotation
  • Unilateral 0-degree (long-lever) prone hip extension
  • Metrics of primary interest, given the current body of research

Summary

An applicable screening tool that provides objective data should be used in conjunction with a standardized procedure that is sensitive enough to identify athletes who are “at risk” of sustaining a new non-contact injury. Evaluating hip movement and strength capabilities are of principal importance for identification of these athletes, particularly in the sport of ice hockey. There are a multitude of testing/screening methods out there; the ideal method for you will depend on many factors, including available resources, budget, time, and athlete cohort. In the next article (Part 6), I’ll review the research on how to treat different types of hip pain and briefly discuss the potential impact of early sport specialization on FAI risk in ice hockey athletes.

UPDATE: Part 6 has been released and can be viewed here.


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Reference

  1. Thorborg, K., Reiman, M.P., Weir, A., Kemp, J.L., Serner, A., Mosler, A.B. and Hölmich, P., 2018. Clinical examination, diagnostic imaging, and testing of athletes with groin pain: an evidence-based approach to effective management. journal of orthopaedic & sports physical therapy, 48(4), pp.239-249.
  2. Moran, R.W., Schneiders, A.G., Mason, J. and Sullivan, S.J., 2017. Do Functional Movement Screen (FMS) composite scores predict subsequent injury? A systematic review with meta-analysis. Br J Sports Med, pp.bjsports-2016.
  3. Whittaker, J.L., Booysen, N., De La Motte, S., Dennett, L., Lewis, C.L., Wilson, D., McKay, C., Warner, M., Padua, D., Emery, C.A. and Stokes, M., 2017. Predicting sport and occupational lower extremity injury risk through movement quality screening: a systematic review. Br J Sports Med, 51(7), pp.580-585.
  4. Dorrel, B., Long, T., Shaffer, S. and Myer, G.D., 2018. The functional movement screen as a predictor of injury in National Collegiate Athletic Association Division II athletes. Journal of athletic training, 53(1), pp.29-34.
  5. Parenteau-G, E., Gaudreault, N., Chambers, S., Boisvert, C., Grenier, A., Gagné, G. and Balg, F., 2014. Functional movement screen test: A reliable screening test for young elite ice hockey players. Physical Therapy in Sport, 15(3), pp.169-175.
  6. McCunn, R., aus der Fünten, K., Fullagar, H.H., McKeown, I. and Meyer, T., 2016. Reliability and association with injury of movement screens: A critical review. Sports Medicine, 46(6), pp.763-781.
  7. Cuchna, J.W., Hoch, M.C. and Hoch, J.M., 2016. The interrater and intrarater reliability of the functional movement screen: A systematic review with meta-analysis. Physical Therapy in Sport, 19, pp.57-65.
  8. Chalmers, S., Fuller, J.T., Debenedictis, T.A., Townsley, S., Lynagh, M., Gleeson, C., Zacharia, A., Thomson, S. and Magarey, M., 2017. Asymmetry during preseason Functional Movement Screen testing is associated with injury during a junior Australian football season. ?Journal of science and medicine in sport?, ?20?(7), pp.653-657.
  9. Mokha, M., Sprague, P.A. and Gatens, D.R., 2016. Predicting musculoskeletal injury in National Collegiate Athletic Association Division II athletes from asymmetries and individual-test versus composite functional movement screen scores. ?Journal of athletic training?, ?51?(4), pp.276-282.
  10. Avery, M., 2017. Seasonal changes in functional fitness and neurocognitive performance in youth ice hockey players (Doctoral dissertation).
  11. Vert, N., 2016. The Relationship between Low Functional Movement Screen Scores, Injury History and the Rate of Injury in Collegiate and Junior Hockey Players (Doctoral dissertation, University of Nebraska at Omaha).
  12. Dossa, K., Cashman, G., Howitt, S., West, B. and Murray, N., 2014. Can injury in major junior hockey players be predicted by a pre-season functional movement screen–a prospective cohort study. The Journal of the Canadian Chiropractic Association, 58(4), p.421.
  13. Perry, J., 2015. Correlations Between the Functional Movement Screen (FMS), the Balance Error Scoring System (BESS), and Injury.
  14. Gribble, P.A., Hertel, J. and Plisky, P., 2012. Using the Star Excursion Balance Test to assess dynamic postural-control deficits and outcomes in lower extremity injury: a literature and systematic review. Journal of athletic training, 47(3), pp.339-357.
  15. Gribble, P., 2003. The star excursion balance test as a measurement tool. Athletic Therapy Today, 8(2), pp.46-47.
  16. Plisky, P.J., Gorman, P.P., Butler, R.J., Kiesel, K.B., Underwood, F.B. and Elkins, B., 2009. The reliability of an instrumented device for measuring components of the star excursion balance test. North American journal of sports physical therapy: NAJSPT4(2), p.92.
  17. Fullam, K., Caulfield, B., Coughlan, G.F. and Delahunt, E., 2014. Kinematic analysis of selected reach directions of the Star Excursion Balance Test compared with the Y-Balance Test. Journal of sport rehabilitation23(1), pp.27-35.
  18. Coughlan, G.F., Fullam, K., Delahunt, E., Gissane, C. and Caulfield, B.M., 2012. A comparison between performance on selected directions of the star excursion balance test and the Y balance test. Journal of athletic training47(4), pp.366-371.
  19. Kloskowska, P., Morrissey, D., Small, C., Malliaras, P. and Barton, C., 2016. Movement patterns and muscular function Before and after onset of sports-related groin pain: a systematic review with meta-analysis. ?Sports Medicine?, ?46?(12), pp.1847-1867.
  20. Tak, I., Engelaar, L., Gouttebarge, V., Barendrecht, M., Van den Heuvel, S., Kerkhoffs, G., Langhout, R., Stubbe, J. and Weir, A., 2017. Is lower hip range of motion a risk factor for groin pain in athletes? A systematic review with clinical applications. Br J Sports Med, 51(22), pp.1611-1621.
  21. Nepple, J.J., Goljan, P., Briggs, K.K., Garvey, S.E., Ryan, M. and Philippon, M.J., 2015. Hip strength deficits in patients with symptomatic femoroacetabular impingement and labral tears.Arthroscopy,? 31?(11),? pp.2106-2111.
  22. ?Freke, M.D., Kemp, J., Svege, I., Risberg, M.A., Semciw, A. and Crossley, K.M., 2016. Physical impairments in symptomatic femoroacetabular impingement: a systematic review of the evidence. ?Br J Sports Med?, pp.bjsports-2016.
  23. Mosler, A.B., Weir, A., Hölmich, P. and Crossley, K.M., 2015. Which factors differentiate athletes with hip/groin pain from those without? A systematic review with meta-analysis. ?Br J Sports Med?, ?49?(12), pp.810-810.
  24. Diamond, L.E., Dobson, F.L., Bennell, K.L., Wrigley, T.V., Hodges, P.W. and Hinman, R.S., 2014. Physical impairments and activity limitations in people with femoroacetabular impingement: a systematic review. ?Br J Sports Med?, pp.bjsports-2013.
  25. Robinson, R. and Gribble, P., 2008. Kinematic predictors of performance on the Star Excursion Balance Test. ?Journal of sport rehabilitation?, ?17?(4), pp.347-357.
  26. McCann, R.S., Kosik, K.B., Terada, M., Beard, M.Q., Buskirk, G.E. and Gribble, P.A., 2017. Associations Between Functional and Isolated Performance Measures in College Women’s Soccer Players. ?Journal of sport rehabilitation?, ?26?(5), pp.376-385.
  27. Overmoyer, G.V. and Reiser, R.F., 2015. Relationships between lower-extremity flexibility, asymmetries, and the Y balance test. ?The Journal of Strength & Conditioning Research?, ?29?(5), pp.1240-1247.
  28. Kivlan, B.R. and Martin, R.L., 2012. Functional performance testing of the hip in athletes: a systematic review for reliability and validity. ?International journal of sports physical therapy?, 7?(4), p.402.
  29. Wilson, B.R., Robertson, K.E., Burnham, J.M., Yonz, M.C., Ireland, M.L. and Noehren, B., 2017. The Relationship Between Hip Strength and the Y-Balance Test. ?Journal of sport rehabilitation?, pp.1-24.
  30. Lee, M., Sim, S. and Jiemin, Y., 2017. Y-Balance Test but Not Functional Movement Screen Scores Are Associated with Peak Knee Valgus Moments During Unplanned Sidestepping: Implications for Assessing Anterior Cruciate Ligament Injury Risk. ISBS Proceedings Archive35(1), p.104.
  31. Garrison, J.C., Bothwell, J.M., Wolf, G., Aryal, S. and Thigpen, C.A., 2015. Y balance test™ anterior reach symmetry at three months is related to single leg functional performance at time of return to sports following anterior cruciate ligament reconstruction. ?International journal of sports physical therapy?, ?10?(5), p.602.
  32. ?Gonell, A.C., Romero, J.A.P. and Soler, L.M., 2015. Relationship between the Y balance test scores and soft tissue injury incidence in a soccer team. ?International journal of sports physical therapy?, ?10?(7), p.955.
  33. Plisky, P.J., Rauh, M.J., Kaminski, T.W. and Underwood, F.B., 2006. Star Excursion Balance Test as a predictor of lower extremity injury in high school basketball players. ?Journal of Orthopaedic & Sports Physical Therapy?, ?36?(12), pp.911-919.
  34. Butler, R.J., Lehr, M.E., Fink, M.L., Kiesel, K.B. and Plisky, P.J., 2013. Dynamic balance performance and noncontact lower extremity injury in college football players: an initial study. Sports health?, ?5?(5), pp.417-422.
  35. Gribble, P.A., Hertel, J. and Plisky, P., 2012. Using the Star Excursion Balance Test to assess dynamic postural-control deficits and outcomes in lower extremity injury: a literature and systematic review. ?Journal of athletic training?, ?47?(3), pp.339-357.
  36. Steffen, K., Emery, C.A., Romiti, M., Kang, J., Bizzini, M., Dvorak, J., Finch, C.F. and Meeuwisse, W.H., 2013. High adherence to a neuromuscular injury prevention programme (FIFA 11+) improves functional balance and reduces injury risk in Canadian youth female football players: a cluster randomised trial. ?Br J Sports Med?, pp.bjsports-2012.
  37. ?Dallinga, J.M., Benjaminse, A. and Lemmink, K.A., 2012. Which screening tools can predict injury to the lower extremities in team sports?. ?Sports medicine?, ?42?(9), pp.791-815.
  38. Hegedus, E.J., McDonough, S.M., Bleakley, C., Baxter, D. and Cook, C.E., 2015. Clinician-friendly lower extremity physical performance tests in athletes: a systematic review of measurement properties and correlation with injury. Part 2—the tests for the hip, thigh, foot and ankle including the star excursion balance test. ?Br J Sports Med?, ?49?(10), pp.649-656.
  39. Wright, A.A., Dischiavi, S.L., Smoliga, J.M., Taylor, J.B. and Hegedus, E.J., 2017. Association of Lower Quarter Y-Balance Test with lower extremity injury in NCAA Division 1 athletes: an independent validation study. Physiotherapy, 103(2), pp.231-236.
  40. Pollock, K.M., 2010. The star excursion balance test as a predictor of lower extremity injury in high school football players.
  41. Hartley, E.M., Hoch, M.C. and Boling, M.C., 2018. Y-balance test performance and BMI are associated with ankle sprain injury in collegiate male athletes. Journal of science and medicine in sport, 21(7), pp.676-680.
  42. Stiffler, M.R., Bell, D.R., Sanfilippo, J.L., Hetzel, S.J., Pickett, K.A. and Heiderscheit, B.C., 2017. Star Excursion Balance Test anterior asymmetry is associated with injury status in Division I collegiate athletes. journal of orthopaedic & sports physical therapy, 47(5), pp.339-346.
  43. Lai, W.C., Wang, D., Chen, J.B., Vail, J., Rugg, C.M. and Hame, S.L., 2017. Lower Quarter Y-Balance Test Scores and Lower Extremity Injury in NCAA Division I Athletes. Orthopaedic journal of sports medicine, 5(8), p.2325967117723666.
  44. Smith, J., DePhillipo, N., Kimura, I., Kocher, M. and Hetzler, R., 2017. Prospective functional performance testing and relationship to lower extremity injury incidence in adolescent sports participants. ?International journal of sports physical therapy?, ?12?(2), p.206.
  45. Bracko, M.R., 2004. Biomechanics powers ice hockey performance. Biomechanics, 2004, pp.47-53.
  46. Marino, G.W., 1983. Selected mechanical factors associated with acceleration in ice skating. Research quarterly for exercise and sport, 54(3), pp.234-238.
  47. Renaud, P.J., Robbins, S.M., Dixon, P.C., Shell, J.R., Turcotte, R.A. and Pearsall, D.J., 2017. Ice hockey skate starts: a comparison of high and low calibre skaters. Sports Engineering, 20(4), pp.255-266.
  48. Bizzini, M., Notzli, H.P. and Maffiuletti, N.A., 2007. Femoroacetabular impingement in professional ice hockey players: a case series of 5 athletes after open surgical decompression of the hip. The American journal of sports medicine, 35(11), pp.1955-1959.
  49. Keogh, M.J. and Batt, M.E., 2008. A review of femoroacetabular impingement in athletes. Sports Medicine, 38(10), pp.863-878.
  50. Philippon, M.J., Weiss, D.R., Kuppersmith, D.A., Briggs, K.K. and Hay, C.J., 2010. Arthroscopic labral repair and treatment of femoroacetabular impingement in professional hockey players. The American journal of sports medicine, 38(1), pp.99-104.
  51. Kuhn, A.W., Noonan, B.C., Kelly, B.T., Larson, C.M. and Bedi, A., 2016. The hip in ice hockey: A current concepts review. Arthroscopy, 32(9), pp.1928-1938.
  52. Tyler, T.F., Nicholas, S.J., Campbell, R.J. and McHugh, M.P., 2001. The association of hip strength and flexibility with the incidence of adductor muscle strains in professional ice hockey players. The American journal of sports medicine, 29(2), pp.124-128.
  53. Whittaker, J.L., Small, C., Maffey, L. and Emery, C.A., 2015. Risk factors for groin injury in sport: an updated systematic review. Br J Sports Med, pp.bjsports-2014.
  54. Merrifield, H.H. and Cowan, R.F., 1973. Groin strain injuries in ice hockey: A disparity in muscle strength between both hip joint adductor muscle groups was found to be a contributing factor in groin strain injuries. The Journal of sports medicine, 1(2), pp.41-42.
  55. Thorborg, K., Serner, A., Petersen, J., Madsen, T.M., Magnusson, P. and Hölmich, P., 2011. Hip adduction and abduction strength profiles in elite soccer players: implications for clinical evaluation of hip adductor muscle recovery after injury. The American journal of sports medicine, 39(1), pp.121-126.
  56. Delahunt, E., Fitzpatrick, H. and Blake, C., 2017. Pre-season adductor squeeze test and HAGOS function sport and recreation subscale scores predict groin injury in Gaelic football players. Physical therapy in sport, 23, pp.1-6.
  57. Ryan, J., DeBurca, N. and Mc Creesh, K., 2014. Risk factors for groin/hip injuries in field-based sports: a systematic review. Br J Sports Med, pp.bjsports-2013.
  58. Malliaras, P., Hogan, A., Nawrocki, A., Crossley, K. and Schache, A., 2009. Hip flexibility and strength measures: reliability and association with athletic groin pain. ?British Journal of Sports Medicine?, ?43?(10), pp.739-744.
  59. Rennie, W.J. and Lloyd, D.M., 2017. Sportsmans Groin: The Inguinal Ligament and the Lloyd Technique. ?Journal of the Belgian Society of Radiology?, ?101?(S2).
  60. Reiman, M.P. and Thorborg, K., 2014. CLINICAL EXAMINATION AND PHYSICAL ASSESSMENT OF HIP JOINT-RELATED PAIN IN ATHLETES. ?International journal of sports physical therapy?, ?9?(6), p.737
  61. Rejc, E., Lazzer, S., Antonutto, G., Isola, M. and Di Prampero, P.E., 2010. Bilateral deficit and EMG activity during explosive lower limb contractions against different overloads. European journal of applied physiology, 108(1), p.157.
  62. Kuruganti, U. and Murphy, T., 2008. Bilateral deficit expressions and myoelectric signal activity during submaximal and maximal isometric knee extensions in young, athletic males. European journal of applied physiology, 102(6), pp.721-726.
  63. Matkowski, B., Martin, A. and Lepers, R., 2011. Comparison of maximal unilateral versus bilateral voluntary contraction force. European journal of applied physiology, 111(8), pp.1571-1578.
  64. Thorborg, K., Petersen, J., Magnusson, S.P. and Hölmich, P., 2010. Clinical assessment of hip strength using a hand-held dynamometer is reliable. ?Scandinavian journal of medicine & science in sports?, ?20?(3), pp.493-501.
  65. Thorborg, K., Bandholm, T., Schick, M., Jensen, J. and Hölmich, P., 2013. Hip strength assessment using handheld dynamometry is subject to intertester bias when testers are of different sex and strength. ?Scandinavian journal of medicine & science in sports?, ?23?(4), pp.487-493.
  66. Light, N. and Thorborg, K., 2016. The precision and torque production of common hip adductor squeeze tests used in elite football. Journal of science and medicine in sport, 19(11), pp.888-892.
  67. Harøy, J., Thorborg, K., Serner, A., Bjørkheim, A., Rolstad, L.E., Hölmich, P., Bahr, R. and Andersen, T.E., 2017. Including the copenhagen adduction exercise in the FIFA 11+ provides missing eccentric hip adduction strength effect in male soccer players: A randomized controlled trial. ?The American journal of sports medicine?, ?45?(13), pp.3052-3059.
  68. Stratford, P.W. and Balsor, B.E., 1994. A comparison of make and break tests using a hand-held dynamometer and the Kin-Com. ?Journal of Orthopaedic & Sports Physical Therapy?, ?19?(1), pp.28-32.
  69. ? Bohannon, R.W., 1990. Hand-held compared with isokinetic dynamometry for measurement of static knee extension torque (parallel reliability of dynamometers). ?Clinical Physics and Physiological Measurement?, ?11?(3), p.217
  70. Bohannon, R.W., 1988. Make tests and break tests of elbow flexor muscle strength. Physical therapy,? 68?(2),? pp.193-194.
  71. Hébert, L.J., Maltais, D.B., Lepage, C., Saulnier, J., Crête, M. and Perron, M., 2011. Isometric muscle strength in youth assessed by hand-held dynamometry: A feasibility, reliability, and validity study: A feasibility, reliability, and validity study. ?Pediatric Physical Therapy?, ?23?(3), pp.289-299.
  72. Mayne, E., Memarzadeh, A., Raut, P., Arora, A. and Khanduja, V., 2017. Measuring hip muscle strength in patients with femoroacetabular impingement and other hip pathologies: A systematic review. ?Bone and Joint Research?, ?6?(1), pp.66-72.
  73. Hölmich, P., Uhrskou, P., Ulnits, L., Kanstrup, I.L., Nielsen, M.B., Bjerg, A.M. and Krogsgaard, K., 1999. Effectiveness of active physical training as treatment for long-standing adductor-related groin pain in athletes: randomised trial. ?The Lancet?, ?353?(9151), pp.439-443.
  74. Drew, M.K., Palsson, T.S., Izumi, M., Hirata, R.P., Lovell, G., Chiarelli, P., Osmotherly, P.G. and Graven-Nielsen, T., 2016. Resisted adduction in hip neutral is a superior provocation test to assess adductor longus pain: an experimental pain study. ?Scandinavian journal of medicine & science in sports?, ?26?(8), pp.967-974.
  75. Ryan, S., Kempton, T., Pacecca, E. and Coutts, A.J., 2018. Measurement Properties of an Adductor Strength Assessment System in Professional Australian Footballers. International journal of sports physiology and performance, pp.1-13.