Physical Therapy in Sport
1. Introduction
Strategies to reduce sports injury risk include identifyingathletes with characteristics indicative of greater risk of injury andimplementing specific training programs to alter these characteristicsand reduce injury risk (Meeuwisse, 1994). Prior to theestablishment of a relationship between a proposed factor andinjury risk, the choice of characteristics to use in the screening ofathletes is often based on reasonable assumptions about deficits inperformance or movement patterns and a particular injury, whichare subsequently trialled in prospective cohort studies in whichpotential injury risk factors are measured and athletes followedover time (Finch, 2006; Murphy, Connolly, & Beynnon, 2003). Thefirst step in the development of such screening procedures is toestablish that the methods used to evaluate potential injury risk factors are reliable prior to conducting prospective studies (Gabbe,Bennell, Wajswelner, & Finch, 2004).The reliability of a test is the reproducibility of the measurementvalues over multiple test sessions and has the following characteristics.With repeated assessments on multiple people there is nochange in the means of the sessions (differences may indicatelearning effects), there is small within-subject variation over thesessions, and there is a high test-retest correlation among thesessions (Hopkins, 2000). Hopkins recommends a minimum ofthree measurement trials on different days for assessment of reliability.It is also important that the population used for the determinationof reliability is representative of the population to be usedfor subsequent investigation.Since the 1990s there has been an increasing emphasis onfunctional movement tests as candidate assessments for injury riskscreening (Cordova & Armstrong, 1996). Jumping and landing taskshave commonly been used (Walsh, Ford, Bangen, Myer, & Hewett,2006). Side-to-side strength imbalance has also attracted interestover recent times (Askling, Karlsson, & Thorstensson, 2003; Croisier,Forthomme, Namurious, Van-Derthommen, & Crielaard, 2002;Negrete, Schick, & Cooper, 2007; Newton et al., 2006; Orchard,Marsden, Lord, & Garlick, 1997; Yamamoto, 1993) both as a performanceindicator and/or injury risk factor. However, publishedevidence of the reliability of many of these types of tests is lackingor insufficient. Studies have investigated the performance reliabilityof the countermovement vertical jump (Aragon-Vargas,2000; Arteaga, Dorado, Chavarren, & Calbet, 2000; Carlock et al.,2004; Markovic, Dizdar, Jukic, & Cardinale, 2004; Moir, Sanders,Button, & Glaister, 2005), drop vertical jump (Walsh et al., 2006)and single-leg vertical jump (Cordova & Armstrong, 1996; Flanagan& Harrison, 2007; Gustavsson et al., 2006; Newton et al., 2006;Risberg, Holm, & Ekeland, 1995) but there are no reliability data forsingle-leg drop jumps or maximum side-spring tests.Few studies (Arteaga et al., 2000; Gustavsson et al., 2006) haveperformed more than two trials to demonstrate reliability, andmany (Carlock et al., 2004; Flanagan & Harrison, 2007; Markovicet al., 2004; Walsh et al., 2006) have used only single sessions, withmultiple trials within that session. Of the investigations establishingreliability across more than two trials, Arteaga (Arteaga et al.,2000) reported negligible learning effects for double-leg countermovementjumps and drop jumps using a contact mat measurementdevice, and Gustavsson (Gustavsson et al., 2006) reportedsingle-leg vertical jump tests using a laser timing device as reliable(ICC: 0.89–0.97). Risberg (Risberg et al., 1995) concluded that thesingle-leg countermovement vertical jump measured using a Vertecmeasurement device had too much variation to be recommended(CV ¼ 7.0% dominant, 7.7% non-dominant), using a twotrial test-retest design.The protocols used for establishing the reliability of jump-basedtests may also vary substantially. For example, jumps may be performedwith hands on hips, hands free, or from differing dropheights, use different measurement techniques such as contactmats, lasers, force plates, or Vertec, and perform different types ofjumps such as countermovement, drop, single or double-legvertical jumps. It is desirable that injury risk screening protocols aredeveloped that are easily performed and measured, cost effectiveand use portable equipment in order to increase their utility withlarger numbers of athletes.Assessment of movement patterns by kinematic analysis iswidely advocated for injury risk factor evaluation. Three-dimensionalkinematic analysis is the gold standard (McLean et al., 2005)but this limits the number of athletes that can be tested efficientlyand cost-effectively. With a move towards real world screening oflarger numbers of athletes, two-dimensional analysis is portable,more time efficient and cost effective. Two-dimensional movementanalysis has been validated against three-dimensional analysis forseveral functional movement tests (McLean et al., 2005), howeverlittle is known regarding the reliability of these movement testsacross multiple sessions using two-dimensional analysis.To date, only the reliability of the double-leg drop jump test hasbeen reported using two-dimensional analysis (McLean et al.,2005). With jumping and landing tasks common in functional andperformance screening for locomotion-based team sport athletes;and dynamic valgus movements suggested as the major mechanismfor ACL injury (Olsen, Mykleburst, Engebretsen, & Bahr, 2004),investigation of the two-dimensional medial/lateral knee actionsduring these movements for further use in large scale prospectivetesting is warranted.The purpose of this study was to investigate the reliability of sixsimple movement tasks in which an objective performancemeasure and two-dimensional movement pattern recordings wereobtained simultaneously. The tests are easily performed, and theequipment used is easily operated, cost effective and portable.These tests could potentially form a battery of lower extremityassessment tools to be used in building a lower extremity profile ofathletes during pre and mid season screening, or for prospectivepre-season screening.