Lower extremity pathomechanics during high impact activity, such as directional changes, landing, and deceleration, have been associated with increased risk of injury in athletes playing team sports (Griffin et al., 2006; Hewett et al., 2005), especially in young female athletes (Myer et al., 2013). One of the most common lower extremity high risk movements described in the literature is dynamic valgus, which is associated with anterior cruciate ligament (ACL) injury (Hewett et al., 2005) and, patellofemoral pain (Myer et al., 2010). Female athletes exhibit a 4- to 6-fold increase in incidence of ACL injuries compared to male athletes (Arendt and Dick, 1995). The mechanism underlying this gender disparity in ACL injury incidence is likely multi-factorial (Elliot et al., 2010; Hewett et al., 2010). Intrinsic risk factors for ACL injury include anatomic, hormonal, and neuromuscular abnormalities (Griffin et al., 2006). Of these factors, aberrant neuromuscular control is modifiable and thus provides direction for targeted neuromuscular training with high-risk individuals (Hewett et al., 2010).
Video analyses have revealed four common motor performance components that potentially contribute to non-contact ACL injury in female athletes during landing (Hewett et al., 2010): 1) knees collapse medially upon landing, 2) the injured knee is near full extension at landing, 3) most if not all of the athlete's weight is supported on a single limb, and 4) the trunk tends to be flexed laterally at landing. While these same components are observed in male athletes, they are more pronounced in female athletes (Alentorn-Geli et al., 2009; Hewett et al., 2010). Moreover, related to these components of ACL injury are four neuromuscular imbalances (Hewett et al., 2010), namely; 1) an increased reliance on frontal plane control compared to sagittal plane control (dynamic valgus or ligament dominance) (Ford et al., 2003; Hewett et al., 2005), 2) a quadriceps dominant strategy to stabilize the knee joint with lower contributions from the hamstring muscles (quadriceps dominance) (Myer et al., 2007), 3) greater strength, coordination, and balance in the dominant limb (leg dominance) (Hewett et al., 2005), and 4) decreased proprioception and stability of the trunk (trunk dominance) (Hewett and Myer, 2011). Though research is scarce, the relationship between neuromuscular risk factors and knee injuries has also been described in young male athletes (Read et al., 2016a).
Traditionally, kinematics have been assessed by 3-dimensional (3-D) motion capture during different sport-specific movements. The most commonly measured actions are unilateral and bilateral drop jumps (Hewett et al., 2016) and changes of direction (Almonroeder, Garcia and Kurt, 2015). Assessment of kinematic variables using 3-D motion capture, such as knee valgus during jump-landing tasks, provides both valid and reliable indicators of ACL injury risk (Hewett et al., 2005). However, 3-D motion capture is expensive and requires extensive training and expertise; therefore, it is not practical for use in most clinical settings (Krosshaug et al., 2016). Recent research has focused on the development of clinical tools that provide more cost-effective and user-friendly methods of lower extremity biomechanical screening compared to laboratory methods (Crossley et al., 2011; Fox et al., 2016; McCunn et al., 2016; Padua et al., 2011). The most common tools are the single-leg squat (Crossley et al., 2011; Stensrud et al., 2011), single-leg (Stensrud et al., 2011) and bilateral (Ekegren et al., 2009; Hewett et al., 2005; Myer et al., 2007; Padua et al., 2011) drop vertical jump, and continuous tuck jumps (Myer et al., 2008b). The single leg squat is a functional task that does not mimic high intensity, sport-specific actions characteristic of knee injury mechanisms. Whereas, the single-leg and two-leg vertical drop jump only assess the landing phase of a single loading task, which may limit assessment of repeated jump scenarios to identify multiple characteristics of sport-specific deficits. Conversely, the tuck jump assessment (TJA) (Herrington et al., 2013; Myer et al., 2008b; Stroube et al., 2013) evaluates landing technique flaws during a maximal repetitive plyometric activity (Myer et al., 2008a) where landing heights are reflective of each individuals jumping ability and therefore forces are equivalent to those regularly experienced during sporting actions. Furthermore, the repeated nature of the tuck jump assessment provides an indication of reactive strength capabilities and some inherent perturbation, more accurately reflecting the movement demands and high risk mechanics involved in competition (Read et al., 2016b).
The TJA consists of continuous maximal height tuck jumps for ten seconds and involves the analysis of ten quantitative and dichotomous items. These ten items are used to assess the four aforementioned neuromuscular imbalances related to ACL injury (ligament, quadriceps, leg, and trunk dominance) (Hewett et al., 2010). Moreover, this test also includes the assessment of fatigue (Borotikar et al., 2008) and diminished feed-forward, or anticipatory, response (Riemann and Lephart, 2002) as neuromuscular imbalances that may exacerbate lower extremity pathomechanics during a high impact activity (Figure 1).
Participants are scored with a '0' if they meet the specified criteria and with a ' 1 ' if they do not meet the specific criteria. While the TJA is clinically useful (Myer et al., 2008b; Herrington et al., 2013), there are limitations associated with the traditional scoring scheme. The TJA includes non-specific information concerning training and background of the scoring criteria for raters, especially for those raters unfamiliar with the assessment. In addition, the current dichotomous scoring system does not allow the rater to evaluate the severity of dysfunction within items. This limitation makes it difficult to detect both reductions in high-risk movement patterns resulting from neuromuscular training and increases in high-risk movement patterns as a result of fatigue, injury or growth disturbances. Intuitively, by changing the scoring system from the original scale (0-1) to a modified scale (0-2) it may be possible to provide more objective information about an individual's risk of ACL injury. To test this hypothesis, it is necessary to first establish the reliability of this modified scoring scheme. Therefore, the main objective of this study was to evaluate the inter- and intrarater reliability of the TJA with modified scoring.
Twenty-four elite youth volleyball athletes (12 males and 12 females) were recruited from a high performance center in Spain and were included in this study. Study participants were excluded if they presented with any injury (overuse or acute) at the time of testing. Table 1 provides subject characteristics. All of the subjects were actively participating in a four-year professional development program at the time of the study. In addition to a weekend game, subjects had 8-10 training session per week, which each lasted approximately 120 min. Written informed assent and consent were obtained from study participants and their parents. The Sport Council Ethics Committee approved the study.
A week before data collection, study participants were familiarized with the testing procedures and anthropometric measurements were taken. Study participants were shown a video presentation and a live demonstration of correct tuck jump technique. The video consisted of representative images from frontal and sagittal views of a tuck jump. The TJA consists of continuous maximal height tuck jumps for ten seconds. Participants were instructed to place their feet in the middle of the rectangle marked on the floor. This square consisted of four smaller rectangles (Figure 2). In addition, basic instructions given...