Clinicians frequently assess asymmetry in strength, flexibility, and performance characteristics as a method of screening for potential musculoskeletal injury. The identification of asymmetry in countermovement jumps may be an ideal method to reveal asymmetry in other lower extremity characteristics such as strength that otherwise may require additional testing, potentially reducing the time and burden on both the athlete and clinicians. The present study aims to examine the ability of asymmetry in both the single-leg and two-leg countermovement jump tests to accurately detect hip abduction, hip adduction, and eccentric hamstring strength asymmetry. Fifty-eight young male elite soccer players from the same professional academy performed a full battery of functional performance tests which included an assessment of hip adductor and abductor strength profiles, eccentric hamstring strength profiles, and neuromuscular performance and asymmetries during countermovement jumps. Bilateral variables attained from both the single-leg and two-leg countermovement jump tests included concentric impulse (Ns), eccentric mean force (N), and concentric mean force (N) computed by the VALD ForceDecks software. Average maximal force (N) was calculated bilaterally for the strength assessments. Asymmetry was calculated for each variable using 100 × |(right leg − left leg)/(right leg)| and grouped into three categories: 0 to <10%, 10% to <20%, and 20% or greater. Analyses were performed for the two higher asymmetry groups. The accuracy to detect strength asymmetry was assessed as the sensitivity, specificity, and predictive values for positive and negative tests. The outcomes from the accuracy assessments suggest that the single-leg countermovement jump concentric impulse variable at the 20% threshold is indicative of a youth male soccer player having hip adduction strength asymmetry while also demonstrating more accuracy and applicability than the two-leg countermovement jump concentric impulse variable.

The vertical jump (VJ) is one of the most important movements for basketball athletes and therefore determining modifiable predictors of the VJ would aid substantially in crafting more effective training regimens. The purpose of this study was to determine if isokinetic quadriceps strength and torque predict VJ height and which characteristics and testing speed is the strongest predictor of VJ height. Fifteen subjects (age: 18.5 ± 1.0 years, height: 195.9 ± 6.9 cm, weight: 96.2 ± 13.7 kg) from a single Division I men’s basketball team were recruited for this study. All participants performed a standing vertical jump with arm-swing to assess their maximum VJ height. Participants also completed an isokinetic knee extension strength protocol that included testing at multiple speeds. Pearson and Spearman tests found no significant correlation between jump height and peak torque at any of the speeds. Regression analysis showed a statistically significant relationship between time to peak torque at 300°/s and VJ height (R² = 0.23, p = 0.04). These findings suggest that in a population of elite basketball players, the knee’s ability to rapidly generate torque likely plays a greater role in VJ performance than its ability to generate high magnitude of torque. This presents a potential benefit of explosive training regimens such as plyometrics for maximization of jump performance.

An assessment of protocol reliability is an essential step prior to human subject testing for injury prevention. The purpose of this study was to examine the inter-rater and intra-rater reliability of a portable cervical range of motion and isometric strength protocol designed for special forces combat soldiers who are at risk for cervical spine pain and injury due to exposure to head-supported mass. Eight individuals were tested three times to assess reliability, the standard error of the measurement (SEM), and the minimal detectable change across six range of motion measures and six strength measures of the cervical spine. One tester tested all participants twice for intra-rater reliability, and a second tester assessed the participants to examine inter-tester reliability. All reliability measures demonstrated good to excellent reliability (ICC = 0.70–0.96 (isometric strength); ICC = 0.85–0.94 (range of motion)). All SEM scores were 12% or lower for all reliability measures. The findings of this study demonstrate that the protocol developed for a longitudinal multi-site study is reliable and appropriate to implement for injury prevention in military personnel.