The interrater and intrarater reliability of the flexibility and strength tests included in the Sport Science Lab® screening protocol amongst professional rugby players

Abstract

Background: Considering the injury incidence rate (IR) associated with elite-level rugby, measures to reduce players’ injury risk are important. Establishing scientifically sound, pre-season musculoskeletal screening protocols forms part of injury prevention strategies.

Objective: To determine the interrater and intrarater reliability of the flexibility and strength tests included in the Sport Science Lab^® (SSL) screening protocol.

Methods: We determine the interrater and intrarater reliability of 11 flexibility and nine strength tests. Twenty-four injury-free, elite, adult (> 18 years), male rugby players were screened by two raters on two occasions. To establish intrarater and interrater reliability, Gwet’s AC₁, AC₂ and intraclass correlation coefficients (ICC) were used for the analysis of binary, ordinal and continuous variables, respectively. Statistical significance was set at 95%.

Results: Flexibility tests which require lineal measurement had at least substantial interrater (ICC = 0.70–0.96) and intrarater reliability (ICC = 0.89–0.97). Most of the flexibility tests with binary outcomes attained almost perfect interrater and intrarater reliability (Gwet’s AC₁ = 0.8–0.97). All strength tests attained at least substantial interrater (Gwet’s AC₂ = 0.73–0.96) and intrarater (Gwet’s AC₂ = 0.67–0.97) reliability.

Conclusion: The level of interrater and intrarater reliability of most of the flexibility and strength tests investigated supports their use to quantify various aspects of neuromusculoskeletal qualities and possible intrinsic risk factors amongst elite rugby players.

Clinical implications: Establishing the reliability of tests, is one step to support the inclusion thereof in official screening protocols. Results of our study, verify the reliability of the simple, clinically friendly strength and flexibility tests included and therefore support their use as preparticipation screening tools for rugby players. Further investigation as to the association thereof to athletes’ injury risk and performance is warranted.