The ExtRA Capacity Test: Reliability, validity and normative data of a new clinical tool for assessing shoulder muscle performance

Objectives Introduce The ExtRA Capacity Test, a measure for assessing shoulder muscle performance. Assess its reliability, validity and present normative scores in a large sample of asymptomatic adults. Design Cross-sectional observational study with test–retest Setting Community Participants Volunteers ( n =344, age 20 to 90 years). Interventions The ExtRA Capacity Test involves two capacity tests completed to a 30 beats per minute metronome: maximal scapular plane lateral raises to 90° abduction with 2.5kg of external load, and maximal external rotations in unsupported prone lying with the shoulder at 90° abduction. Reliability was assessed in 30 asymptomatic participants, tested by two raters over two sessions, one week apart, using Bland–Altman analysis to determine mean bias and 95% limits of agreement (LoA) as measures of error. Criterion validity was evaluated in 20 participants using Pearson correlation to examine the relationship between ExtRA and isokinetic dynamometry measures. A normative dataset was also established from 344 asymptomatic individuals across a range of ages, physical activity levels, and both sexes. Results The intra-rater and inter-rater agreement for the ExtRA Capacity Test was assessed in a sample of 30 participants. The 95% LoA for abduction and external rotation measurements ranged from 2.9 to 13.1 repetitions. In a sample of 20 participants, the abduction test showed good/moderate correlation with muscle strength measures but not with the external rotation test. Older age, female sex and not achieving the WHO activity guidelines have a negative impact on ExtRA performance. Conclusions Within the caveats discussed in this paper, ExtRA can be considered a reasonably reliable tool for assessing shoulder strength and control in a clinical setting. The normative database will help clinicians set rehabilitation or return-to-play targets based on sex, age, and physical activity level. Contributions of Paper •This study introduces the ExtRA Capacity Test as a reliable tool for assessing shoulder muscle performance in both sporting and non-sporting populations. •The test demonstrates clinically acceptable intra- and inter-rater reliability, with the abduction component showing a strong correlation with strength measures from Isokinetic Dynamometry. •The normative database established in this study facilitates the evaluation of shoulder performance relative to reference values stratified by age, sex, and physical activity level. •Given its high reliability, the ExtRA Capacity Test can be used to monitor performance changes over time, providing valuable insights for clinical practice and rehabilitation planning.