Author(s): STADNYK, A., WELLS, M., WALKER, J., MCINTOSH, B., MCLEAN, B., Institution: UNIVERSITY OF TECHNOLOGY SYDNEY, Country: AUSTRALIA, Abstract-ID: 1774

INTRODUCTION:
Physical performance testing is central to monitoring neuromuscular status, guiding training prescription, and informing injury risk management in elite team sport athletes. Hamstring injuries are particularly problematic due to time lost and increased likelihood of re-injury. In rugby league, practitioners increasingly favour field based isometric strength assessments due to their feasibility and reduced athlete burden, yet evidence supporting their validity and reliability remains limited. The aims of this study were to establish the criterion validity and interday test–retest reliability of field based test isometric knee flexion tests in elite rugby league athletes.
METHODS:
The validity of a modified VALD NordBord field-based test protocol was assessed against a laboratory-based Biodex 4 Isokinetic Dynamometer. Sample size was determined a priori based on an expected intraclass correlation coefficient (ICC) of 0.85 (lower acceptable limit = 0.60), α = 0.05, and 90% power, resulting in a minimum required sample of 24. Thirty-four elite rugby league athletes (female NRLW and male reserve grade players) completed the validity and/or reliability assessments. Tests were performed at knee joint angles of 30°, 60°, and 90°, and validity was assessed using Pearson correlations and Bland–Altman analyses, while reliability was quantified using ICC(2,1) two-way mixed effects model for absolute agreement of single measurements.
RESULTS:
The field-based isometric knee flexion test values had strong, positive correlations with the lab-based device measurements at 30° (r=0.55, 95% CI [0.21-0.77], t(24), p=0.003), 60° (r=0.69, 95% CI [0.41-0.85], t(24), p< 0.001), and 90° (r=0.54, 95% CI [0.15-0.78], t(20), p=0.010), with systematic biases of +15, +40, and +58 N⋅m, respectively. The 95% limits of agreement in all tests exceeded ±38 N⋅m. Test-retest reliability for knee flexion at 30° and 60° was moderate-to-excellent (ICC ≥ 0.86, p <0.001), with coefficients of variation of 15.0% at 30° and 12.1% at 60°, and standard errors of the mean being 10.6% and 8.6%, respectively. Mean (SD) time between tests was 11 (8.29) days for validation, and 5 (4.35) days for reliability assessment. An insufficient number of participants (n=4) completed reliability assessments at 90° due to team scheduling changes, so analysis was unable to be completed.
CONCLUSION:
These findings indicate that these field-based isometric knee flexion tests provide estimates of neuromuscular strength in elite rugby league athletes that have good agreement with a lab-based criterion device, and good inter-day reliability as determined by ICC. However, practitioners should be mindful of the joint angle-specific systematic bias and wide limits of agreement present within these tests, which may be relevant to muscle length role in hamstring strain injuries. These findings highlight a need for practitioners to consider the appropriateness of these tests within the context of the athlete preparation outcomes of interest.