Test-retest and inter-rater reliability of a field-based test battery to assess lower limb isometric strength and inter-limb asymmetry in healthy adult endurance runners of various training levels

Abstract Objectives This study aimed to evaluate the test-retest and inter-rater reliability of lower-limb isometric strength assessments using handheld dynamometry, and to examine the magnitude of inter-limb strength asymmetries in healthy adult endurance runners. Methods In total, 53 recreational runners of various training levels completed field-based tests measuring isometric hip adduction, hip abduction, knee extension, knee flexion, ankle dorsiflexion, and ankle plantar flexion strength across three sessions. Reliability was assessed using the intraclass correlation coefficient (ICC), standard error of measurement (SEM), standard error of prediction and coefficient of variation (CV). Systematic bias was assessed via Wilcoxon signed-rank tests. Results Test-retest reliability of the different tests ranged from moderate to good (ICC = 0.60–0.84), while inter-rater reliability ranged from moderate to excellent (ICC = 0.60–0.91). Variability was relatively low, with CV values ≤ 5.9%. These measures were generally comparable between subgroups. No significant differences were found across test sessions, except for left hip abduction (p = 0.022), right ankle dorsiflexion (p = 0.007) and right ankle plantar flexion (p = 0.019). Inter-rater comparisons showed no significant differences, except for right knee flexion (p = 0.048) and left ankle dorsiflexion (p = 0.006). Inter-limb asymmetry magnitudes ranged from 8.0% to 19.1% across tests. Conclusion Acceptable reliability for assessing group-level isometric lower-limb strength in distance runners was demonstrated. However, given the moderate to good test-retest ICCs and measurement variability, practitioners should exercise caution when using this test battery to monitor individual-level asymmetry magnitudes over time. Trial registration: ClinicalTrials.gov (NCT06808399). Registered on 02 April 2025.