Test–retest reliability and variability of knee adduction moment peak, impulse and loading rate during walking

Background: Previous studies have reported good test-retest reliability for peak knee adduction moment (KAM) during walking. However, reliability of other KAM measurements has not been established. Research question: What is the test-retest reliability of peak KAM, KAM impulse, and KAM loading rate measurements during walking in knee-healthy individuals? Methods: Data from 32 knee-healthy participants were analysed in this test-retest reliability study. Various KAM measurements were reported for two sessions with kinematic and kinetic data obtained from a motion capture system synchronised with force plates, with a median of 1 week between sessions. Results: For all KAM measures, intra-class correlation coefficients were above 0.90 and their lower bound 95 % confidence limits exceeded 0.81. However, absolute measurement variability differed across measures, with normalized SEM (8 %–15 %), normalized MDC₉₅ (20 %–40 %), intra-session MAD (10 %–18 %), and inter-session MAD (12 %–22 %) varying over a 2-fold range. Overall and first peak KAM, KAM impulse over 50 % stance, and KAM loading rate (15 frame window) showed ≤10 % and ≤15 % intra- and inter-session MAD, respectively. Significance: This study provided previously undefined test-retest reliability estimates for various KAM measures during walking. Researchers and clinicians should not assume that the various aspects of the KAM curve share similar reliability.