Test-retest reliability and minimum detectable change for various frontal plane projection angles during dynamic tasks

Abstract Objective Establish between-day test-retest reliability metrics for 2-dimensional frontal plane projection angles (FPPAs) during the lateral step-down (LSD), single-limb squat (SLS), single-limb landing (SLL), and drop vertical jump (DVJ). Design Test-retest reliability study. Setting University laboratory. Participants 20 healthy adults (12 female, age = 23.60 ± 1.93 years old, body mass index = 24.26 ± 2.54 kg/m2) were tested on 2 separate occasions 7–14 days apart. Main outcome measures Intraclass correlation coefficients (ICC), standard errors of the measurement (SEM), and minimal detectable change (MDC) values across the LSD, SLS, SLL, and DVJ for the following body region variables: trunk, trunk on pelvis, pelvis, hip, thigh to vertical, knee, and shank to vertical. Results There was moderate-to-substantial between-day test-retest reliability for nearly all body regions across all tasks (ICC = 0.65–0.96). SEM values varied across body regions and tasks (0.9–3.5°). MDCs were variable (2.3–9.8°). Of the body regions, MDCs were largest for the knee and hip. By task, MDCs were lowest for the LSD. Conclusions This study identified between-day test-retest reliability metrics for 2-dimensional FPPAs across a variety of body regions during commonly assessed clinical tasks. These data allow clinicians and researchers to more confidently assess true change between assessments or over time.