Single-leg squat postural sway reliability: How many trials to analyze for chronic low back pain?

When examining postural sway measures of single-leg squat (SLS), there is a lack of consensus on how many trials are required to obtain reliable and clinically relevant data. Forty adults with chronic low back pain performed five consecutive trials of SLS for each side on a portable force plate. The left and right sides were categorized into problem and non-problem sides by Clinical Pilates assessment. SLS performance was characterized by terminal knee flexion angle, squat duration, peak vertical force and postural sway parameters. Data across five trials were first examined with repeated measures analysis of variance; variables with significant differences were further analyzed using intraclass correlation coefficients (ICC). Using all trials as a reference, the reliability of other trial combinations was assessed to examine the potential effects of learning (2-5 squats, 3-5 squats, 4-5 squats), fatigue (1-2 squats, 1-3 squats, 1-4 squats) and steady-state (2-4 squats). For the non-problem side, postural sway measures were highly reliable (ICC >= 0.9) regardless of the number of trials analyzed. For the problem side, analyzing the 1-4 squats combination offered consistently reliable results across all postural measures (ICC >= 0.72). Thus, it is recommended to analyze the first four consecutive trials to obtain reliable postural sway measures.