Single-subject analysis reveals variation in knee mechanics during step landing.

PURPOSE Evidence concerning the alteration of knee function during landing suffers from a lack of consensus. This uncertainty can be attributed to methodological flaws, particularly in relation to the statistical analysis of variable human movement data. The aim of this study was to compare single-subject and group analyses in detecting changes in knee stiffness and coordination during step landing that occur independent of an experimental intervention. METHODS A group of healthy men (N=12) stepped-down from a knee-high platform for 60 consecutive trials, each trial separated by a 1-minute rest. The magnitude and within-participant variability of sagittal stiffness and coordination of the landing knee were evaluated with both group and single-subject analyses. RESULTS The group analysis detected significant changes in knee coordination. However, the single-subject analyses detected changes in all dependent variables, which included increases in variability with task repetition. Between-individual variation was also present in the timing, size and direction of alterations. CONCLUSION The results have important implications for the interpretation of existing information regarding the adaptation of knee mechanics to interventions such as fatigue, footwear or landing height. It is proposed that a participant's natural variation in knee mechanics should be analysed prior to an intervention in future experiments.