Variability of walking in able-bodied adults across different time intervals

This study aimed to quantify the variability of walking in young adults across measurement sessions held at varied time intervals. Inconsistent marker placement, a major source of variation in gait measurement, was minimized in this study in order to quantify how much variation is attributable to participants naturally altering their walking. Three-dimensional gait data were captured from five young adults on four sessions on each of four days. After Day 1, marker locations were identified with permanent pen to minimise variance due to inconsistent marker placement. A multi-level linear regression model was used to estimate intertrial and inter-session variance for two hour, within-day, across-a-day and across-a-week intervals. Inter-trial variation was relatively constant within sessions and ranged from a standard deviation (SD) of 0.7 degrees to 2.5 degrees. Inter-session variation differed across gait variables and time intervals, with a maximum variation of 2.4 degrees (hip rotation, across a week). Young adults varied their kinematic walking patterns (SD = 1-2 degrees) over intervals of 2 hours to 1 week. In reliability studies, variations of this magnitude may simply reflect natural or `intrinsic? human variation rather than marker placement error.