Reliability of foot trajectory measures within and between testing sessions

Background. Impaired control of foot trajectory during the swing phase of gait is hypothesized to increase the risk of slipping or tripping. Before assessing the predictive validity of foot trajectory measures with respect to incidence of falls, it is necessary to establish their reliability. The purpose of this study is to assess within- and between-session reliability of foot trajectory measures and traditional temporal-distance measures in healthy elderly women during gait. Methods. Sixteen healthy, elderly women (ages 65-79 years) completed six sets of five trials each of natural and fast cadence gait during a 3.5-hour period on each of 4 days. An optoelectric motion analysis system and heel switches were used to obtain both foot trajectory (minimum toe clearance during swing, vertical, and horizontal heel contact velocities) and temporal-distance measures (step width, cadence, velocity, stride length, and time). Results. Within-session test-retest reliability of all variables at natural and fast speeds was good to excellent, with intraclass correlation coefficients (ICCs) of greater than 0.9 for all but one measure (fast cadence stride time). ICCs for between-session test-retest reliability were slightly lower, but still greater than 0.9 for all but two measures (fast cadence stride time and natural cadence vertical heel contact velocity). Heel contact velocities quantified at the instant of heel contact correlated strongly with values obtained by averaging over the last 2% of the gait cycle. Discussion. The good to excellent within- and between-session reliability of these foot trajectory measures supports their use as a possible means of assessing subtle changes in gait motor control. Confirmation of an association between alterations in foot trajectory measures and incidence of falls awaits further study.