Reproducibility of gait parameters at different surface inclinations and speeds using an instrumented treadmill system

Instrumented treadmill systems allow the practical assessment of gait parameters under several walking conditions. Aim of this study was to evaluate the reproducibility of gait parameters at different surface inclinations and walking speeds using an instrumented treadmill system in healthy individuals. A total of 20 subjects (10 women) with a mean age of 31 years were evaluated with an instrumented treadmill system (FDM-T, Zebris Medical GmbH) during two identical test sessions. Spatial (step length, step width, foot rotation), temporal (cadence, single-limb support, step time) and ground reaction force (heel force, toe force, time to heel force, time to toe force) gait parameters were assessed at three treadmill inclinations (level, uphill, downhill) and five speeds (2, 3, 4, 5, 6 km/h). Between-day reproducibility was evaluated with smallest detectable changes for agreement and intraclass correlation coefficients for reliability. Low agreement and reliability were observed for (i) step length, cadence and step time during slow (2 and 3 km/h) and uphill walking and (ii) time to heel force and time to toe force under the majority of walking conditions. The instrumented treadmill system used in this study provided reproducible measurements for the majority of the evaluated spatial, temporal and ground reaction force gait parameters in healthy individuals. The assessment of time to heel/toe force should be however avoided, and particular care should be taken for some spatial (step length) and temporal (cadence and step time) parameters while walking uphill and/or at slow speeds.