Reliability of spatiotemporal and kinetic gait parameters determined by a new instrumented treadmill system

Abstract

Background: Despite the emerging use of treadmills integrated with pressure platforms as outcome tools in both clinical and research settings, published evidence regarding the measurement properties of these new systems is limited. This study evaluated the within- and between-day repeatability of spatial, temporal and vertical ground reaction force parameters measured by a treadmill system instrumented with a capacitance-based pressure platform.

Methods: Thirty three healthy adults (mean age, 21.5 ± 2.8 years; height, 168.4 ± 9.9 cm; and mass, 67.8 ± 18.6 kg), walked barefoot on a treadmill system (FDM-THM-S, Zebris Medical GmbH) on three separate occasions. For each testing session, participants set their preferred pace but were blinded to treadmill speed. Spatial (foot rotation, step width, stride and step length), temporal (stride and step times, duration of stance, swing and single and double support) and peak vertical ground reaction force variables were collected over a 30-second capture period, equating to an average of 52 ± 5 steps of steady-state walking. Testing was repeated one week following the initial trial and again, for a third time, 20 minutes later. Repeated measures ANOVAs within a generalized linear modelling framework were used to assess between-session differences in gait parameters. Agreement between gait parameters measured within the same day (session 2 and 3) and between days (session 1 and 2; 1 and 3) were evaluated using the 95% repeatability coefficient.

Results: There were statistically significant differences in the majority (14/16) of temporal, spatial and kinetic gait parameters over the three test sessions (P < .01). The minimum change that could be detected with 95% confidence ranged between 3% and 17% for temporal parameters, 14% and 33% for spatial parameters, and 4% and 20% for kinetic parameters between days. Within-day repeatability was similar to that observed between days. Temporal and kinetic gait parameters were typically more consistent than spatial parameters. The 95% repeatability coefficient for vertical force peaks ranged between ± 53 and ± 63 N.

Conclusions: The limits of agreement in spatial parameters and ground reaction forces for the treadmill system encompass previously reported changes with neuromuscular pathology and footwear interventions. These findings provide clinicians and researchers with an indication of the repeatability and sensitivity of the Zebris treadmill system to detect changes in common spatiotemporal gait parameters and vertical ground reaction forces.

Figures

Figure 1

Instrumented treadmill system. Spatiotemporal gait parameters and ground reaction forces were estimated using an instrumented treadmill system that incorporated a capacitance–based pressure array consisting of 7,168 transducers with a spatial resolution of 0.85 cm.

Figure 2

Illustration of a typical vertical ground reaction force–time trace obtained with the instrumented treadmill. The magnitude and timing of the vertical ground reaction force braking peak (P1), and final propulsive peak (P2) were calculated for comparison across the three test sessions. Time to peak force was expressed as a percentage of the stance phase duration.

Figure 3

Bland and Altman plot for step length of the left leg. Bias (solid line) and RC95% (dashed lines) for step length between sessions 2 and 3 (within–day) (a) and between sessions 1 and 2 (between–day) (b) and between sessions 1 and 3 (between–day) (c). Note that the RC95% is mathematically identical to the Minimum Detectable Change, which represents the minimum change in score (at an individual level) that reflects true change (with 95% confidence), rather than measurement error alone. Negative values reflect an increase in step length.