What happens before the first step? A New Approach to Quantifying Gait Initiation Using a Wearable Sensor

Abstract

Background: Walking is a volitional behavior that requires planning and initiation before a step is observed. Following a signal to begin walking, studies of gait initiation in specialized labs have identified three phases that occur during the transition from a standing position via anticipatory postural adjustment (APA) to the first step. Routine instrumented gait testing outside of the laboratory setting focuses on gait execution and does not include gait initiation measures.

Research question: Can a single IMU sensor be used for performing gait initiation evaluations outside the lab?

Methods: We recorded walking in young (N = 41) and older (N = 26) adults using an instrumented gait mat while they were wearing a 3D accelerometer on their lower back. Subjects were instructed to begin walking following an auditory signal. An algorithm was developed to extract the following measures from the acceleration signal: gait initiation time, measured from the start of the auditory cue to begin walking and ends at the heel-strike of the swing leg, time-to-APA (reaction time), APA duration and swing time (execution of the first step).

Results: Intraclass correlation coefficient analysis showed good to excellent agreement between gait initiation metrics obtained with the gait mat and the wearable sensor (mean 0.88, range [0.75-0.96]). Except for swing time, all measures were longer in the older subjects, compared to the young adults (p < 0.01).

Significance: Extracting gait initiation measures from routine instrumented gait testing may facilitate studies that can better determine the extent to which impaired gait planning and execution contribute to mobility impairments.

Keywords: accelerometer; aging; anticipatory postural adjustment; gait; inertial measurement units.

Figure 1:

Example of an acceleration signal during a gait initiation trial and the parameters that are extracted by the algorithm. The first vertical line at time 0 represents the beginning of the trial at which the auditory cue was played. The next 3 vertical lines are the points derived by the algorithm: 1) APA start 2) Initiation leg toe-off, which also marks the end of the APA, and 3) Initiation leg heel-strike, which also represents the end of the gait initiation. The time measured from the auditory cue to these 3 points define the measures Time to APA, Time-to-toe-off and Time-to-Heel-strike and is also depicted in the figure. Two additional measures are derived from the 3 times: the APA duration and the Swing time duration.

Figure 2:

Bland-Altman plots of A: time-to-APA, time-to-APA end, and time-to-heel-strike, B: APA duration and C: swing time duration.

Figure 3:

Correlations examples between gait initiation metrics. Time-to-APA and Time-to-toe-off are not correlated as seen in a. The correlations between APA duration and Time-to-heel-strike and to Time-to-toe-off are depicted in B and C.