Basic walker-assisted gait characteristics derived from forces and moments exerted on the walker's handles: results on normal subjects.

This paper describes a method that passively assesses basic walker-assisted gait characteristics using only force-moment measurements from the walker's handles. The passively derived gait characteristics of 22 subjects were validated against motion capture gait analysis. The force-moment based heel initial contact detection algorithm have produced a high level of concordance with heel initial contacts detected by a human inspecting the heel marker data sets of the Vicon video capture system. The algorithm has demonstrated 97% sensitivity and 98% specificity with a narrow 95% confidence interval of +/-1% during all experiments, which included five navigational scenarios. Temporal error in detecting the instances of heel initial contacts were within 5.27+/-3.66% of the overall stride time obtained from Vicon when the subjects walked in a straight line, whereas the toe-off instance estimates were within 5.18+/-2.75% of the gait cycle. The errors in determining the duration of stride time, single support, and double support were within 5.86+/-2.49%, 5.24+/-2.29%, and 4.34+/-2.13% of the gait cycle respectively. The stride time estimated, using the method presented here, correlated well with stride time computations based on visual inspection of Vicon's data, Pearson correlation coefficient r=0.86 for straight line segments. However, absolute errors were too high to estimate the single and double support phases with acceptable accuracy. The potential application of the instrumented walker and the method presented here is longitudinal basic gait assessment that can be performed outside of the conventional gait labs.