The Effect of Stimulus Timing on Unplanned Gait Termination

Gait termination can be challenging for balance-impaired populations, including lower limb amputees. As powered prosthetic ankle devices come to market, it is important to better understand gait termination timing in an unplanned situation. Timing patterns were examined in unplanned gait termination to determine a threshold for being able to terminate gait in 1 step. Time to terminate gait (TTG) was also examined, using both final heel strike and center of mass (COM) acceleration metrics. Fourteen able-bodied subjects walked over ground and terminated gait in response to a randomly-timed auditory stimulus. A lumbar-mounted accelerometer and footswitches were used to assess timing of gait termination. Subjects were able to terminate gait in 1 step if the stimulus occurred at or before 19.8% of gait cycle. Later stimulus resulted in a 2-step stop pattern. The TTG using COM acceleration was greater than when using heel strike data. Motion of the COM was not fully arrested until 162 ± 38% of gait cycle. The stabilization phase between heel strike and COM motion arrest was greater for 1-step stops (1.41 ± 0.42 s) than 2-step stops (0.96 ± 0.33 s). These findings indicate gait termination timing should be calculated using COM motion, including the stabilization phase post heel strike.