Gait event detection on level ground and incline walking using a rate gyroscope

Abstract

Gyroscopes have been proposed as sensors for ambulatory gait analysis and functional electrical stimulation systems. Accurate determination of the Initial Contact of the foot with the floor (IC) and the final contact or Foot Off (FO) on different terrains is important. This paper describes the evaluation of a gyroscope placed on the shank for determination of IC and FO in subjects walking outdoors on level ground, and up and down an incline. Performance was compared with a reference pressure measurement system. The mean difference between the gyroscope and the reference was less than -25 ms for IC and less than 75 ms for FO for all terrains. Detection success was over 98%. These results provide preliminary evidence supporting the use of the gyroscope for gait event detection on inclines as well as level walking.

Keywords: Foot Off; Initial Contact; gait event detection; gyroscope.

Figure 1.

The effect of filtering using different cut off frequencies on the gyroscope signal from an unimpaired subject walking on level ground.

Figure 2.

The effect of different cut off frequencies on the detection of IC. The data corresponds to an unimpaired subject walking on level ground.

Figure 3.

Flowchart of the algorithm used for detection of Initial Contact (IC) and Foot Off (FO) from the gyroscope signal. The graph corresponds to data collected from one subject who participated in the study. g(n) is the value of the gyroscope signal at the sample n; AZ: ascending zero crossing; DZ: descending zero crossing; and wt: waiting time. The numbers in the graph relate to steps of the algorithm: (1) detection of ascending zero crossing; (2) detection of signal exceeding threshold of 0.2 V; (3) detection of descending zero crossing; (4) IC detection; (5) waiting time; and (6) FO detection. After FO detection, the algorithm starts again.

Figure 4.

Gyroscope (a, b and c) and Contact Area loaded (d, e and f) signals from Subject 1. Vertical lines in the gyroscope graphs indicate the characteristic features of the gyroscope signal used for the detection of IC and FO events. (a) and (d) are the gyroscope and contact area loaded signals for the subject walking on level ground; (b) and (e) correspond to walking down the incline; and (c) and (f) correspond to walking up the incline.

Figure 5.

Frequency distribution of the time differences between the gyroscope and the reference method for IC and FO event detection for: level ground walking LGW (a) and (b); walking down the incline ID (c) and (d); and walking up the incline IU (e) and (f). The number of events considered were 273 IC and 266 FO for LGW, 36 IC and 36 FO for ID, and 63 IC and 63 FO for IU. Positive differences indicate that the gyroscope method detected the event earlier than the reference.