Figure 1. Threshold-based footfall detection method.

(A) Principle for foot on (top, red) and foot off (bottom, cyan) detection based on a threshold in resultant speed for foot on and a threshold in distance travelled for foot off. (B) Detailed illustration of the foot-off detection approach: hoof height is extracted during stance; foot off then corresponds to the first frame at which the horizontal distance travelled by the marker exceeds the marker height in stance. (C) Kinematic (dashed lines) and kinetic (solid lines) event detection for foot on (red) and foot off (cyan) illustrated for a single stride of a forelimb during trot on a circle. Top row: resultant speed shown at two magnifications; middle row: distance measurements of horizontal distance travelled relative to the marker hoof height position during stance (left) as well as vertical displacement (right); bottom row: vertical ground reaction force shown at two magnifications. Arrows are shown in those data fields that are used to determine kinematic events. Grey: raw data (unfiltered) for resultant speed. Vertical displacement is given as a reference. Vertical blue dotted line: approximate end of stance. Horizontal green dashed line: 75 N force threshold.