Fig. 3

Footprint analysis tools and step parameters. a Complete footprint pattern. A heat map represents pixel intensity and the horizontal line represents the body path. a' Individual feet are labeled with different colors: the left fore, left hind, right fore, and right hind legs are represented in yellow, blue, orange, and green, respectively. b Stance phase dynamics. Each row shows successive frames for a single stance phase. All four legs are represented, top to bottom: left fore (LF), left hind (LH), right fore (RF), and right hind (RH). Stance initiation is to the left and each frame is 4 ms apart. White bar, 1 cm scale. c Individual full stance footprint. Each footprint is individually represented by a pixel intensity heat map. A pixel to centimeter conversion allows the user to measure changes in toe spreading for each footprint (red arrows). d–g Step parameters as a function of speed. Graphical fits are included. x-axis error bars represent standard deviations of the average speed. d Step length increases with speed. e Swing and stance phase durations are inversely proportional to speed. f Duty factor decreases with speed. Linear regression line (y = −0.0027x – 0.6425) determines that for speeds faster then 52.8 cm/s (vertical dashed red line), the duty factor falls below 0.5 (horizontal dashed red line), which confines the transition from a walk to a run-like gait. g Swing speed increases linearly with speed