Calculation of stride timing.

(A) Enlarged view of a portion of the walking bout shown in Fig. 5. Although it is not obvious, the x-, y-, and z-positions of the TiTa points (shown in black, red, and blue, respectively) are displayed here as points rather than lines to demonstrate the discretization due to the digital video capture. Discontinuities typically occurred when the forward and backward tracking intersected (see Methods). The gray boxes denote the stance phases of each leg, as defined by the leg's z-coordinate. The dashed, green boxes show how the stance phase calculation changes when the foot's anterior and posterior extreme positions (AEP and PEP, respectively) are used to determine stride timing.