Our AMTI BP400600 force plates are embedded in the center of the runway (AMTI, Watertown, MA), and each records 3 forces and 3 moments in the vertical, side-to-side, and fore-aft directions and sends them to amplifiers (AMTI MSA-6). An excitation voltage of 10V DC is used, and the gain is set at 4000 unless otherwise noted. Recording frequency is 10 times the video frame rate (1500Hz). The signals are then A-D converted (MDAS DA BNC breakout boxes 2110 and 2115, National Instruments, Austin, Tx) and sampled in ProAnalyst within a voltage range of +/- 10V. They are displayed in channels 1 – 25, with channel zero being reserved for the trigger signal (a 5V square wave). Forces are synchronized and can be displayed synchronous with the video data. The plates are labeled A, B, C, and D. Their arrangement within the runway is as illustrated.

For most experiments, within ProAnalyst, force and moment channels from plate A are in green, from plate B in blue, from plate C in yellow, and from plate D in magenta. Force data from the four plates are in au2 format and can be opened in Excel or text readers. Two time line columns display sample points and time in seconds, with zero being the trigger signal. Coordinate data exported from Xcitex have the same time line. Force data can threfore be synchronized with video data as the data files match temporally, and there are 10 force sampling points per video image.