Ground reaction forces were collected using 46.2-cm X 50.8-cm force plates, mounted to each corner inside the treadmill and underneath the treadmill belt support plate. The signal was collected at 1,000 Hz over 30 gait cycles at varying speeds, pressures, and simulated suit weights and then stored for subsequent analysis. The vertical components of each of the four force-plates were resolved into one vertical component and summed together for each of the 30 gait cycles. For all trials, in each of the conditions, the peak vertical force was determined using customized MATLAB computer code over the 30 gait cycles.
Four strain-gauge-type force plates (AMTI, Watertown, Mass.), which were mounted to the frame of the treadmill under the belt, recorded ground reaction force (GRF) during the ambulation trials. The GRFs recorded on the treadmill were normal (perpendicular) to the surface of the treadmill. Two additional force plates (AMTI, Watertown, Mass.) were used during the exploration task trials to record GRF and center of pressure (COP). During exploration tasks, the subjects would stand on top of the force plates while performing their task.
For ambulation data, a state-of-the-art Vicon MX motion-capture system (Vicon, Oxford, England) was used to capture the kinematic data. Custom-made camera mounting frames were made by the ABF to ensure the stability of the cameras during flight, which is critical to collecting accurate data. The camera rack was also modified from a square rack type of mount in phase I, with the cameras spread across the crosspieces, to separated posts that were spread farther apart in phase II. This was done to increase the viewing, or capture volume and increase the number of markers visible at any one time.