The purpose of this investigation was to determine the accuracy of the Ground Interaction algorithm, which is used to classify when the foot is on and off the ground. 23 recreationally active subjects volunteered to perform 11 activities on a dual force plate system while wearing insoles containing Inertial Measurement Units (IMUs) from Plantiga Technologies. These IMUs had a sampling frequency of 416 Hz. Insole data was analyzed to determine the off/on-ground location of each foot and find exact takeoff and landing times. The data were separated into 4 groups of activities based on their similarities (single-leg jumps, double-leg jumps, walking/running, in-place activities). Data analysis showed the following results: 1) For single-leg jumps, results showed median errors of -2ms (IQR: 16ms) and -6ms (IQR: 18ms) for takeoffs and landings, respectively (N=309). 2) For double-leg jumps, results showed median errors of 2ms (IQR:22ms) and -2ms (IQR: 16ms) for takeoffs and landings, respectively (N=383). 3) For walking and running, results showed median errors of -4ms (IQR: 18ms) and 2ms (IQR:14ms) for toe-offs and heel strikes, respectively (N=1628). 4) For in-place activities, results showed median errors of -6ms (IQR: 32ms) and 12ms (IQR: 32ms) for takeoffs and landings, respectively (N=212).
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