Estimation of Tri-Axial Walking Ground Reaction Forces of Left and Right Foot from Total Forces in Real-Life Environments

Continuous monitoring of natural human gait in real-life environments is essential in many applications including disease monitoring, rehabilitation, and professional sports. Wearable inertial measurement units are successfully used to measure body kinematics in real-life environments and to estimate total walking ground reaction forces [Formula: see text] using equations of motion. However, for inverse dynamics and clinical gait analysis, the [Formula: see text] of each foot is required separately. Using an experimental dataset of 1243 tri-axial separate-foot [Formula: see text] time histories measured by the authors across eight years, this study proposes the ‘Twin Polynomial Method’ (TPM) to estimate the tri-axial left and right foot [Formula: see text] signals from the total [Formula: see text] signals. For each gait cycle, TPM fits polynomials of degree five, eight, and nine to the known single-support part of the left and right foot vertical, anterior-posterior, and medial-lateral [Formula: see text] signals, respectively, to extrapolate the unknown double-support parts of the corresponding [Formula: see text] signals. Validation of the proposed method both with force plate measurements (gold standard) in the laboratory, and in real-life environment showed a peak-to-peak normalized root mean square error of less than 2.5%, 6.5% and 7.5% for the estimated [Formula: see text] signals in the vertical, anterior-posterior and medial-lateral directions, respectively. These values show considerable improvement compared with the currently available [Formula: see text] decomposition methods in the literature.