In clinical applications, the quantitative analysis of gait variability using kinematic and kinetic characterizations can be helpful to medical doctors in monitoring patient recovery status. A high-speed camera system and a stationary force plate can only accurately measure complete ground reaction force (GRF) and body orientations during a few steps, but data on successive gait measurements including three-dimensional (3D) force and motion in different environments is really desired by clinical researchers and doctors. We have developed a mobile force plate and 3D motion analysis system (M3D) by integrating small triaxial force sensors and 3D inertial sensors for estimating multi-axial GRF and orientations of feet during successive gait movements. In order to verify the measurements of the developed system, we used a stationary force plate as a reference measurement system to simultaneously measure the triaxial GRF and center of pressure (CoP) when a subject was required to wear the M3D. Static and dynamic test experiments were implemented to validate the triaxial force measurement of the M3D. Experimental results verify that the developed system can be used to measure the triaxial force with acceptable precision (error: less than 6.4% of maximum measurement force). An application trial was carried out to analyze normal gait and paralysis gait using the M3D. Quantitative differences between gaits were analyzed, based on the results of the vertical component of GRF and medial-lateral directional angular flexions of the feet.
