3D measurement of lower body posture during jumping using inertial sensor

This paper presents a method to estimate a three-dimensional (3D) trajectory and posture of lower limb during jumping motion as well as standing motion using wireless inertial measurement unit (WIMU). Five WIMUs acquire 3D acceleration and 3D angular velocity of five location of lower body (thigh and shank of both leg and back of the waist). Longitudinal direction of lower extremity and trunk is estimated from posture of WIMU which is updated by integration of angular velocity and posture of lower limbs is constructed by connecting joints of each segment. Pressure-sensitive conductive rubber located under heel is used to identify the position of foot on the ground or in the air. When the foot touches on the ground, posture and position of body are calculated in sequence from the foot to the other one via trunk. When both feet are apart from the ground, position of trunk is estimated by double integration of body acceleration. One subject performed vertical jump and estimated posture is compared with the actual one obtained using optical motion capture system. Experimental results show that the estimated posture qualitatively corresponds to the actual one and estimation error of vertical displacement is about 1 [%].