An optimization algorithm for joint mechanics estimate using inertial measurement unit data during a squat task

The use of dynamic optimization as a tool to estimate joint kinematics and kinetics, and ground reaction forces using data from a single inertial measurement unit (IMU) positioned on the lower trunk was investigated. The feasibility of this approach and its accuracy was explored for the analysis of a squat task, focusing on the ankle, knee and hip joints. An optimal motor control strategy aimed at minimizing the sum of the intersegmental couples and of their time derivatives was imposed to estimate the mechanics of a three-segment sagittal model. Moreover, in the optimization process constraints to the measured vertical acceleration, to the maximal vertical IMU excursion, and with regard to the maintenance of dynamic balance were imposed. Experiments were performed using 10 volunteers. Data were collected from the IMU, from a stereophotogrammetric system (SS) and from a force platform for validation purposes. Results showed a very good consistency of the model output with the lower limb joint trajectories, as obtained using the SS, and with the measured vertical component of the ground reaction (low root mean square differences (<;10%) and high correlation coefficients (0.98)).