Definition Inverse dynamics Forces forward Motion Torques inverse Definition Motivations Short version: A process of deriving the kinetics from the Understand and quantify the forces produced by kinematics of the motion muscles, ligaments, and bones via noninvasive Long version: instruments A process by which forces and moments of force are Animate realistic human locomotion indirectly determined from the kinematics and inertial properties of moving bodies Motion and force measurement Motion analysis Interaction of muscle Need to record accurate kinematic properties of the contractions across several motion joints is extremely complex video or infrared based motion analysis systems Most invasive devices can only measure forces in single tissues Need to measure the external forces precisely surgical stables force platforms that measures the ground reaction forces buckle force transducers Motion analysis Joint kinetics Equal in joint forces and moments, but completely Inverse dynamics can only measure the net effect of different in muscle activities the internal forces and torques across several joints Inverse dynamics can compute total load on a system, but can not determine the distribution of the load Inverse dynamics assumes there is no co- contraction of agonist and antagonist muscles Model reduction Model reduction Reduce complex anatomical structures force from bone-on-bone Fankle triceps surae forces F∗ F∗ ligament force from Mankle F F force tibialis anterior MF ground ground contact force contact force −F∗ gravity gravity ∗ ∗ Foot with Forces F and − F Couple F and ∗ muscle added at ankle !−F replaced by force F center moment MF Equation of motion Limitations ID relies on assumption that are not always valid Given body kinematics and anthropometric joint friction and air friction parameters, derive the kinetics quantities using the Newton-Euler equations: non-uniform distribution of mass Newton (linear): movement of joint center of rotation Euler (angular): approximation of body segment parameters Measurement error and numerical error propagation.