Hi, I am designing control equation for an exoskeleton and for that I have carried out simulation of assistive torque required by the human musculoskeletal system during certain defined load carrying task. To achive this assistive torque profile, I have switched on the Reaction force (Reaction.Type = On) at that joint and arrived at the assistive torque. I am interested to know and study the underlying equation for the reaction forces produced by AnyBody Modeling System during simulation.Kindly share the details in this regard.
Unfortunately, it's not so easy to describe how the reaction forces are estimated in AnyBody in a forum post. Fortunately, you can find several publications that describe how the solver works, in particular this one.
To briefly guide you, the reaction force is an output from the inverse dynamics analysis, where the solver tries to minimize a function of recruited force (so all the muscles and recruited actuators), while satisfying the dynamic equilibrium equations. The reaction forces can be freely used by the solver if it can help in reducing the recruited force. Fundamentally, it is an optimization problem due to the presence of a large number of muscles. So, there are a whole bunch of factors like motion, external load, muscle strength, muscle moment arms, etc, that have to accounted in each time step to determine the optimal solution, including the reaction force needed.