Title: Inverse-Inverse Dynamics Simulation of Musculo-Skeletal Systems
Abstract: Introduction Like all mechanical simulation, multibody analysis of the musculo-skeletal system is essentially a matter of determining unknown output, the dependent variables, from assumed input, the independent variables. The choice of input and output causes the simulation to fall into either of two categories known respectively as inverse dynamics and forward dynamics. In inverse dynamics, muscle and joint forces are computed based on given external loading and motion, i.e., the joint and muscle forces are the dependent variables. In forward dynamics, the situation is the opposite. A superficial investigation may indicate that inverse dynamics holds some practical advantages over forward dynamics because the inverse dynamics input (IDI) is easier to record than individual muscle forces (the input of forward dynamics). However, many practical movements also involve IDI that is difficult to measure or changes with the working conditions. In bicycling, for instance, the rider at each instant can choose foot angles and pedal forces independently of crank position, and this choice is likely to change if a working condition, for instance the cadence, is changed. Thus, it may appear that inverse dynamics cannot be applied to cases involving unknown or changing IDI. In forward dynamics, the equivalent problem of unknown muscle forces is solved by formulating an optimum control problem [1], i.e., find the forces that provide the desired motion and fulfil some optimality criterion. The same idea applied to inverse dynamics entails an optimization of the unknown IDI, effectively creating an inverse-inverse algorithm. The two approaches differ only in the choice of variables in the optimization problem, and the best approach to a given problem depends on the expected difficulty of the two optimization problems. In this work, we investigate how the inverseinverse algorithm can be used to handle kinematic indeterminacy as exemplified by bicycling.
Publication Year: 2000
Publication Date: 2000-01-01
Language: en
Type: article
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Cited By Count: 12
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