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Strength and Fatigue: Experiments and Modeling
Book chapter

Strength and Fatigue: Experiments and Modeling

Laura Frey-Law
Human Motion Simulation: Predictive Dynamics, pp.127-147
Elsevier Inc
2013
DOI: 10.1016/B978-0-12-405190-4.00006-4

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Abstract

Predictive dynamics uses joints as represented by degrees of freedom (DOF) to characterize the kinematics and dynamics of the motion. Each joint must have limits on its strength; indeed, each individual person has a varying degree of strength that must be represented. Strength limits for the virtual human model are needed to simulate a realistic motion using the predictive dynamics approach. Without proper strength limits for various joints, the simulated motion may not be physically possible. This chapter addresses the problem of determination of strength and fatigue limits of the human body. The concept of joint space is described where the strength limits (torque limits) for each DOF of the body joint are determined. Because of the use of joint space, individual muscle activation values are not needed. Determination of the strength data for a joint and its normalization are discussed. The predicted joint torques can be compared with the normative torque limits or 3D strength surfaces, and can be included as constraints in the optimization process. Modeling of dynamic fatigue is a challenging problem. For static fatigue, the well-known curvilinear relationship between fatigue and intensity is the Rhomert’s curve or the intensity-endurance time curve. In this chapter, a dynamic fatigue model is also proposed, which is capable of addressing the effects of work intensity, joint position, contraction velocity, and rest intervals.
 Rhomert’s Curve Dynamic Fatigue Static Fatigue Strength limits Joint Space

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