Development Of A High-fidelity Human Muscle Fatigue Model With Physiological Characteristics For Use In The Modeling Of The Elbow Flexor-extensor Motion

To simulate high-fidelity and realistic human motion,it is necessary to develop an accurate biomechanics muscle model that is able to capture fatigue with physiological characteristics.In this dissertation,a fatigue human muscle model is developed and indirectly verified via the human elbow arm flexure-extension modeling and experimentations.The fatigue muscle model is modified from an existing calcium ion transport model by including parameters for PCSA,muscle length,shortening velocity and nerve cell activation.Further,in our muscle model we hypothesize that the popularly accepted 3 types of motor unit(representing slow fatigue,fast fatigue and fatigue resistant) can be amalgamated into one single motor unit that possesses all these 3 characteristics.We termed this new approach as a self-regulating adaptive model.Except for some non-invasive situations,it is generally not viable to perform direct in vivo experiments with human muscles and thus,to verify our work,we develop a fatigue muscle human arm elbow model for checking against laboratory measurements involving human subjects.Among the information obtained are strength curves of the elbow joint torque,the maximal endurance time(MET) under varying external loadings,and fatigue characteristics of the elbow under isometric and isokinetic contractions.Extensive comparisons of the predicted results versus the experimental results are provided.Further,male and female muscle responses from our model and from experiments are compared.The comparisons in our study can be grouped into 4 main and specific categories: (1) the elbow flexure joint torques for both static and dynamic states as a function of the elbow joint angles-we found that the maximal torque angle occurs at about 70°;(2) the MET varies inversely with the percentage maximum voluntary contraction(MVC) -at MVC＜30%,the MET exhibits an exponential drop with MVC and at MVC＞30%, the MET fiats-out to an approximately linear decrease with MVC;(3) the flexor torque is generally larger than extensor torque-the maximal flexor torque at about 1.7 times the maximal extensor torque;and(4) the ratio of the male-female maximal torque is 2 with the female muscle being more fatigue-resistant-the contrast is especially more evident in the lower relative loading range.We showed that in all eases,our theoretical predictions agree reasonably well with the experimental results.We believe our work is very useful for the study of the human musculo-skeletal motions and biomechanies,particularly,in the field of sports and rehabilitation medicine.