Abstract
In this paper we present an experimental method of parameterising the passive mechanical characteristics of the bicep and tricep muscles in vivo, by fitting the dynamics of a two muscle arm model incorporating anatomically meaningful and structurally identifiable modified Hill muscle models to measured elbow movements. Measurements of the passive flexion and extension of the elbow joint were obtained using 3D motion capture, from which the elbow angle trajectories were determined and used to obtain the spring constants and damping coefficients in the model through parameter estimation. Four healthy subjects were used in the experiments. Anatomical lengths and moment of inertia values of the subjects were determined by direct measurement and calculation. There was good reproducibility in the measured arm movement between trials, and similar joint angle trajectory characteristics were seen between subjects. Each subject had their own set of fitted parameter values determined and the results showed good agreement between measured and simulated data. The average fitted muscle parallel spring constant across all subjects was 143N/m and the average fitted muscle parallel damping constant was 1.73Ns/m. The passive movement method was proven to be successful, and can be applied to other joints in the human body, where muscles with similar actions are grouped together.
Highlights
In this paper we describe a passive method for parameterising the passive mechanical characteristics of human muscles in vivo
We have previously shown that the classical Hill muscle model is not structurally identifiable and parameter values cannot be uniquely obtained through measurement [20]
The 3 initial sets of seeds used were the reported fitted values in previous work [26]: all zero values; and the physiological realistic seed based on the range listed in Section 5, the latter was arbitrarily selected as barm, bm2 and blim = 0.5 Nms/rad, 0.5 Ns/m and 0.5 Nms/rad respectively, km1 = km2 = 90 N/m, bm1 = 0.3 Nms/rad and klim = 0.2 Nm/rad
Summary
In this paper we describe a passive method for parameterising the passive mechanical characteristics of human muscles in vivo. A study of the movement of the elbow joint and the procedure to obtain parameter values of an arm model incorporating the elbow flexor and extensor muscles as modified Hill muscle models is presented. Hill type muscle models [16], which are widely used in musculo-skeletal modelling, represent the muscle as a combination of mechanical components. Because these mechanical components model properties that result from a large number. The muscles are the flexor muscle, defined as the bicep muscle in this model, which anatomically describes the bicep brachii and brachialis acting in parallel; and the extensor muscle, triceps brachii, defined as the tricep muscles in this model
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