Force response of locust skeletal muscle

Abstract

The force response of the locust hind leg extensor muscle to input excitation pulses is modelled. Despite the processes behind muscle contraction being well established, no broadly valid method of modelling skeletal muscle exists. Studies that compare the merits of existing models are extremely scarce and researchers make various assumptions in order to simplify the complex, nonlinear behaviour of the muscle. Locusts provide an opportunity to develop a muscle model in a simpler system, that will still show similar properties to that of mammalian muscles. In developing a model previous work is considered, and complexity is introduced in the experimental conditions in stages. This meant a model could be built up in parts. This approach reduces the need for questionably valid assumptions.

The main focus of this work is modelling activated isometric muscle. Experimental data was collected by stimulating the extensor muscle and measuring the force generated at the tibia. In the first instance the response to individual stimulus pulses is modelled. This is extended to develop a predictive model capable of estimating the isometric force response to general pulse train inputs. In developing the model, data was fit to existing models, and from this an improved isometric model developed. The effect of changing the isometric muscle length is considered. Commonly changing the muscle length is assumed to just scale the force response. This assumption is poor. The dynamics of the force response were found to be modified by the change in muscle length, and the isometric model adapted to include this dependency.

Results related to the non-isometric behaviour are also presented. Passive muscle is usually just modelled over the lengthening period, however, the whole stretch-shorten cycle is considered here. A model, adapted from the standard linear model, is developed to describe the passive
force response.

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Identifiers

ORCID for E. Rustighi: orcid.org/0000-0001-9871-7795

ORCID for B.R. Mace: orcid.org/0000-0003-3312-4918

ORCID for Philip L. Newland: orcid.org/0000-0003-4124-8507

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