Modeling of muscle atrophy and exercise induced hypertrophy

Abstract

A better understanding of the time course of changes in muscle performance in response to spaceflight and exercise is required to maintain sufficient muscle function for long duration spaceflight. This paper presents a semi-empirical and dynamic muscle adaptation (atrophy and hypertrophy) model driven by a muscle activation profile that is directly related to muscle exercise intensity and exercise-rest cycles. The effect of muscle adaptation is described by two phenomenological parameters (s; τ), where s is related to the physiological limit of adaption and τ governs rate of adaptation. Both s and τ mathematically depend on the instantaneous muscle activation level (a). The model is calibrated against selected atrophy and hypertrophy experimental data. It was demonstrated that: (1) the model is capable to handle muscle atrophy and hypertrophy in a unified setting; (2) the model can be used for prediction of muscle atrophy during a 6-month spaceflight under two different exercise regimes.