Rheological modelling of cardiorespiratory kinetics during sub-maximal exercise

Summary Rheological modelling of cardiorespiratory kinetics during submaximal exercise. With a view to quantify the kinetic evolution of cardiorespiratory variables during a physical exercise the concept of the viscoelastic behaviour of materials is extended to the physiological context. The method is investigated by executing a curve fitting of the observations of five groups of young adult males performing each a 60 minutes submaximal ergometry at constant intensity levels equal to 10%, 25%, 40%, 50% and 75% of their maximal work load Wmax, respectively. The rheological model consists of a fast exponential adjustment, followed by a slow linear regulation and is in accordance with the physiological concept of the non-existence of an ergometric steady state. The linear relationship between the logarithm of the rheological parameters and the work intensity allows a relatively accurate prediction of the time course of the physiological variables during sub-maximal work. Choosing a reference physiological variable (eg, heart rate) at a specific work load level (eg, 25% of Wmax) the dynamic evolution of any of the cardiorespiratory variables at any sub-maximal work load can be estimated. The ratio of the retardation time to the relaxation time of the rheological Burgers model is proposed as a quantitative index to measure the dissipated power when a subject performs a prolonged effort of constant intensity.