Exercising until exhaustion: dynamic integration of brain, muscle and cardio-respiratory functions

Abstract

Endurance performance involves both psychological and physiological processes, but it is far from clear how they interact during exercise. As endurance depends on the interaction between vast number of system’s components distributed at many levels, it is impossible to systematically deduce the macroscopic action behaviour from biochemical microscopic processes. Thus, our aim is to study endurance at macroscopic action level through the variables that best capture the dynamic of interactions between micro and meso-components: the order parameters or collective variables. A set of experiments have been designed to explore psychomotor (elbow angle and pedalling frequency), psychological (attention focus and perceived exertion); and physiological collective variables while cycling, running and weightlifting until exhaustion. A similar macroscopic nonlinear dynamics has been observed during these different types of exercise performed by different populations. The nonlinear effects correspond to those found in other studies that deal, for example, with gene expression cell dynamics which may generate and modify the phenotypic properties of athletes. They include bi-multistability, metastability, criticality and interaction dominant dynamics, as well as noise-induced transitions. With accumulated effort the system reduces the number of degrees of freedom and loses its initial flexibility on all studied levels, leading finally to task disengagement. The general ‘loss of stability’ mechanism is produced by a shift in the coordination between the basic biological processes of excitation and inhibition toward larger time scales. A redefinition of endurance and exhaustion is proposed on the basis of the nonlinear dynamic approach to psychobiological integration, and some practical applications for training interventions and training monitoring are suggested. It is likely that the application of nonlinear dynamics and sta