Feedback Control of Oxygen Uptake During Treadmill Exercise

Abstract

Regulation of exercise intensity is important for aerobic training and for exercise testing. Automatic control of oxygen uptake therefore has potential for use in exercise prescription and in tests to establish markers of cardiopulmonary status. The aim of this study was to investigate the feasibility of automatic feedback control of oxygen uptake during submaximal treadmill exercise. Six healthy male subjects aged 36.0 plusmn 12.2 years (mean plusmn standard deviation) ran on a computer-controlled treadmill while oxygen uptake was measured in real time using a breath-by-breath cardiopulmonary monitoring system. Linear dynamic models of oxygen-uptake response to changes in treadmill speed were obtained empirically using least squares optimization, and the models subjected to a cross-validation procedure. This resulted in selection of a first-order model with a time constant of 47 s. This model was used to design linear feedback controllers with a range of closed-loop bandwidth specifications. When implemented, each controller continuously monitored oxygen uptake and adjusted the commanded treadmill speed in real time in order to track a prespecified oxygen uptake profile. A series of closed-loop control tests illustrate that a single, fixed-parameter controller designed using a dynamic model from just one subject is robust enough to provide satisfactory control of a desired oxygen uptake profile for all subjects tested. Our results confirm the feasibility and robustness of automatic feedback control of oxygen uptake during treadmill exercise. Feedback regulation of exercise intensity via oxygen uptake may contribute to prescription of optimal training and testing programmes.