Yi Zhang, Azzam Haddad, Steven W. Su, Branko G. Celler, and Hung T. Nguyen
Heart rate response, Oxygen uptake, Modeling
This paper investigated human heart rate (HR) and oxygen uptake (VO2) dynamics to running exercise and developed an electronic circuitry based mathematical model to quantitatively depict the metabolic and energy-generating process at both onset and offset of exercises. In order to investigate transient responses of both HR and VO2, eight healthy male subjects were asked to run on a motor-controlled treadmill exercise under a predefined running protocol. Heart rate and oxygen consumption were monitored and recorded using a COSMED portable gas analyzer (K4b2, Cosmed). The observed experimental results verified the belief that cardio-respiratory responses dynamics at onset and offset of moderate or high intense exercises are significantly different. In order to find a rational explanation for this phenomenon, a novel idea was inspired by applying a simple switchable resistance-capacitor (RC) circuit to unify the complex dynamics at onset and offset of exercises. The proposed physical system can not only analytically explain body's energy-generating process, metabolism and cardio-respiratory responses, but also mathematically account for cardio-respiratory dynamics at both onset and offset of exercises, in which the continuity of the output and states during switching is guaranteed.
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