Oxygen Uptake Response to Switching Stairs Exercise by Non-parametric Modeling

Abstract Background: Oxygen uptake plays a vital role in evaluating endurance performance during exercise and is widely used for metabolic assessment. In order to guarantee the accuracy of oxygen uptake estimation, suitable modeling method applied to estimating cardiorespiratory response during interval training exercise should be investigated. Methods: In this study, the oxygen uptake during the exercise phase (i.e. ascending or descending) of the stairs exercise is recorded and the experimental dataset features ten participants and a range of different exercise periods. Based on the designed experiment protocol, a non-parametric modeling method with kernel-based regularization is generally applied to estimate the oxygen uptake changes during the interval stairs exercise that is close to the daily life status. Results: The non-parametric model exhibits the smallest variance and higher accuracy than fixed-order models in both one period and two periods during exercise. Moreover, the fitness of two periods is significantly lower than those of half or one period for the non-parametric model and the IR model is quite different in different periods, which indicates that the model of the system is changing with exercise periods. Conclusions: Compared with the fixed-order models on accuracy, stability and compatibility, the modeling results demonstrate the effectiveness of the non-parametric modeling approach. The influence of exercise duration on estimated fitness reveals that the model of the phase-oxygen uptake system is not time-invariant related to respiratory metabolism regulation and muscle fatigue. Accordingly, it allows us to study the humans’ conversion mechanism at different metabolic rates and facilitates the standardization and development of exercise prescriptions.