Feedback Control System In VO2-kinetics To Predict Energy Expenditure During Intermittent Exercise

Abstract

BACKGROUND Physical activity (PA) has important benefits in maintaining good health. Conventionally, PA or energy expenditure during exercise can be assessed with a monitoring heart rate (HR method) to predict oxygen uptake (VO2). Since kinetics of VO2 and HR are different particularly during intermittent exercise, it is better to predict VO2 based on nonlinear kinetics of VO2. PURPOSE To develop a dynamic prediction (DP) model and to determine accuracy of the DP model by comparing it with measured VO2 in moderate and heavy intermittent exercise. METHODS Five healthy males took part in this study. All subjects performed an incremental test using a cycle ergometer for the purpose of developing individualized HR-VO2 and workload-VO2 equations. To determine two time constants (tau1 and tau2) of VO2 for each subject, they undertook a constant load test at about 85%VO2max. Next, they completed intermittent load tests with two levels of intensity (60% and 80%VO2max) for 30 min. The DP model was developed on feedback control system that is composed of two time constants and workload-VO2 equations. Predicted values (VO2) by the DP model and the HR method were compared with measurements obtained via a metabolic measurement system. RESULTS The DP model showed significantly high determination coefficient to measured VO2 (60%VO2max level: R2 = .97; 80%VO2max level: R2 = .98) in comparison with the HR method (60%VO2max level: R2 = .86; 80%VO2max level: R2 = .89). For both intermittent tests, mean square errors (MSE) in the DP model (1.1 and 4.7, for 60% and 80%VO2max level, respectively) were significantly smaller than those of the HR method (5.7 and 11.8, for 60% and 80%VO2max level, respectively) (P < .05). Thereby, accuracy of the DP model was demonstrated. However, minute-by-minute analysis revealed that there were significant prediction errors in the DP model at recovery period of 80%VO2max intermittent test. These results suggest that time constant of VO2 kinetics was slowed down by excess post-exercise oxygen uptake. CONCLUSIONS The DP model is useful for predicting VO2 during moderate intermittent exercise.