0808 To better define the dose-response relationship between exercise training and performance, it is necessary to accurately quantify exercise intensity such as oxygen uptake (VO2) during exercise. Conventionally, the monitoring of heart rate (HR) is used to estimate VO2 during exercise. However, since kinetics of VO2 and HR to workload is different, dynamic estimation (DE) of VO2 during exercise is important. PURPOSE: To construct a DE model with use of expired gas data obtained during an incremental run test and to estimate kinetics of VO2 and carbon dioxide output (VCO2) during twelve-minute run test by the system dynamics method. METHODS: Five healthy males took part in this study. All subjects performed an incremental run test by a treadmill in laboratory for the purpose of developing individualized velocity-VO2, −VCO2 equations. Then, the subjects undertook sub maximal 12-minute run test at free intensities in the field. In this modeling, it was assumed that 1) the kinetics of VO2 is function of workload, 2) VCO2 is the sum of metabolic VCO2 that stems from increased VO2 and VCO2 that is generated for buffering blood lactate. Fitness of the DE model was examined by determination coefficient (R2) of estimated and measured VO2 and VCO2. Robustness of simulation to the change in workload was examined by a correlation coefficient (r) between estimation error and change of velocity (acceleration). The data of the incremental run test were used for modeling, and data of 12-minute run test for criteria of validity. RESULTS: The distance covered in 12- minute run test was 2750+/−153 m, mean velocity and coefficient variance of velocity was 230+/−15 m/min, 7.0+/−3.0 %. In all subjects, the goodness of fit index of the estimated VO2 and VCO2 to measured data for the incremental run test was high (R2 >0.97, P < .05), so that the DE model was verified. For estimation of 12-minute run test, estimated VO2 and VCO2 were significantly fitted to the measurements (R2>0.97, P<.05). In a correlational analysis between estimation error and acceleration, there were found not significant correlations (r <0.18, P>.05), thereby indicating robustness of the DE model. CONCLUSIONS: The estimation of dynamics of VO2 and VCO2 using the system dynamics was valid and robust to change of velocity.change of velocity.