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The anaerobic threshold (AT) during dynamic physical exercise is a good parameter to quantify oxygen uptake and transport which reflects the functional cardiorespiratory reserve in men. The increasing use of computerized ergospirometric systems has allowed recording, processing and plotting ventilatory variables, cycle by cycle, on a real time basis. So, response changes in carbon dioxide production (VCO2) may be used as a non-invasive measurement of AT. In the present study a custom software was developed to apply bi-segmental models (linear-linear and linear-quadratic) using the least square method for fitting VCO2 data. The lowest value of the residual sum of squares found in VCO2 graphic plots corresponded to AT, expressed as oxygen uptake. Data analysis showed that, despite the good correlation documented between the linear-linear model and the classical visual method, the mathematical method underestimates the AT values when compared to the visual one.