This study aimed to describe and compare the ventilation behavior during an incremental test utilizing three mathematical models and to compare the feature of ventilation curve fitted by the best mathematical model between aerobically trained (TR) and untrained (UT) men. Thirty five subjects underwent a treadmill test with 1 km·h^-1 increases every minute until exhaustion. Ventilation averages of 20 seconds were plotted against time and fitted by: bi-segmental regression model (_2SRM); three-segmental regression model (3SRM); and growth exponential model (GEM). Residual sum of squares (RSS) and mean square error (MSE) were calculated for each model. The correlations between peak VO₂ (VO_2PEAK), peak speed (Speed_PEAK), ventilatory threshold identified by the best model (VT_2SRM) and the first derivative calculated for workloads below (moderate intensity) and above (heavy intensity) VT_2SRM were calculated. The RSS and MSE for GEM were significantly higher (p < 0.01) than for _2SRM and 3SRM in pooled data and in UT, but no significant difference was observed among the mathematical models in TR. In the pooled data, the first derivative of moderate intensities showed significant negative correlations with VT_2SRM (r = -0.58; p < 0.01) and Speed_PEAK (r = -0.46; p < 0.05) while the first derivative of heavy intensities showed significant negative correlation with VT_2SRM (r = -0. 43; p < 0.05). In UT group the first derivative of moderate intensities showed significant negative correlations with VT_2SRM (r = -0.65; p < 0.05) and Speed_PEAK (r = -0.61; p < 0.05), while the first derivative of heavy intensities showed significant negative correlation with VT_2SRM (r= -0.73; p< 0.01), Speed_PEAK (r = -0.73; p < 0.01) and VO_2PEAK (r = -0.61; p < 0.05) in TR group. The ventilation behavior during incremental treadmill test tends to show only one threshold. UT subjects showed a slower ventilation increase during moderate intensities while TR subjects showed a slower ventilation increase during heavy intensities.