Background and Objective: Breathing through the nose and mouth is one of the controversial issues during exercise. The present study was scheduled to investigate a quantitative approach to habitual versus the obligatory switching point from nasal to oronasal breathing during exercise as well as coincidence of soft palate movement as the main aims of this study, that has not been studied previously. Materials and Methods: In this experimental study, twenty-five young adult volunteers (12 males and 13 females) participated in the study. An incremental exercise protocol was incorporated in three protocols for determination of switching point from nasal to oronasal breathing during habitual, obligatory conditions, and determination of change in soft palate position. In two latter conditions, subjects were advised to breathe via nasal route as long as they could. Switching point from nasal to oronasal breathing was determined by a CO2 sensor. Results: Duration of habitual nasal breathing was shorter than tolerated nasal breathing. Obligatory opening of mouth and change in soft palate position were coincident. Ventilation increment at habitual shift from nasal to oronasal respiration was lower than obligatory one. Switching time to oronasal breathing correlated either with ventilation increment or exercise workload. Rate of ventilation was higher in females but switching time was significantly longer in males in three mentioned conditions. In the last two protocols, ventilation incrimination was significantly lower in females. Conclusion: In conclusion, duration of tolerated nasal breathing was longer than habitual one and changes in the position of soft palate occurs simultaneously.