AimThe aim of this study was to evaluate the acute effects of different inspiratory resistance devices and intensity of loads via nasal airway on the breathing pattern and activity of respiratory muscles in children with mouth breathing syndrome.MethodsChildren with mouth breathing syndrome (MBS) were randomized into two groups based on inspiratory load intensity (20% and 40% of the Maximal Inspiratory Pressure). These subjects were assessed during quiet breathing, breathing against inspiratory load via nasal airway and recovery. The measurements were repeated using two different devices (pressure threshold (PT) and flow resistance (FR)). Chest wall volumes and respiratory muscle activity were evaluated by optoelectronic plethysmography and surface electromyography, respectively.ResultsDuring the application of inspiratory load, there was a significant reduction in respiratory rate (p<0.04) and an increase in inspiratory time (p<0.02), total time of respiratory cycle (p<0.02), minute volume (p<0.03), tidal volume (p<0.01) and scalene and sternocleidomastoid muscles activity (RMS values, p<0.01) when compared to quiet spontaneous breathing and recovery, regardless of load level or device applied. The application of inspiratory load using the FR device showed an increase in the tidal volume (p<0.02) and end-inspiratory volume (p<0.02).ConclusionFor both devices, the addition of inspiratory loads using a nasal interface had a positive effect on the breathing pattern. However, the FR device was more effective in generating volume and, therefore, has advantages compared to PT.