[Purpose] It is unclear whether diaphragmatic breathing (DB) results in lower respiratory muscle oxygen consumption during dynamic exercise. The purpose of this study was to compare oxygen consumption in the respiratory muscles (VOrm) with thoracic breathing (TB) and with DB, in healthy males during hyperventilation. [Subjects and Methods] Ten healthy men participated in this study. The subjects sat on a chair with the backrest reclined at an angle of 60 degrees. Respiratory parameters were measured breath by breath, using an expired gas analyzer. Oxygen consumption was measured for three minutes during quiet breathing. Measurements during TB and DB were performed for one minute each, after connecting a rebreather loading device. The breathing pattern was analyzed by inductance plethysmography, using transducer bands placed over the chest and abdomen that recorded thoracoabdominal movements. [Results] Both ΔVO/body weight and VOrm decreased significantly with DB when compared to that with TB, during hyperventilation. [Conclusion] DB results in less respiratory muscle oxygen consumption, even during dynamic exercise.