PURPOSE : The purpose of this study was to clarify the effects of prolonged expiration (PE) on respiratory and cardiovascular responses and autonomic nervous activity during the exercise.METHODS : Twenty-five healthy men (22±1years) were classified according to the breathing mode during the exercise : 2-second inspiration and 4-second expiration in 1 : 2 group, 3-second inspiration and 3-second expiration in 1 : 1 group and normal breathing in control group. The 6-minute exercise was performed at anaerobic threshold (AT) and 60%AT using a cycle ergometer as an exercise protocol. Respiratory rate (RR) and tidal volume (TV) were measured by the expired gas analysis. The power of low- (LF) and high-frequency components (HF) was analyzed from a Holter electrocardiogram to assess the heart rate variability. RESULTS : RR and LF/HF were significantly lower, TV and HF were significantly higher during the exercise of 60%AT and AT in the 1 : 1 and 1 : 2 groups than in the control group (P<0.05 or P<0.01). The increase of HR was significantly lower and that of HF was significantly higher during the exercise at 60%AT in the 1 : 2 group than in the 1 : 1 group (P<0.05). CONCLUSION : PE activated the parasympathetic nervous activity and consequently restrained an excessive increase of HR during the exercise at 60%AT.