This study examined the placebo effect of hyperoxic gas inhaled after exercise on respiratory rate and heart rate variability(HRV) and determined the possible psychological contribution of the hyperoxic gas inhalation. Eight healthy male subjects participated in two experimental sessions on two different days; one day using the placebo gas, the other day a control session. Each day the subjects pedaled on a bicycle ergometer at 65% VO_2max for 10 minutes, and after the exercise, took a 20-minute rest where the respiratory curve and electrocardiogram were measured. A spectral analysis analyzed the heart rate variability and the autonomic nervous activity. A questionnaire was used to determine subjects' feelings of effectiveness of the gas inhalation. The high frequency component of the HRV power spectral density in the session with the placebo was 16.5% higher than that without the placebo during the 5 minutes after the exercise, but this was not statistically significant. There was no statistically significant difference in heart rate and the respiratory rate between the two conditions. The questionnaire results indicated no significant correlation between the positive image of a refreshing effect of the hyperoxic gas with the respiratory rate, or with the autonomic nervous activity. These findings suggest that there would be no positive psychological effect on restoration from fatigue with the hyperoxic gas inhaled after exercise.
