One male and eleven female subjects were examined in order to compare their ventilatory and heart rate responsiveness to hypoxia at rest and during moderate exercise (60 W) .
1) The slopes of the ventilatory response curve to hypoxia (AVE) were 306.5±229.5 and 1, 082.9±928.3l⋅min^-1⋅mmHg at rest and during exercise, respectively. Significant difference (p<0.05) between the two groups was found.
2) The slopes of the hypoxia-heart rate response curve (A_HR) were 704.9±477.3 and 1, 165.5±587.8 beats⋅min^-1⋅mmHg at rest and during exercise, respectively. The latter was significantly greater than the former (p<0.05) .
3) A significant relationship between AVE and AHR was observed (p<0.05) .
4) The relationship between ΔV_E50 and ΔHR₅₀, the increments of ventilation and heart rate from room-air to end-tidal Po₂ 50 mmHg, was also significant (p<0.01) .
These results indicate that hypoxic ventilatory and heart rate responsiveness during exercise is significantly greater than at rest, and point to the highly synergistic nature of the relationship between respiratory and cardiac regulations.