For studying the effects of different chemoreceptive drives on the ventilatory responses to muscular work, experiments were carried out with 16 healthy men. They accomplished a 5-min exercise while breathing with different gas mixtures or after hyperventilation. As was shown, the rapid component of the exercise hyperpnea increased with intensifying the hypercapnic and/or hypoxic stimuli and was reduced or abolished with attenuation of these stimuli. At this, hypoxic drive exerted primary influence on the response kinetics. In the steady-state exercise effects of the chemoreceptive stimuli were modulated by biomechanical factors, which leads to a energetically optimum breathing pattern being formed.