The aim of the present study was to determine the development of the inspiratory muscle fatigue in healthy human during incremental cycling to exhaustion under mild and heavy resistive loaded breathing in air and oxygen. Minute ventilation, tidal volume, respiratory rate, inspiratory mouth pressure, and parasternal EMG activities were recorded during an incremental cycling test under mild (12 cmH(2)O x l(-1) x s(-1)) and heavy (40 cmH(2)O x l(-1) x s(-1)) resistive loading in air and oxygen in 8 men. The degree of inspiratory muscle fatigue was evaluated by analysis of the dynamics of inspiratory mouth pressure, 'tension-time' index, and the fall of the high-to-low (H/L) ratio of the parasternal EMG. It was found that oxygen breathing slowed the development of inspiratory muscles fatigue evoked by incremental cycling only during mild resistive loading, whereas hyperoxia had not influence on inspiratory muscle endurance during heavy resistive loading.