This study examined the effect of exercise-induced muscle damage (EIMD) on ventilatory and perceived exertion responses to cycle exercise. Ten healthy, physically active men cycled for 6 min at moderate intensity and to exhaustion at severe intensity before and 48 h after eccentric exercise (100 squats with a load corresponding to 70% of body mass). Changes in ventilation and ratings of perceived exertion (RPE) were calculated for each individual and expressed against time (moderate and severe exercise) and as a percentage of time to exhaustion (severe exercise). Ventilation increased during moderate exercise at 48 h V(E); 34.5 +/- 5.0 to 36.3 +/- 3.8 l min(-1), P < 0.05) but increases in RPE were not significant. During severe exercise at 48 h, time to exhaustion (TTE) was reduced and V(E) (87.1 +/- 14.1 to 93.8 +/- 11.7 l min(-1)) and RPE (15.5 +/- 1.3 to 16.1 +/- 1.4) were elevated (P < 0.05). When expressed as a percentage of TTE, the differences in ventilation and RPE values disappeared. Findings indicate that the augmented ventilatory response to cycle exercise following EIMD may be an important cue in informing effort perception during high-intensity exercise but not during moderate-intensity exercise.