We investigated the effects of age on breathing pattern, mouth occlusion pressure, the ratio of mouth occlusion pressure to mean inspiratory flow, and venous blood lactate kinetics during incremental exercise. Mouth occlusion pressure was used as an index of inspiratory neuromuscular activity, and its ratio to mean inspiratory flow was used as an index of the "effective impedance" of the respiratory system. Nine elderly male subjects [mean (SD) age: 68.1 (4.8) years] and nine young male subjects [mean (SD) age: 23.4 (1.3) years] performed an incremental exercise test on a bicycle ergometer. After a warm-up at 30 W, the power was increased by 30 W every 1.5 min until exhaustion. Our results showed that at maximal exercise, power output, breathing pattern, and respiratory exchange values, with the exception of tidal volume and the "effective impedance" of the respiratory system, were significantly higher in the young subjects. The power output and oxygen consumption values at the anaerobic threshold were also significantly higher in the young men. At the same power output, the elderly subjects showed significantly higher values for minute ventilation, respiratory equivalents for oxygen uptake and carbon dioxide output (CO(2)), mean inspiratory flow, occlusion pressure and lactate concentration than the young subjects. At the same CO(2) below the anaerobic threshold (0.5, 0.75, 1.00 and 1.25 l x min(-1)), minute ventilation and lactate concentration were also significantly higher in the elderly subjects. We observed a significantly higher minute ventilation at CO(2) values of 0.5, 0.75, 1.00 (P < 0.001) and 1.25 l x min(-1) (P < 0.05) in the elderly men, and a significantly higher lactate concentration at CO(2) values of 1.00 (P < 0.05) and 1.25 l x min(-1) (P < 0.01). In conclusion, the ventilatory response in elderly subjects is elevated in comparison with that in young subjects, both below and above the anaerobic threshold. This study demonstrates for the first time that this ventilatory increase, both below and above the threshold, is partly due to an increased lactate concentration.