Use of mouthpiece and noseclips after breathing pattern at rest and during moderate exercise. Our purpose was to extend observations on mouthpiece breathing to its effects on the cardiorespiratory response to intense exercise and to develop and validate an algorithm for computer-assisted analysis of breathing pattern recorded with respiratory inductive plethysmography. Six normal men performed incremental bicycle exercise to volitional exhaustion on two occasions with and without mouthpiece and noseclip. ECG and breathing pattern recorded with a respiratory inductive plethysmograph were analyzed manually and with computer assistance. Mouthpiece breathing increased tidal volume and respiratory cycle time by up to 63 and 33% respectively (p < 0.02) during mild exercise, but it did not alter performance, heart rate, or breathing pattern at maximal exercise. Mean differences between inductive plethysmographic and spirometric tidal volumes were < 5% during validation at rest and maximal exercise. Application of the proposed algorithm for semiautomatic breathing pattern analysis provided significant time savings with no loss in precision compared with manual analysis. In conclusion, in normal men, performance and breathing pattern during maximal exercise are not altered by a mouthpiece and noseclip, and accurate computer-assisted measurement of ventilation from external transducers may be performed even during intense exercise.