Effect of step duration during incremental exercise on breathing pattern and mouth occlusion pressure

We compared the effects of two step durations on breathing pattern, mouth occlusion pressure and ''effective'' impedance of the respiratory system during incremental exercise. Nine normal subjects (mean age: 27.8+/-1.21 years) performed two incremental exercise tests in randomized order: one test with step increments every 1 min 30 s and the other, every 4 min. After a warm-up at 25 W for the 1 min 30 s test, the power was increased by 50 W from 50 W to exhaustion. During the last minute at each power, we measured ventilation ((V) over dot E), tidal volume (VT), breathing frequency (fR), inspiratory and expiratory time (TI and TE), total time of the respiratory cycle (TTOT), TI/TTOT, mean inspiratory flow (VI/TI), mouth occlusion pressure (P-0.1), ''effective'' impedance of the respiratory system (P-0.1(VT/TI)) and venous blood lactate concentration ([La]). Our result showed that at maximal exercise the power was significantly higher (p < 0.01) and [La] lower (p < 0.01) in the 1 min 30 s test. At 100, 150 and 200 W, the 4 min test showed significantly higher oxygen uptake ((V) over dot O-2), carbon dioxide output ((V) over dot CO2), (V) over dot E, P-0.1 fR, VT/TI and HR (p<0.001) and significantly lower TI, TE and TTOT (p <0.01). [La] was significantly higher at 150 W (p<0.05) and 200 W (p < 0.001). At the same (V) over dot CO2, P-0.1 was not significantly different between the two tests, whereas (V) over dot E showed a tendency to be higher (p = 0.08) and P-0.1/(VT/TI) was significantly lower during the 4 min test. In conclusion, this study allowed us to quantify the difference in inspiratory neuromuscular output and ventilatory response between 1 min 30 s and 4 min tests and showed that different step durations alter the relationship between inspiratory neuromuscular output and mean inspiratory flow.