Influence of endurance exercise on respiratory muscle performance

Purpose: During high-intensity, exhaustive, constant-load exercise above 85 % of maximal oxygen consumption, the diaphragm of healthy subjects can fati gue. Although a decrease in trans-diaphragmatic pressure is the most object ive measure of diaphragmatic fatigue, possible extra-diaphragmatic muscle f atigue would not be detected by this method. The aim of the present study w as to investigate the impact of exhaustive, constant-load cycling exercise at different intensities on global respiratory performance determined by th e time to exhaustion while breathing against a constant resistance. Methods : Ten healthy, male subjects performed an exhaustive cycling endurance test at 65, 75, 85, and 95% of peak oxygen consumption ((V) over dot O-2peak) B efore cycling (t(0)) as well as at 10 min (t(10)) and 45 min (t(45)) after cycling, respiratory performance was determined. Results: Breathing enduran ce was equivalently reduced after exhaustive cycling at either 65% (8.4 +/- 4.1 min [t(0)] vs 3.9 +/- 2.8 min [t(10)]), 75% (9.9 +/- 6.1 vs 4.4 +/- 2. 8 min), 85% (9.3 +/- 6.0 vs 3.8 +/- 2.9 min), or 95% (V) over dot O-2peak ( 8.5 +/- 5.1 vs 4.0 +/- 2.5 min) and, therefore, was independent of exercise intensity. Conclusion: This result contradicts previous findings, possibly due to the fact that extra-diaphragmatic muscles are tested in addition to the diaphragm during resistive breathing.