Independence of exercise-induced diaphragmatic fatigue from ventilatory demands

Exercise-induced diaphragmatic fatigue (DF) manifests after - rather than during - exercise. This suggests that DF reflects post-exercise diaphragm-shielding. This study tested the physiological hypothesis that diaphragmatic force-generation undergoes similar regulations during either whole-body-exercise or controlled hyperventilation, but differs during recovery. Ten trained subjects (VO2(max) 60.3+/-6.4 ml/kg/min) performed: I, cycling exercise (maximal workload: 85% VO2(max)); II, controlled hyperventilation (exercise breathing pattern) followed by recovery. Ergospirometric data and twitch transdiaphragmatic pressure (TwPdi) were consecutively assessed. DF occurred following exercise, while hyperventilation enhanced diaphragmatic force-generation (TwPdi-rest 2.28+/-0.58 vs. 2.52+/-0.54, TwPdi-end-recovery: 1.94+/-0.32 kPa vs. 2.81+/-0.49 kPa, both p<0.05). TwPdi was comparable between the two protocols until recovery (p>0.05, RM-ANOVA) whereby it underwent a progressive increase. In conclusion, TwPdi progressively increases and is subject to similar regulations during exercise versus controlled hyperventilation, but differs markedly during recovery. Here, DF occurred after exercise while TwPdi increased subsequent to hyperventilation. Therefore, ventilatory demands regulate diaphragmatic force-generation during exercise, whereas DF must be attributed to non-ventilatory controlled feedback mechanisms.