Diaphragmatic fatigue is counterbalanced during exhaustive long-term exercise

Based on externally paced (repetitive) short-term trials exercise-induced diaphragmatic fatigue has been shown to manifest after rather than during exercise. The current study aimed at investigating diaphragmatic contractility and diaphragmatic fatigue during self-paced long-term exhaustive exercise at maximally tolerated loading by the use of supramaximal twitch transdiaphragmatic pressure (TwPdi). Seven trained subjects (VO(2max) 63.3+/-13.9 ml kg(-1) min(-1)) performed self-paced long-term exhaustive exercise at maximally tolerated loading (45 min+endspurt, initial workload 85% VO(2max)) followed by recovery (9 min). TwPdi (every 45 s) and ergospirometric data (continuously) were assessed throughout the protocol. Diaphragmatic contractility tended to initially increase during the exercise protocol with a slight decline and final increase during endspurt. Diaphragmatic fatigue manifested only after exercise termination (TwPdi rest 2.6+/-0.8 kPa; TwPdi exercise start/mid/end 2.9+/-0.7 kPa vs. 2.6+/-0.8 kPa vs. 2.4+/-0.6 kPa; TwPdi endspurt/recovery 2.7+/-0.8 kPa vs. 1.9+/-0.6 kPa). In conclusion, diaphragmatic contractility tends to decrease but manifestation of diaphragmatic fatigue is counterbalanced during self-paced long-term exhaustive exercise at maximally tolerated loading.