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 (V˙O2 max 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% V˙O2 max) 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.