Post-exercise diaphragm shielding: a novel approach to exercise-induced diaphragmatic fatigue.
Based on the "post-exercise diaphragm shielding" hypothesis this study tested whether both diaphragmatic force-generation (DFG) and diaphragmatic fatigue (DF) remain unchanged during consecutive exercise-trials. Twelve subjects (V(O2 max) 58.4+/-6.6 ml kg(-1) min(-1)) performed three consecutive exercise-trials (T(alpha)/T(beta)/T(gamma); workload(max) 85% V(O2 max)) each followed by recovery (6 min). Twitch transdiaphragmatic pressure during supramaximal magnetic phrenic nerve stimulation (TwPdi, every 30s), ratings of perceived exertion (RPE, every 90 s) and ergospirometric data (continuously) were assessed throughout the entire protocol (46.5 min). DFG and DF did not differ among all trials (TwPdi-baseline: 2.2+/-0.7 kPa; TwPdi-peak: T(alpha)/T(beta)/T(gamma) 3.1+/-0.7 kPa vs 3.0+/-0.8 kPa vs 3.2+/-0.8 kPa; TwPdi-bottom: T(alpha)/T(beta)/T(gamma) 1.9+/-0.6 kPa vs 2.0+/-0.7 kPa vs 1.8+/-0.5 kPa, both p>0.4, RM-ANOVA). Furthermore, TwPdi revealed close relationships with RPE (r=0.91, p<0.0001) and oxygen uptake (r=0.94, p<0.0001) during exercise. In conclusion, both DFG (baseline-to-peak) and DF (baseline-to-bottom) achieve similar magnitudes during and after consecutive exercise-trials and are closely linked to RPE and oxygen uptake. This suggests that DF neither reflects impaired diaphragmatic function nor impairs exercise performance; rather it is likely to reflect post-exercise diaphragm shielding.