New physiological insights into exercise-induced diaphragmatic fatigue

Abstract Data on the dynamic process and time-point of manifestation of exercise-induced diaphragmatic fatigue (DF) are lacking. Therefore, this study was aimed assessing dynamic changes of diaphragmatic strength during exercise and determining the time-point of DF manifestation. Fourteen trained subjects (maximal oxygen uptake ( V ˙ O 2 max ) 59.3 ± 5.5 ml/min/kg) performed standardized exercise protocols (maximal workload: 85% V ˙ O 2 max ) followed by recovery (6 min). Ergospirometric data and twitch transdiaphragmatic pressure (TwPdi) were consecutively assessed. DF was induced (TwPdi-rest: 2.34 ± 0.26 versus TwPdi-end-recovery 2.01 ± 0.21 kPa, p < 0.01). TwPdi progressively increased during exercise (TwPdi-rest: 2.34 ± 0.26 versus TwPdi-maximal-workload: 3.28 ± 0.38 kPa, p < 0.001). DF was detectable immediately after exercise-termination (TwPdi-maximal-workload: 3.28 ± 0.38 versus TwPdi-early-recovery 2.55 ± 0.34 kPa, p < 0.001). TwPdi during exercise was highly correlated to workload, V ˙ O 2 max and dyspnea ( r = 0.96/ r = 0.92/ r = 0.97; all p < 0.0001). In conclusion, diaphragmatic strength progressively increases with increasing workload, and DF manifests after – rather than during – exercise. In addition, TwPdi is highly correlated to key-measures of ergospirometry, approving the physiological thesis that muscle strength is progressively enhanced and escapes fatiguing failure during high-intensity exercise performance.