New physiological insights into exercise-induced diaphragmatic fatigue

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-O2max) 59.3 +/- 5.5 ml/min/kg) performed standardized exercise protocols (maximal workload: 85% V-O2 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 < 0.0 1). 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-O2 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. (C) 2007 Elsevier B.V. All rights reserved.