title: 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 (VO2(max)) 59.3+/-5.5 ml/min/kg) performed standardized exercise protocols (maximal workload: 85% VO2(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, VO2(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.
authors.affiliation: Department of Pneumology, University Hospital Freiburg, Killianstrasse 5, D-79106 Freiburg, Germany. hans-joachim.kabitz@uniklinik-freiburg.de
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Kabitz
authors.forename: David
authors.initials: D
authors.lastname: Walker
authors.forename: Anja
authors.initials: A
authors.lastname: Schwoerer
authors.forename: Florian
authors.initials: F
authors.lastname: Sonntag
authors.forename: Stephan
authors.initials: S
authors.lastname: Walterspacher
authors.forename: Kai
authors.initials: K
authors.lastname: Roecker
authors.forename: Wolfram
authors.initials: W
authors.lastname: Windisch
mesh_terms: D000328:Adult; D015992:Body Mass Index; D003964:Diaphragm / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005541:Forced Expiratory Volume; D006801:Humans; D008168:Lung / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology*; D011312:Pressure; D012129:Respiratory Function Tests; D012132:Respiratory Muscles / Q000502:physiology*; D014797:Vital Capacity