TY - JOUR T1 - Diaphragm fatigue in self-paced running exercise of different durations JF - European Respiratory Journal JO - Eur Respir J VL - 38 IS - Suppl 55 SP - 4878 AU - Thomas U. Wüthrich AU - Elisabeth C. Eberle AU - Christina M. Spengler Y1 - 2011/09/01 UR - http://erj.ersjournals.com/content/38/Suppl_55/4878.abstract N2 - Introduction: Diaphragm fatigue (DF) was shown to develop during high intensity constant-load exercise (CLE) above 85% of maximal oxygen consumption (VO2max). CLE does, however, not appropriately reflect field trial conditions where exercise intensity is regulated by complex feedforward and feedback mechanisms, possibly aiming to reduce/prevent DF. Therefore, the development of DF was assessed in 11 well-trained athletes (age=31±4 yrs, VO2max=66.7±4.6 mlmin-1kg-1) in 15 and 30min running time trials (TT). We hypothesized that DF would be larger in the 30TT where more time is spent above 85%VO2max.Methods: Before and 4min after completion of the TTs, esophageal and gastric pressures were assessed to calculate transdiaphragmatic twitch pressures (Pdi,tw) during cervical magnetic stimulation.Results: All subjects developed DF (Pdi,tw reduction, ΔPdi,tw ≥10%) in the 15TT and 7/11 subjects in the 30TT. On average, ΔPdi,tw was 23.0±6.5 (15TT) and 18.5±12.1% (30TT; p=0.13). Mean exercise intensities were 89.4±3.5 (15TT) and 86.0±3.7%VO2max (30TT; p=0.07) with similar mean durations above 85%VO2max (11.9±2.0min; range: 7-14min; 15TT) and (16.2±9.7min; 1-28min; 30TT; p=0.19). The individual between-TT difference in ΔPdi,tw did not correlate with the difference in time spent above 85%VO2max (R2=0.20) but correlated with the difference in the average exercise intensity above 85%VO2max (R2=0.49; p=0.02).Conclusion: In TT-conditions, the degree of DF is not related to the duration spent above 85%VO2max but it is related to the exercise intensity when exercising above the 85%VO2max-threshold. ER -