title: Influence of Upper-Body Exercise on the Fatigability of Human Respiratory Muscles.
abstract: Diaphragm and abdominal muscles are susceptible to contractile fatigue in response to high-intensity, whole-body exercise. This study assessed whether the ventilatory and mechanical loads imposed by high-intensity, upper-body exercise would be sufficient to elicit respiratory muscle fatigue.
  
  
  
  Seven healthy men (mean ± SD; age = 24 ± 4 yr, peak O2 uptake [V˙O2peak] = 31.9 ± 5.3 mL·kg·min) performed asynchronous arm-crank exercise to exhaustion at work rates equivalent to 30% (heavy) and 60% (severe) of the difference between gas exchange threshold and V˙O2peak. Contractile fatigue of the diaphragm and abdominal muscles was assessed by measuring pre- to postexercise changes in potentiated transdiaphragmatic and gastric twitch pressures (Pdi,tw and Pga,tw) evoked by supramaximal magnetic stimulation of the cervical and thoracic nerves, respectively.
  
  
  
  Exercise time was 24.5 ± 5.8 min for heavy exercise and 9.8 ± 1.8 min for severe exercise. Ventilation over the final minute of heavy exercise was 73 ± 20 L·min (39% ± 11% maximum voluntary ventilation) and 99 ± 19 L·min (53% ± 11% maximum voluntary ventilation) for severe exercise. Mean Pdi,tw did not differ pre- to postexercise at either intensity (P > 0.05). Immediately (5-15 min) after severe exercise, mean Pga,tw was significantly lower than pre-exercise values (41 ± 13 vs 53 ± 15 cm H2O, P < 0.05), with the difference no longer significant after 25-35 min. Abdominal muscle fatigue (defined as ≥15% reduction in Pga,tw) occurred in 1/7 subjects after heavy exercise and 5/7 subjects after severe exercise.
  
  
  
  High-intensity, upper-body exercise elicits significant abdominal, but not diaphragm, muscle fatigue in healthy men. The increased magnitude and prevalence of fatigue during severe-intensity exercise is likely due to additional (nonrespiratory) loading of the thorax.
authors.affiliation: 1Academy of Sport and Physical Activity, Sheffield Hallam University, Sheffield, UNITED KINGDOM; 2Division of Sport, Health and Exercise Sciences, Brunel University London, London, UNITED KINGDOM; and 3School of Life and Medical Sciences, University of Hertfordshire, Hertfordshire, UNITED KINGDOM.
authors.forename: Nicholas B
authors.initials: NB
authors.lastname: Tiller
authors.forename: Ian G
authors.initials: IG
authors.lastname: Campbell
authors.forename: Lee M
authors.initials: LM
authors.lastname: Romer
mesh_terms: D000009:Abdominal Muscles / Q000502:physiology; D001132:Arm / Q000502:physiology*; D003964:Diaphragm / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008176:Lung Volume Measurements; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D055815:Young Adult