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Publications

Journal Article Ahead of print

PubMed: 41617217 DOI: 10.1152/japplphysiol.00852.2025

The time course of exercise-induced expiratory and inspiratory muscle fatigue.

J Appl Physiol (1985)

Authors: Tim A Hardy, Matt R Chadwick, Carrie Ferguson, Troy J Cross, Bryan J Taylor

Affiliations

  • School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom.
  • Leeds Institute of Rheumatic & Musculoskeletal Medicine, Faculty of Medicine & Health, University of Leeds, Leeds, United Kingdom.
  • Respiratory Research Center, The Lundquist Institute for Biomedical Innovation at Harbor-UCLA Medical Center, 1124 W Carson St. Torrance, CA 90502.
  • Division of Respiratory and Critical Care Physiology and Medicine, Harbor-UCLA Medical Center, 1000 W Carson St. Torrance, CA 90509.
  • Heat and Health Research Centre, The University of Sydney, Sydney, NSW, Australia.
  • Cardiovascular Diseases, Department of Cardiovascular Medicine, Mayo Clinic Florida, Jacksonville, USA.

Abstract

Inspiratory muscle fatigue develops during exercise prior to intolerance. The expiratory muscles are less resistant to fatigue compared to the inspiratory muscles, but the time-course of inspiratory and expiratory muscle fatigue during exercise has not been compared. Ten healthy adults (25 ± 5 years; 2 females) cycled on three separate occasions at 25% of the difference between estimated critical power and peak ramp incremental power (severe-intensity domain) for: 1) 100% of time to the limit of tolerance (T LIM; 10.2 ± 2.6 min); 2) 75% T LIM (7.7 ± 1.9 min); and 3) 50% T LIM (5.1 ± 1.3 min). Expiratory and inspiratory muscle fatigue were quantified as the pre- to post-exercise reduction in the gastric (Pga tw) and diaphragm (Pdi tw) twitch pressure response to magnetic stimulation of the thoracic and cervical nerves, respectively. Pga tw and Pdi tw were reduced from baseline values after 50% T LIM (11.9 ± 8.2% and 9.5 ± 9.2%, both P < 0.05). The magnitude of expiratory and inspiratory muscle fatigue increased progressively at 75% T LIM (20.0 ± 12.6% and 15.2 ± 10.1%, both P < 0.05) and 100% T LIM (30.3 ± 15.6% and 22.4 ± 12.5%, both P < 0.05), but there was no difference between muscle groups (P > 0.05). Expiratory and inspiratory muscle fatigue develops relatively early during severe intensity exercise and increases progressively in magnitude by exercise intolerance. The onset and progression of respiratory muscle fatigue during exercise is not different between the expiratory and inspiratory muscles.

MeSH

Exercise, Physiology, Muscles, Respiration, Muscle Fatigue, Fatigue, Physical Exertion, Environment