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Putative protective effect of inspiratory threshold loading against exercise-induced supraspinal diaphragm fatigue

¹Laboratoire des Adaptations Physiologiques aux Activités Physiques, Unite Propre de Recherche de l'Enseignement Superieur Équipe d'Accueil (UPRES EA) 3813, Faculté des Sciences du Sport, Poitiers; ²Laboratoire de Physiopathologie Respiratoire, Service de Pneumologie, Groupe Hospitalier Pitié-Salpêtrière, and UPRES EA 2397, Université Paris VI Pierre et Marie Curie, Paris; and ³Service d'Explorations Fonctionnelles, Physiologie Respiratoire et de l'Exercice, Centre Hospitalier Universitaire de Poitiers, Poitiers, France

Submitted 18 May 2004 ; accepted in final form 29 September 2004

The present investigation was intended to assess the consequences of an inspiratory load on the diaphragm central component of fatigue during exercise. We recorded the motor potential evoked (MEP) by transcranial magnetic stimulation of the motor cortex in 10 subjects. The diaphragm and rectus femoris were studied before and 10, 20, and 40 min after two 16-min cycling exercise (E) trials requiring 55% of maximal oxygen uptake: 1) one with an inspiratory threshold load (E + ITL), corresponding to 10% of maximal inspiratory pressure; and 2) the other without the load (E). Dyspnea, heart rate, electromyographic activity of the sternocleidomastoid, and diaphragm work were significantly higher in E + ITL than in E. Neither trial affected the response to phrenic magnetic stimulation, which was performed 15 and 25 min postexercise, or the maximal inspiratory pressure (116 and 120 cmH₂O before E and E + ITL, respectively, and 110 and 114 cmH₂O at 30 min postexercise). Whereas the amplitude of the diaphragm MEP was unaffected by E + ITL (+2.1 ± 29.4%), a significant decrease was observed 10 min after E compared with baseline (–37.1 ± 22.3%) and compared with E + ITL. The MEP amplitude of rectus femoris remained unchanged with E and E + ITL. The recruitment of synergistic agonists during E + ITL may have normalized the major ventilatory stress and reset up the excitability of the diaphragm pathway.

respiratory muscles; transcranial magnetic stimulation; motor cortex

This article has been cited by other articles:

				W. Wang, T. Similowski, and F. Series Respiratory: Interaction between genioglossus and diaphragm responses to transcranial magnetic stimulation in awake humans Exp Physiol, July 1, 2007; 92(4): 739 - 747. [Abstract] [Full Text] [PDF]

				E. Z. Ross, A. V. Nowicky, and A. K. McConnell Influence of acute inspiratory loading upon diaphragm motor-evoked potentials in healthy humans J Appl Physiol, May 1, 2007; 102(5): 1883 - 1890. [Abstract] [Full Text] [PDF]