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J Appl Physiol (October 15, 2004). doi:10.1152/japplphysiol.00528.2004
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Submitted on May 18, 2004
Accepted on September 29, 2004

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

S. JONVILLE1*, L. JUTAND1, T. SIMILOWSKI2, A. DENJEAN3, and N. DELPECH1

1 Faculte des Sciences du Sport, Laboratoire des Adaptations Physiologiques aux Activites Physiques, UPRES EA 3813, Poitiers, France
2 Groupe Hospitalier Pitie-Salpetriere, Laboratoire de Physiopathologie Respiratoire, Service de Pneumologie & UPRES EA 2397, Paris, France
3 Faculte des Sciences du Sport, Laboratoire des Adaptations Physiologiques aux Activites Physiques, UPRES EA 3813, Poitiers, France; CHU, Service d Explorations Fonctionnelles, Physiologie respiratoire et de l Exercice, Poitiers, France

* To whom correspondence should be addressed. E-mail: sophie.jonville{at}wanadoo.fr.

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 (MEP) evoked by transcranial magnetic stimulation of the motor cortex in ten subjects. The diaphragm and rectus femoris were studied before and 10, 20 and 40 min after two 16-min cycling exercise trials requiring 55% of VO2MAX: i) one with an inspiratory threshold load (E + ITL) corresponding to 10% of maximal inspiratory pressure and ii) 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 minutes post-exercise, or the maximal inspiratory pressure (116 cmH2O and 120 cmH2O before E and E + ITL, respectively, and 110 cmH2O and 114 cmH2O at 30 minutes post-exercise). Whereas the amplitude of the diaphragm MEP was unaffected by E + ITL (+ 2.1 ± 29.4 %), a significant decrease was observed 10 minutes after E as compared to baseline (-37.1 ± 22.3 %) and as compared to 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.




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