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Effects of exhaustive incremental treadmill exercise on diaphragm and quadriceps motor potentials evoked by transcranial magnetic stimulation

¹Laboratoire de Physiopathologie Respiratoire et Unité de Réanimation, Service de Pneumologie, Groupe Hospitalier Pitié-Salpêtrière, Assistance Publique-Hôpitaux de Paris, 75013 Paris; ²Service de Physiologie Respiratoire, Centre Hospitalier Universitaire de Rouen, 76031 Rouen; ⁴Unité de Recherche de l'Enseignement Supérieur EA 2397, Université Paris VI Pierre et Marie Curie, 75013 Paris; and ⁵Service de Pneumologie Pédiatrique, Unité Institut National de la Santé et de la Recherche Médicale E 0213, Hôpital Armand Trousseau, Assistance Publique Hôpitaux de Paris, 75571 Paris, France; ³Respiratory Muscle Laboratory, Royal Brompton Hospital, SW3 6NP London; and ⁶Respiratory Muscle Laboratory, King's College Hospital, Guy's, King's and St. Thomas' School of Medicine, SE1 9RT London, United Kingdom

Submitted 2 April 2003 ; accepted in final form 3 September 2003

It is unknown whether changes in corticomotor excitability follow exercise in healthy humans. We hypothesized that a fall in the diaphragm and quadriceps motor-evoked potential (MEP) amplitude elicited by transcranial magnetic stimulation of the motor cortex would occur after an incremental exercise task. In 11 healthy subjects, we measured transdiaphragmatic pressure and isometric quadriceps tension in response to supramaximal peripheral magnetic nerve stimulation. MEPs were recorded from these muscles in response to transcranial magnetic stimulation. After baseline measurements, subjects performed a period of submaximal exercise (gentle walking). Measurements were repeated 5 and 20 min after this. The subjects then exercised on a treadmill with an incremental protocol to exhaustion. Transcranial magnetic stimulation was performed at baseline and at 5, 20, 40, and 60 min after exhaustive exercise, and force measurements were obtained at baseline, 20 min, and 60 min. Mean exercise duration was 18 ± 4 min, and mean maximum heart rate was 172 ± 10 beats/min. Twitch transdiaphragmatic pressure and twitch isometric quadriceps tension were not different from baseline after exercise, but a significant decrease was observed in diaphragm MEP amplitude 5 and 20 min after exercise (60 ± 38 and 45 ± 24%, respectively, of baseline, P = 0.0001). At the same times, the mean quadriceps MEPs were 59 ± 39 and 74 ± 32% of baseline (P < 0.0001 and P < 0.01, respectively). Studies using paired stimuli confirmed a likely intracortical mechanism for this depression. Our data confirm significant depression of both diaphragm and quadriceps MEPs after incremental treadmill exercise.

cortical magnetic stimulation; paired stimuli; motor-evoked potential

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