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This Article Full Text Free Full Text (PDF) Free All Versions of this Article: 101/6/1673    most recent 00617.2006v2 00617.2006v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Szubski, C. Articles by Löscher, W. N. Search for Related Content PubMed PubMed Citation Articles by Szubski, C. Articles by Löscher, W. N.

The effects of short-term hypoxia on motor cortex excitability and neuromuscular activation

¹Department of Sports Science, University of Innsbruck; and ²Department of Neurology, Innsbruck Medical University, Innsbruck, Austria

Submitted 2 June 2006 ; accepted in final form 3 August 2006

The effects of acute hypoxia on motor cortex excitability, force production, and voluntary activation were studied using single- and double-pulse transcranial magnetic stimulation techniques in 14 healthy male subjects. Electrical supramaximal stimulations of the right ulnar nerve were performed, and transcranial magnetic stimulations were delivered to the first dorsal interosseus motor cortex area during short-term hypoxic (HX) and normoxic (NX) condition. M waves, voluntary activation, F waves, resting motor threshold (rMT), recruitment curves (100–140% of rMT), and short-interval intracortical inhibition and intracortical facilitation were measured. Moreover, motor-evoked potentials (MEPs) and cortical silent periods were determined during brief isometric maximum right index finger abductions. Hypoxia was induced by breathing a fraction of inspired oxygen of 12% via a face mask. M waves, voluntary activation, and F waves did not differ between NX and HX. The rMT was significantly lower in HX (55.79 ± 9.40%) than in NX (57.50 ± 10.48%) (P < 0.01), whereas MEP recruitment curve, short-interval intracortical inhibition, intracortical facilitation, maximum right index finger abduction, and MEPs were unaffected by HX. In contrast, the cortical silent periods in HX (158.21 ± 33.96 ms) was significantly shortened compared with NX (169.42 ± 39.69 ms) (P < 0.05). These data demonstrate that acute hypoxia results in increased cortical excitability and suggest that acute hypoxia alters motor cortical ion-channel function and GABAergic transmission.

transcranial magnetic stimulation; voluntary activation; cortical silent period