C h r i s t o p h S z u b s k i , Wo l f g a n g L ö s c h e r u n d M a r t i n B u r t s c h e r
Auswirkungen von Hypoxie auf neuromuskuläre Aktivierung, motorkortikale Erregbarkeit und zentrale Ermüdung The effects of hypoxia on neuromuscular activity, motor cortical excitability and central fatigue
S U M M A RY The effects of acute hypoxia on motor cortex excitability, force production, spinal excitability, central and peripheral fatigue were studied in fourteen healthy male subjects. Electrical stimulations of the right ulnar nerve were performed and transcranial magnetic stimulations (TMS) were delivered to the first dorsal interossoeus (FDI) motor cortex area during acute hypoxic and normoxic condition. The stimulations were given in relaxation, during brief maximum voluntary contraction (MVC) and sustained 90s-MVC. Hypoxia was induced by breathing a fraction of inspired oxygen of 12% via a face mask. M-wave, twitch, F-wave, resting motor threshold, recruitment curves, and intracortical inhibition and intracortical facilitation were measured. Moreover, force, motorevoked potential (MEP), silent period (SP) and voluntary activation were determined during brief and sustained isometric maximal right index finger abduction. Force, M-wave, and F-wave were not influenced by the delivery of oxygen. The resting motor threshold was significantly lower in hypoxia (55,9 ± 9,40 %) compared to normoxia (57,50 ± 10,48 %) (P < 0.01), but recruitment curve, intracortical inhibition and facilitation, and MEP were unaffected by hypoxia. In contrast, SP during brief MVC was significantly shortened in hypoxia (158,21 ± 33,96 ms) compared to normoxia (169,42 ± 39,69 ms) (P < 0,05). No hypoxia-related changes in force, M-wave, MEP, normalized MEP, SP, or voluntary activation were observed during the fatiguing MVC and in the recovery phase. At the end of the hypoxic post-exercise period the twitch force was significantly potentiated by 133 % of the pre-fatigue amplitude (P < 0,05). Furthermore, after the cessation of the hypoxic sustained MVC twitch amplitudes recovered more rapidly compared to normoxic values (P < 0,05). Our data demonstrated that acute hypoxia results in increased motor cortical excitabili-
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