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Alpha-motoneuron excitability at high altitude

B Kayser¹, R Bökenkamp, T Binzoni

¹Département de Physiologie, Centre Médical Universitaire, Geneva, Switzerland.

European Journal of Applied Physiology and Occupational Physiology

|January 1, 1993

Summary

Chronic hypobaric hypoxia may not inhibit alpha-motoneuron pool function. Studies show the H-reflex gain increased at altitude, suggesting preserved, not inhibited, neuromuscular function in skeletal muscles.

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Area of Science:

Physiology
Neuromuscular Science
Altitude Research

Background:

Chronic hypobaric hypoxia is hypothesized to inhibit alpha-motoneuron pool activity.
This inhibition could limit maximal activation of working skeletal muscles.

Purpose of the Study:

To investigate the effect of chronic hypobaric hypoxia on alpha-motoneuron excitability.
To determine if altitude acclimatization impacts neuromuscular responses in skeletal muscles.

Main Methods:

Six subjects were evaluated at sea level and after acclimatization at 5,050 m.
Recruitment curves for the Hofmann-reflex (H-reflex) and direct muscle response (M-response) of the soleus muscle were measured.
Key parameters including net alpha-motoneuron excitability (Hmax:Mmax ratio), thresholds, gain, and latency times were analyzed.

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Main Results:

Latency times and the Hmax:Mmax ratio remained unchanged at altitude.
Thresholds for both H-reflex and M-response were unaltered.
The gain of the H-response was significantly higher at altitude compared to sea level.

Conclusions:

Chronic hypobaric hypoxia does not appear to inhibit the alpha-motoneuron pool.
The increased H-reflex gain at altitude suggests preserved or enhanced neuromuscular function.
Skeletal muscle activation may not be limited by alpha-motoneuron inhibition under these conditions.