Objectives: 

The cardiovascular and respiratory responses during exercise in altitude at a central level are generally well known, but real-time near-infrared spectroscopic (NIRS) measurements can add new knowledge on a peripheral level. Our aim was to more profoundly define the correlation between whole body functional parameters and the changes in the oxygenation profile of a working muscle during exercise, whilst comparing changes at sea level with changes in the conditions of acute hypoxia.

Materials: 

6 healthy human males of 29 (±7) years of age, 177 (±3) cm tall, and 75.5 (±9.5) kg total body weight (TBW).

The subjects underwent a series of 6 minute sub-maximal exercise bouts on a bicycle with 5 minute rests in between, raising the work load by 30 W for each subsequent bout. This was performed at 0 m and at a simulated altitude of 5000 m in a hypobaric chamber which, equates as acute hypoxia.

Results: 

The percent change in the total vascular peripheral resistance (TPR) versus the local oxygen extraction of the vastus lateralis showed similar pattern at sea level and at simulated altitude; increasing local extraction with decreased resistance until reach 45-50% of the TPR. At simulated altitude a comparatively higher extraction was observed for the same work loads as for sea level measurements.

Furthermore, the total oxygen consumption was linearly related to the local muscle oxygen extraction. However, the rate was doubled at simulated altitude compared with the sea level measurements.

Conclusions: 

NIRS is a suitable method to study muscle oxygenation during exercise and acute exposure to high altitude in a hypoxic chamber.

At 5000 m, muscle oxygen extraction, compared with rest levels, was about 50% lower than at sea level. Low saturation in arterial blood at high altitude, instead of local vasodilation capacity, can be the main limiting factor for oxygen delivery in active muscles.