Which of the adaptations to a period of acclimatisation to chronic hypoxia are important in determining skeletal muscle performance and fatiguability?

Abstract

Patients with oxygen-deficient diseases! suffer from chronic hypoxia and exercise intolerance. However it is not clear whether this is due to muscular dysfunction or changes in oxygen delivery. Acclimation to chronic hypoxia involves increased haematocrit, angiogenesis and changes in skeletal muscle fibre-type. The objective of this study was to investigate the effect of changing oxygen delivery by isovolaemic haemodilution on muscle fatigue, in normoxic and chronic hypoxic rats.
Arterial blood pressure, femoral blood flow and tension in the extensor digitorum longus muscle were recorded in four groups of alfaxananaesthetised male Wistar rats. The peroneal nerve was stimulated for five successive 3 min periods at 15Hz. The treatments encompassed haemodilution, a total of 9ml sequestered between consecutive stimulations, in normoxic and hypoxic animals, acclimated to 12% O\(_2\) for three weeks that inspired oxygen at 8% and 12%.
Consistent response profiles were generated by the time controls; contractions were associated with a ~1200g.s\(^-\)\(^1\) muscle performance and ~40% fatigue. Haemodilution had no effect on these responses. The chronic hypoxic group (12%O\(_2\)) fatigued ~10% more than haemodilution controls at matched oxygen delivery. It is proposed that muscular adaptations evoked by 12%O\(_2\) acclimation play a greater role in mechanisms limiting exercise tolerance than vascular adaptations.