The Effect of Hypoxia on Muscle Glycogen Resynthesis in Man

The effect of hypoxia and muscle fibre type on the resynthesis of muscle glycogen was studied in three healthy subjects by means of needle biopsies. Biopsies were taken before and after exercise and after 5 h recovery. In control experiments subjects breathed air during the recovery phase whereas in the test experiments they breathed 10% oxygen in nitrogen during this time. Diet was controlled throughout the experiments and provided an excess of carbohydrate. Biopsies were assayed for total muscle glycogen and were studied histochemically, using microdensitometry on PAS stained sections as a measure of glycogen in individual fibres. Exercise depleted muscle glycogen to a mean of 26% of control values. After 5 h recovery the mean values had risen to 62% breathing air and 51% on 10% oxygen breathing but this difference was not significant. In biopsies taken after 5 h recovery breathing either air or 10% oxygen, there was a marked contrast in PAS staining between muscle fibre Type I and II, the Type II fibres being more heavily stained. This difference was confirmed by microdensitometry. The contrast was increased by hypoxia in all subjects but this effect did not reach levels of statistical significance. It is concluded that under these experimental conditions the overall resynthesis of muscle glycogen is not significantly affected by hypoxia. It is shown that Type II fibres resynthesise significantly more rapidly than Type I under both normoxic and hypoxic conditions. Hypoxia may enhance this difference in rate of resynthesis.