Pre-exercise muscle glycogen content affects metabolic regulation
during exercise despite maintenance of hyperglycaemia..
Weltan, Sandra M., Andrew N. Bosch, Steven C. Dennis, and Timothy D.
Noakes.
Department of Physiology, University of Cape Town Medical School,
Observatory 7925, South Africa. Phone: (27) - (21) - 686-7330, Fax:
(27) - (21) - 686-7530, E-mail: abosch@sports.uct.ac.za
APStracts 4:0216E, 1997.
Trained cyclists with low muscle glycogen (LGH; n=8) or normal
glycogen (NGH; n=5) exercised for 145 minutes at 70% of VO2 max
during a hyperglycaemic clamp. RER was higher in NGH than LGH and
free fatty acid concentrations (FFA) lower in NGH than LGH. Areas
under the curve for insulin and lactate were lower in LGH than NGH.
Total glucose infusion (I) and total glucose oxidation (Gox) were not
different between NGH and LGH and Gox amounted to 65% and 66% of I in
NGH and LGH, respectively. Rates of glucose oxidation rose during
exercise, reaching peaks of 9.2+/-1.7 and 8.3 +/-1.1mmol/min in NGH
and LGH, respectively. Muscle glycogen disappearance was greater in
NGH than LGH. Thus: i) low muscle glycogen content does not cause
increased glucose oxidation even during hyperglycaemia; instead there
is an increase in fat oxidation, ii) there is an upper limit to rate
of glucose oxidation during exercise with hyperglycaemia irrespective
of muscle glycogen status and iii) net muscle glycogen utilisation is
determined by muscle glycogen content at the start of exercise even
during hyperglycaemia.
Received 11 November 1996; accepted in final form 22 September
1997.
APS Manuscript Number E567-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 7 October 1997