Carbohydrate feeding prior to prolonged exercise: effect of the
glycemic index on muscle glycogenolysis and exercise performance.
Febbraio, Mark A., and Kathryn L. Stewart.
Department of Human Movement Science, Royal Melbourne Institute of
Technology, Bundoora, 3083, Australia
APStracts 3:0209A, 1996.
This study examined the effect of pre-exercise carbohydrate ingestion
on muscle carbohydrate metabolism and performance during prolonged
exercise. Six endurance trained men performed three exercise trials
on a cycle ergometer after ingesting either a high glycemic index
(HGI), low glycemic index (LGI), or placebo (CON) meal 45 min prior
to exercise. During each trial subjects cycled at a workload
corresponding to 70% peak for 120 min followed by a 15 min
performance cycle where total work (kJ) was measured. Ingestion of
HGI resulted in an elevated (P<0.01) blood glucose concentration
15 min after ingestion compared with LGI and CON but there were no
differences in the glycemic responses of the meals thereafter,
despite plasma insulin concentration being higher (P<0.01)
throughout the rest period following ingestion of HGI compared with
LGI and CON. Plasma free fatty acid concentrations were lower
(P<0.05) throughout exercise in HGI compared with LGI and CON.
In addition, concentrations of this metabolite were lower
(P<0.05) during the first hour of exercise in LGI compared with
CON. Despite these results, no differences were observed in either
the rate of muscle glycogen utilization during submaximal exercise or
work output during the performance cycle when comparing the three
trials. These results demonstrate that pre-exercise carbohydrate
ingestion has no effect on muscle glycogen utilization or exercise
performance irrespective of the glycemic or insulinemic responses of
the ingested meals.
Received 29 January 1996; accepted in final form 4 April 1996.
APS Manuscript Number A121-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 May 96