Carbohydrate ingestion and single muscle fibre glycogen metabolism during prolonged running in man. Tsintzas, Orestis-Konstantinos, Clyde Williams, Leslie Boobis and Paul Greenhaff. Department of Physical Education, Sports Science and Recreation Management, Loughborough University, Loughborough, Leics. LE11 3TU, England, UK, Sunderland General Hospital, Sunderland SR4 7TP, UK, Department of Physiology and Pharmacology, Nottingham University Medical School, Nottingham, NG7 2UH.
APStracts 3:0234A, 1996.
In previous studies, muscle glycogen degradation in different fibre types during prolonged exercise was examined using qualitative or semi-quantitative histochemical methods. The aim of this study was to examine the effect of carbohydrate (CHO) ingestion on glycogen degradation in type I and type II muscle fibres during prolonged running using a quantitative biochemical method. To this end, eight male subjects ran at 70% VO 2 max to exhaustion on a motorised treadmill on two occasions, one week apart. On each occasion the subjects ingested 8 ml/kg body weight (bw) of either placebo (PL) or a 5.5% carbohydrate-electrolyte solution (CHO-E) immediately before the start of the run and 2 ml/kg bw every 20 min thereafter. Needle biopsy samples were obtained from the vastus lateralis muscle before and after each trial, and also at the time coinciding with placebo exhaustion (TPE) in the CHO-E trial. Running time to exhaustion was longer (P < 0.01) in the CHO-E trial compared with the PL trial (132.4 +/- 12.3 min vs 104.3 +/- 8.6 min, respectively). A higher mixed muscle glycogen concentration was observed at TPE in the CHO-E trial when compared with exhaustion in the PL trial (125.6 +/- 22.3 mmol/kg dry wt vs 59.8 +/- 7.9 mmol/kg dry wt, P < 0.05, respectively). This sparing of muscle glycogen was almost totally restricted to type I fibres (87.1 +/- 18 mmol/kg dry wt vs 31.6 +/- 10.3 mmol/kg dry wt, P < 0.01, respectively). Therefore, since fatigue in both the PL and CHO-E trials coincided with low glycogen concentrations in type I fibres (31.6 +/- 10.3 mmol/kg dry wt and 28.1 +/- 7.1 mmol/kg dry wt, respectively), it is proposed that carbohydrate ingestion improved endurance capacity by contributing to oxidative ATP production specifically in type I fibres and by doing so delayed the development of glycogen depletion in this fibre type. 

Received 7 August 1995; accepted in final form 30 January 1996.
APS Manuscript Number A867-5.
Article publication pending Am. J. Physiol. (Journal of Applied Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 May 96