Human Physiology

Abstract

The purpose of the experiment, which had ethical committee approval, was to investigate for the first time the effect of carbohydrate (CHO) ingestion on post-exercise glycogen resynthesis, measured simultaneously in human liver and skeletal muscle, and subsequent exercise capacity. Ten healthy, well-trained and familiarized males cycled at 70 % maximal oxygen uptake for 83 ± 8 min, on six separate occasions. Subjects then ingested 1 g (kg body massr l (BM) glucose (18'5% w/v; condition A) or sucrose (18'5% w/v; B), or an equivalent volume of placebo (control; C). Over the following 4 h, muscle and liver glycogen content was measured by 13C MRS (occasions 1-3).Liver spectra and volume measurements were obtained pre-and post-exercise, within 30 min after CHO ingestion and hourly thereafter. Muscle spectra and volume measurements were obtained from 30-60 min and hourly thereafter. Subsequent exercise capacity was measured on occasions 4-6. To do this, the above procedures were repeated with the omission of the glycogen measurements and, at the end of the 4 h recovery period, exercise time to exhaustion was measured. Values are given as means ± S.E.M. Data were analysed by two-way repeated measures ANOVA. Liver and muscle glycogen content declined during the initial bout of exercise by ~60 % in all trials (P < 0'05). No glycogen was resynthesized during the control trial. Liver glycogen resynthesis was evident following glucose (13 ± 8 g) and sucrose (25 ± 5 g) ingestion, both of which were different from control (P < 0'01).A relationship between the CHO load (g) and change in liver glycogen content (g) was evident after 30, 90, 150 and 210 min of recovery (r = 0'59-0'79, P < 0'05). Furthermore, a modest relationship existed between the change in liver glycogen content (g) and subsequent exercise capacity. Significant changes in muscle glycogen resynthesis were not demonstrated, due perhaps to the small CHO load and the large inter-individual variation in glycogen measurements.Peak blood glucose was highest following glucose ingestion (P < 0'05). Ammonia production tended to be lower during exercise bout 2 following CHO ingestion (P = 0'069). No significant difference in exercise capacity was found (C: 35 ± 5; A: 40 ± 5; B: 46 ± 6 min).Therefore, 1 g (kg BMr 1 glucose or sucrose is sufficient to initiate post-exercise liver glycogen resynthesis, which Journal of Physiology (1999) It has been reported than an increase in cellular creatine (Cl') availability can increase lean tissue mass (Kreider et al. 1988) and stimulate mitochondrial respiration (Wyss et al. 1992). As a decrease in cellular Cr availability has been implicated in the disruption of energy metabolism in failing myocardium (Conway et al. 1998), this raises the possibility that Cr supplementation may be beneficial in cardiac disease states. However, there are presently little or no data available concerning the effects of Cr supplementation on myocardial creatine accumulation and creatine transporter mRNA (CrT mRNA) content. Therefore, the aim of t...