The effects of a glycogen-loading regimen on the capacity to perform anaerobic exercise

Abstract

The effect of a pattern of exercise and dietary modifications, which was designed to produce alterations in the muscle glycogen content, on the capacity to perform anaerobic exercise was investigated. Six young male subjects worked to exhaustion on a bicycle ergometer at a supramaximal work load equivalent to 104 +/- 5% of VO2max after a normal diet, after a carbohydrate (CHO)-free diet following prolonged exhausting exercise, and after a high-CHO diet. This regimen has previously been shown to cause changes in the glycogen content of the working muscle. Mean work time for subjects on the first test was 4.87 +/- 1.07 min (mean +/- SD). After the low-CHO diet, the time for which work could be maintained was reduced in an increase to 3.32 +/- 0.93 min, whereas administration of the high-CHO diet resulted in an increase to 6.65 +/- 1.39 min. The resting blood lactate concentration was lower than normal following the low-CHO diet and higher than normal following the high-CHO diet. Post exercise blood lactate concentrations reached a peak between 2 and 6 min after exhaustion and again were lower (8.60 +/- 1.58 mmol/l) after the low-CHO diet and higher (12.86 +/- 1.42 mmol/l) after the high-CHO diet than after performing the same intensity of work to exhaustion on a normal diet (11.66 +/- 1.16 mmol/l). The rate of lactate accumulation appeared to be approximately the same during exercise under all three dietary conditions. If this is the case, it suggests that the alterations in endurance capacity do not result from changes in the rate of anaerobic glycolytic energy production, but possibly from a change in the total capacity of the system.

Two weeks of watermelon juice supplementation improves nitric oxide bioavailability but not endurance exercise performance in humans

“…We observed that watermelon juice supplementation and the apple juice placebo tended to increase time-to-exhaustion compared to the control condition. This might be linked to the chronic carbohydrate consumption in both the juice concentrate conditions compared to the control conditions [53]. There is also evidence that chronic carbohydrate consumption does not improve performance during short-duration high-intensity exercise [see 54 for review] and the general consensus is that carbohydrate supplementation is not necessary to optimise performance during events < 30 min in duration [55].…”

Pre-exercise carbohydrate and fat ingestion: effects on metabolism and performance

“…Some studies have observed enhanced performance with elevated muscle glycogen concentrations after increased dietary carbohydrate intake (Maughan and Poole, 1981;Maughan et al, 1997), while others have observed no benefit of elevated pre-exercise muscle glycogen (Vandenberghe et al, 1995;Hargreaves et al, 1997). In studies by Maughan and colleagues, the differences in performance were most obvious at the extremes of diet and may have been due as much to deleterious acid-base disturbances following consumption of a high fat-protein diet as to increased muscle glycogen availability following the high carbohydrate diet (Maughan et al, 1997).…”

Time to exhaustion during severe intensity running: response following a single bout of interval training

“…It is possible that time to exhaustion is influenced by substrate availability, and an increased metabolism of fat in the moderate intensity run one hour following the TS indicates a depletion of muscle glycogen stores. A previous study has demonstrated the importance of muscle glycogen stores prior to exercise for short duration performance (Maughan and Poole, 1981).…”