The Effects of Carbohydrate Loading on Muscle Glycogen Content and Cycling Performance

Abstract

This study compared the effects of supplementing the normal diets of 8 endurance-trained cyclists with additional carbohydrate (CHO), in the form of potato starch, for 3 days on muscle glycogen utilization and performance during a 3-hr cycle ride. On two occasions prior to the trial, the subjects ingested in random order either their normal CHO intake of 6.15 ± 0.23 g/kg body mass/day or a high-CHO diet of 10.52 ± 0.57 g/kg body mass/day. The trial consisted of 2 hr of cycling at ~75% ofwith five 60-s sprints at 100%at 20-min intervals, followed by a 60-min performance ride. Increasing CHO intake by 72 ± 9% for 3 days prior to the trial elevated preexercise muscle glycogen contents, improved power output, and extended the distance covered in 1 hr. Muscle glycogen contents were similar at the end of the 3-hr trial, indicating a greater utilization of glycogen when subjects were CHO loaded, which may have been responsible for their improved cycling performance.

Complex systems model of fatigue: integrative homoeostatic control of peripheral physiological systems during exercise in humans

“…Re-analysis of a previous study from this unit 22 adds further support to the existence of a ''glycostat''. In that study, subjects were asked to cycle for two hours at 75% VO 2 peak, during which time they also completed five 60 second sprint bouts.…”

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

“…The mechanisms that allow trained individuals to rapidly increase muscle glycogen stores remain to be elucidated, but are likely to be related to their higher GLUT-4 concentrations and glycogen synthase activities (Hickner et al, 1997). Despite a greater reliance on muscle glycogen when pre-exercise concentrations are elevated (Gollnick et al, 1972;Bosch et al, 1993;Hargreaves et al, 1995), increased dietary carbohydrate in the 1-7 days before exercise is generally associated with enhanced performance when exercise duration exceeds about 90 min (Galbo et al, 1979;Brewer et al, 1988;Fallowfield and Williams, 1993;Rauch et al, 1995;Hawley et al, 1997b;Walker et al, 2000), probably due to a delay in the point at which muscle glycogen availability is limiting for optimal exercise performance. The largest effects are observed during exercise trials to exhaustion (often referred to as endurance 'capacity') and, while still apparent, they are smaller in magnitude during tests of endurance 'performance' that are not open-ended such as total work output in a given time or time taken to complete a certain distance or amount of work (Jeukendrup et al, 1996).…”

Fuel utilisation during prolonged low-to-moderate intensity exercise when ingesting water or carbohydrate

“…It is now well established that both carbohydrate (CHO) loading before exercise [1,2,18,24] and CHO ingestion during exercise [9,10] can enhance endurance exercise at >70% of maximum 0 2 consumption (l)'O2, max). Depending on the subject's preceding nutritional status, fatigue during prolonged exercise coincides with either a reduction in the conversion of liver glycogen to plasma glucose [Glu], leading to hypoglycaemia [9] or, in non-fasted subjects, a critically low (22 + 4 mmol/ kg wet wt.)…”