Carbohydrate Dependence During Prolonged, Intense Endurance Exercise.
Hawley JA1,2, Leckey JJ3.
Author information
1The Mary MacKillop Institute for Health Research, Centre for Exercise and Nutrition, Australian Catholic University, Locked Bag 4115, Fitzroy, VIC, 3065, Australia. John.hawley@acu.edu.au.
2Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK. John.hawley@acu.edu.au.
3The Mary MacKillop Institute for Health Research, Centre for Exercise and Nutrition, Australian Catholic University, Locked Bag 4115, Fitzroy, VIC, 3065, Australia.
Abstract
A major goal of training to improve the performance of prolonged, continuous, endurance events lasting up to 3 h is to promote a range of physiological and metabolic adaptations that permit an athlete to work at both higher absolute and relative power outputs/speeds and delay the onset of fatigue (i.e., a decline in exercise intensity).
To meet these goals, competitive endurance athletes undertake a prodigious volume of training, with a large proportion performed at intensities that are close to or faster than race pace and highly dependent on carbohydrate (CHO)-based fuels to sustain rates of muscle energy production [i.e., match rates of adenosine triphosphate (ATP) hydrolysis with rates of resynthesis].
Consequently, to sustain muscle energy reserves and meet the daily demands of training sessions, competitive athletes freely select CHO-rich diets.
Despite renewed interest in high-fat, low-CHO diets for endurance sport, fat-rich diets do not improve training capacity or performance, but directly impair rates of muscle glycogenolysis and energy flux, limiting high-intensity ATP production.
When highly trained athletes compete in endurance events lasting up to 3 h, CHO-, not fat-based fuels are the predominant fuel for the working muscles and CHO, not fat, availability becomes rate limiting for performance.
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