Fatigue is a multifactorial process. Depletion of energy sources, including adenosine triphosphate (ATP), phosphocreatine (PCr), plus carbohydrates (CHO) like muscle glycogen and blood glucose can contribute to fatigue.

Does A High-Carbohydrate Breakfast Improve Performance?

KEY POINTSFatigue during prolonged heavy exercise is often associated with low or depleted muscle glycogen stores and with lowered blood glucose.

KEY POINTS■ Carbohydrate is the preferred fuel for most competitive sports；an inadequate supply of carbohydrate in the body often leads to poor performance.■ Carbohydrate ingestion during exercise increases blood glucose availability and maintains the ability of the body to use carbohydrate as fuel during exercise.When carbohydrate is consumed during exercise，glucose uptake by muscles is increased，and the breakdown of glycogen in the liver into blood glucose is reduced，thus saving liver glycogen until late in exercise.The use of muscle glycogen for energy is generally unaffected by carbohydrate feeding.However，during prolonged running，the breakdown of muscle glycogen may be slowed because the supply of blood glucose is improved when carbohydrate is consumed.These metabolic responses underlie the performance benefit that accompanies carbohydrate ingestion during exercise.■ There are some minor differences among glucose，sucrose，and maltodextrins in their effects on metabolism，but each of them can enhance performance when ingested in the appropriate quantity during exercise.Fructose alone is not an effective carbohydrate supplement because of its slow absorption and slow conversion by the body to glucose，but when small amounts of fructose are combined with other carbohydrates，fructose can be beneficial.■ Ingesting carbohydrate at a rate of 30-60 grams per hour can improve exercise erformance.A good way to achieve this carbohydrate intake is to consume 600-to-1200 ml(20-to-40 oz)of a sports drink during each hour of exercise.Consuming carbohydrate in a beverage provides an added benefit of preventing potentially harmful effects of dehydration on performance.