The most important fuel source for exercise is carbohydrate in the form of glucose.
Glycogen is the storage form of glucose in muscle and because glycogen storage is limited, it can be depleted. The depletion can occur in 1-2 hours of intense activity and can significantly compromise endurance exercise performance.
To help maintain a steady supply of energy, the ACSM and AND recommend that athletes consume 30g to 60g or more of carbohydrates (120-240 calories) per hour of exercise. It is suggested the source has less than 5g of fat, 5g of fiber and 5g of protein. Ultra-endurance athletes can require more carbohydrates.
In addition, when pre-fueling for endurance, easily digested, low-fiber complex carbohydrates in the 60 minutes prior to a workout are best.
These are general guidelines. To calculate guidelines that are specific to you and the type of exercise you do, scroll further down the page.