The body uses carbohydrates, proteins and fats as energy during exercise, with carbohydrates the body's preferred energy source. The amount of carbohydrates burned during exercise depends on factors such as the type of exercise, the duration of the exercise and the intensity of the exercise.
Sources
Complex carbohydrates such as oatmeal, sweet potatoes, potatoes, yams, whole grain rice, whole grain bread, and whole grain pasta provide slow-release energy. These carbohydrates are broken down and stored in the liver or muscles as glycogen ready to be used to power your workouts.
Simple carbohydrates from refined grains such as white rice, white bread, packaged breakfast cereals, fruit juice, sugar and honey break down swiftly into glucose by the body and provide quick energy. If this energy is not going to fuel exercise, it becomes a surplus, which is transported by insulin to your fat stores and can result in unwanted weight gain.
Short Intense Exercise
Glycogen stored in the liver and muscles is the primary source of energy for short intense bouts of exercise such as weightlifting, sprinting or explosive activities that involve rapid contraction of the muscles. If glycogen stores become depleted, use a sports drink that contains simple carbohydrates. This will convert into glucose to be readily used by your muscles.
Cardiovascular Exercise
Between 50 and 60 percent of energy used in low intensity cardiovascular exercise such as brisk walking, jogging, swimming or cycling comes from fat. Carbohydrates are mainly used during the first few minutes. The website ExRx.net says it takes 20 to 30 minutes of continuous cardiovascular exercise to use 50 percent carbohydrates and 50 percent fat. If you increase the intensity, such as incorporating short bursts of sprinting into a 30-minute jog, the energy contribution from carbohydrates increases as your muscles contract harder and faster.
Carbohydrate Depletion
Your muscles continue to use carbohydrates stored in the muscles and liver as glycogen for energy during cardiovascular exercise. If you exercise for more than 90 minutes, your might use up your stores of glycogen.
Your muscles will be compelled to use protein as energy, which will eventually lead to a loss of muscle tissue. If you intend to do long cardiovascular sessions, eat plenty of complex carbohydrates a few hours before you exercise. This is called carb-loading and helps ensure you do not use up your stores of glycogen during prolonged periods of exercise.
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