How many calories do I need a day?

This depends on your age, body size, sport and training program. For example, a 250-pound weight lifter needs more calories than a 98-pound gymnast. Exercise or training may increase calorie needs by as much as 1,000 to 1,500 calories a day. The best way to determine if you’re getting too few or too many calories is to monitor your weight. Keeping within your ideal competitive weight range means that you are getting the right amount of calories.

What do muscles use for energy during exercise?

Most activities use a combination of fat and carbohydrate as energy sources. How hard and how long you work out, your level of fitness and your diet will affect the type of fuel your body uses. For short-term, high-intensity activities like sprinting, athletes rely mostly on carbohydrate for energy. During low-intensity exercises like walking, the body uses more fat for energy.