What are the most common sources of glucose needed for energy during exercise

Carbohydrates are the primary fuel when exercising and an essential nutrient for athletic performance. Our body runs most efficiently with a balance of protein, fat, and carbohydrates, but adequate carbohydrates are crucial for athletes.


  • The energy that nourishes muscle contractions and brain function
  • Stored energy for later use. (Any glucose that is not needed right away is stored in the muscles and liver in the form of glycogen.)
  • An alternative energy source to the protein used for energy

During physical exercise, stored carbohydrates or glycogen is converted into energy to provide the muscles, but this supply is not infinite. The number of carbohydrates stored in the body as glycogen depends on the diet and the athlete’s fitness level. Usually, total glycogen stores correspond to 400-700 grams (75-100g in the liver and 300-600 grams in the muscles). An athlete who eats a high carbohydrate diet and follows a solid nutritional protocol can increase these total carbohydrate reserves up to 880g. After approx. 60 to 90 minutes of training will deplete these fuels; therefore, refuel for more extended training.

Health Canada’s “Guide to Nutrition” recommendations recommend that 55 percent of the total energy in our diet should come from carbohydrates. It is recommended for elite athletes that 60% to 70% of the total energy consists of carbohydrates. Without sufficient carbohydrates, the body is forced to use more fat stores and protein from our muscles, which are less efficient energy-producing. Then, the quality of training and performance can be reduced. For athletes with a busy training plan, carbohydrate snacks and adequate fluid intake are essential to maintain muscle glycogen and optimal energy levels.

How many carbohydrates should we consume before, during, and after exercise?

In addition to eating enough carbohydrates daily, consuming carbohydrates before, during, and after exercise is essential to provide enough fuel and promote recovery. The exact timing and type of food consumed can be very individualized. It is recommended that athletes try different types of food to find out which one works best for them. The following table outlines the vital guidelines for carbohydrate, protein, and fluid intake before, during, and after exercise.

Why eat carbs?

Before: To replenish energy stores and expose fatigue. Aim for a light carbohydrate meal.

Below: To help maintain blood sugar to provide energy to muscles during exercise. Choose easily digestible carbohydrates and aim for 30-50 g of liquid or solid sources every 30 minutes. Exercise lasting more than 90 minutes demands extra carbohydrates to sustain your energy level.

After: To replenish your energy supply after training, eat carbohydrates and proteins within 60 minutes of completing the session.

What are the sources of carbohydrates and fluids for exercise?

Complex carbohydrates such as wholemeal pasta and cereals, legumes, fresh fruits, and starchy vegetables are excellent sources. They are low in fat and are packed with nutrients and fiber. They are nutritious, unprocessed sources of carbohydrates, proteins, fats, fiber, minerals, and vitamins that provide energy to your body. Although sports bars, gels, and drinks are fast, convenient energy sources, it is highly recommended to get energy from natural food sources and more economically. For example, a medium banana and a cup of fruit yogurt provide about 215 calories and 40 grams of carbohydrates. A Power bar adds 220 kcal and 48 grams of carbohydrates. Choose those without hydrogenated or saturated fats and additives or preservatives. It is beneficial to make your snacks.

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