What is the primary fuel for an activity that is low intensity and has lasted more than 20 minutes?

What you eat really does have an impact on how effectively and efficiently you can provide energy to your working muscles. The body converts food into adenosine triphosphate (ATP) for fuel through several different energy pathways. Understanding these systems can help you train and eat more effectively, and boost your overall sports performance.

Because the body cannot easily store ATP (and what is stored gets used up within a few seconds), it is necessary to continually create ATP during exercise. In general, the two major ways the body converts nutrients to energy are:

Aerobic metabolism (with oxygen)
Anaerobic metabolism (without oxygen)

These two pathways can be further divided into three main energy systems (listed below). Most often it's a combination of energy systems that supply the fuel needed for exercise. The intensity and duration of the exercise determine which method gets used when.

The ATP-CP energy pathway (sometimes called the phosphagen system) is an anaerobic pathway because it doesn't require any oxygen to create ATP. The "CP" stands for creatine phosphate, a naturally occurring compound that enables short bursts of energy.

The ATP-CP pathway supplies about 10 seconds worth of energy and is used for short bursts of exercise, such as a 100-meter sprint.

This pathway first uses up any ATP stored in the muscle (about 2 to 3 seconds worth). Then it uses creatine phosphate (CP) to recycle ATP until the CP runs out (another 6 to 8 seconds). After the ATP and CP are used, the body will move on to either aerobic or anaerobic metabolism (glycolysis) to continue to create ATP to fuel exercise.

Glycolysis is both an anaerobic and anaerobic system which creates ATP exclusively from carbohydrates, with lactic acid being a byproduct. Anaerobic glycolysis provides energy by the (partial) breakdown of glucose without the need for oxygen.

Glycolosis is considered both an aerobic and anaerobic pathway. This process produces energy for short, high-intensity bursts of activity lasting no more than several minutes.

After several minutes, the lactic acid build-up reaches a threshold known as the lactate threshold (LT). When you reach this threshold, you experience muscle pain, burning, and fatigue, making it difficult to keep exercising at this intensity. However, training can increase the threshold.

Aerobic metabolism fuels most of the energy needed for long duration activity. It uses oxygen to convert macronutrients (carbohydrates, fats, and protein) to ATP. This system is a bit slower than the anaerobic systems because it relies on the circulatory system to transport oxygen to the working muscles before it creates ATP.

Aerobic metabolism is used primarily during endurance exercise, which is generally less intense and can continue for long periods of time.

During exercise, an athlete will move through these metabolic pathways. As exercise begins, ATP is produced via anaerobic metabolism. With an increase in breathing and heart rate, there is more oxygen available and aerobic metabolism begins and continues until the lactate threshold is reached and anaerobic metabolism kicks in again.

Sports nutrition is built upon an understanding of how macronutrients, such as carbohydrates, fat, and protein, contribute to the fuel supply needed by the body to perform. Macronutrients contribute to the process in different ways.

Each macronutrient has unique properties that determine how it gets converted to ATP.

Carbohydrate is the main nutrient that fuels moderate to high intensity exercise.
Fat can fuel low-intensity exercise for long periods of time.
Protein is generally used to maintain and repair body tissues and is not normally used to power muscle activity.

Because your body uses different pathways to create energy, and each pathway relies on different macronutrients, it's important to consume fat, carbohydrates, and protein in your diet.

Nutrients get converted to ATP based on the intensity and duration of activity, with carbohydrate as the main nutrient fueling exercise of a moderate to high intensity, and fat providing energy during exercise that occurs at a lower intensity.

Fat is a great fuel for endurance events, but it is simply not adequate for high-intensity exercises such as sprints or intervals. If exercising at low intensity (or below 50% of max heart rate), you have enough stored fat to fuel activity for hours or even days, as long as there is sufficient oxygen to allow fat metabolism to occur.

As exercise intensity increases, carbohydrate metabolism takes over. It is more efficient than fat metabolism but has limited storage capacity. Stored carbohydrate (glycogen) can fuel about two hours of moderate to high-level exercise. After that, glycogen depletion occurs (stored carbohydrates are used up). If that fuel isn't replaced, athletes may hit the wall or "bonk."

An athlete can continue moderate to high-intensity exercise for longer by simply replenishing carbohydrate stores during exercise. This is why it is critical to eat easily digestible carbohydrates during moderate exercise that lasts more than a few hours. If you don't take in enough carbohydrates, you will be forced to reduce your intensity and tap back into fat metabolism to fuel activity.

In fact, carbohydrates can produce nearly 20 times more energy (in the form of ATP) per gram when metabolized in the presence of adequate oxygen than when generated in the oxygen-starved, anaerobic environment that occurs during intense efforts (sprinting).

The three main energy systems the body uses to create ATP are: the ATP-CP energy pathway (or phosphagen system), glycolysis, and aerobic metabolism.

The ATP-CP energy system powers very short bursts of exercise, and supplies up to 10 seconds of power and energy to your body.

The ATP-CP energy system works by using ATP and creatine phosphate (CP) to give your body fuel. While ATP provides about 2 to 3 seconds of energy, the CP provides 6 to 8 seconds. Together, they can provide enough energy for a quick 10-second sprint.

The ATP-CP, or phosphagen, system is the first energy pathway that is used during exercise. This energy pathway is quickly depleted and allows for a quick burst of fuel to lift heavy weights or perform a short sprint.

Energy pathways in the body can adapt as you increase your fitness. With appropriate training, these energy systems become more efficient and allow you to exercise at a higher intensity for longer periods of time.

Carbohydrate is the primary fuel for most types of exercise and the most important nutrient for athletic performance. Our body runs most efficiency with a balance of protein, fat and carbohydrates, but adequate carbohydrate is a key source of energy for athletes.

Carbs provide…

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

During physical exercise stored carbohydrate or glycogen is converted into energy to fuel the muscles, but this supply is not endless. The amount of carbohydrate that can be stored in the body as glycogen depends on diet and the athlete’s conditioning level. Typically total glycogen stores equal 400-700 grams (75-100g in the liver and 300-600g in the muscles). An athlete consuming a high carbohydrate diet and following a solid nutrition protocol can increase these total carbohydrate reserves up to 880g. After about 60 to 90 minutes of exercise these fuels will become depleted; therefore the need to refuel for longer training.

Health Canada's "Guide for Nutrition" Recommendations advises that 55 per cent of the total energy in our diet should come from carbohydrates. For elite athletes, it is recommended that 60% to 70% of total energy be comprised of carbohydrates. Without adequate dietary carbohydrate the body is forced to rely more on fat stores and protein from our muscles, which are less efficient energy-producing pathways. As a result, the quality of training and performance may diminish. For athletes with a busy and rigorous training schedule, both carbohydrate snacks and adequate fluid intake are essential to maintain muscle glycogen and to sustain optimal energy levels.

How much carbohydrate and fluid should we consume before, during and after exercise?Figure skaters, for example, must have enough energy to endure long aerobic activities and have split-second power surges to jump. On top of eating adequate carbohydrates daily, taking in carbohydrate before during and after exercise is essential to provide enough fuel and promote recovery. The following table outlines the key guidelines for carbohydrate, protein and fluid intake pre-, during and post-training. It is important to note that the exact timing and type of food to consume can be very individualized. It is recommended that athletes trial various types of food to find out which works best for them.

Why eat carbohydrate?

Before: To top up energy stores and delay fatigue. What you eat depends on how much time you have, but aim for a light carbohydrate meal.

During: To help to maintain blood sugar to fuel muscles during exercise. If your training session lasts longer than 90 minutes you will need additional carbohydrates to maintain energy levels. Choose easy to digest carbohydrates and aim for 30-50 g of liquid or solid sources every 30 minutes.

After: For replenishment of your energy supply after exercise, which helps guarantee the ability to last longer in the next training session or event. For optimal recovery and replenishment of glycogen stores, eat carbohydrates and protein within 60 minutes of completing your session.

When	How much?	For Example
Pre-training fuel1-2 hours before* easy to digest * low fat	Carbohydrate 2 g/kgProtein 10-15 g Fluids 500 ml	1 cup chocolate soy milk + 1 cup water + banana Or, 1 Granola bar + 1 low fat yogurt + 1 cup water
During training fuels	600-1200 ml fluid/ hour(3-4 large gulps every 15-20 minutes) Carbohydrate 30-60 g/hr over 60-90 minutes	Water or sports drink 1 -2 water bottles (~500 ml each)
Post-training fuel * within 1 hour of session	carbohydrate 1 g/kgprotein 15-20 g fluids 600-1200 ml	1 tetra pack soy milk + banana + 2 cups water Or, 1 cliff bar + apple + 2 cups water Or, 1 Kashi granola bar + 1 cup chocolate milk + 1 cup water

More than one training session or game….For sports where there is more than one daily training session or back-to-back events scheduled follow these additional guidelines to ensure optimal refuelling and recovery between:

When	What?	For Example
30 minutes between games	Carbohydrate	Juice or sports drink
1-2 hours between games	Carbohydrate	BananaJuiceSports drink Energy bar
> 2 hrs (recovery nutrition)	Carbohydrate & Protein	1 cup chocolate milk + Nature Valley granola bar + 1 cup water Or Cliff Bar + ¾ cup yogurt + 1-2 cups water Or Peanut Butter & Jam sandwich + 1 cup soy milk Or 1 Kashi Granola Bar + 1 banana + 1-2 cups water Or 1 Apple + energy bar + 1-2 cups water Or ¾ cup yogurt + 0.25 cup dried fruit + 1-2 cups water

What are sources of carbohydrate and fluids for exercise?
Complex carbohydrates such as whole grain pasta and cereals, legumes, fresh fruit and starchy vegetables are excellent sources because they release energy slowly, are low in fat, and are packed with nutrients and fibre. Although sports bars, gels and drinks are quick, convenient sources of energy, obtaining your energy from natural sources of food is highly recommended and more economical. For example, a medium banana and one cup of fruit yogurt supply approximately 215 calories and 40 grams of carbohydrate. A Power Bar supplies 220 kcal and 48 grams of carbohydrate. If you choose sports foods, choose those without hydrogenated or saturated fats and without additives or preservatives. There is an advantage to making your own snacks they are nutritious, unprocessed sources of carbohydrate, protein, fat, fibre, minerals, and vitamins that energize your body.

Homemade Energy Bars 1 cup old fashioned oats ½ cup unsalted raw peanuts ½ cup pumpkin seeds ½ cup sunflower seeds ¼ cup semi-sweet coconut ½ cup raisins 1/2 cup ¼ cup dried cranberries ¼ cup Family flaxseeds 1 cup bran flakes 1 ½ cup crispy rice cereal ¾ cup smooth peanut butter ¾ cup honey 2 tsp vanilla

Mix dry ingredients, mix wet ingredients. Mix together. Spread in pan. Bake at 350°F (180°C). Cool & cut into 20 bars.

Take Action

Plan ahead! Prepare your daily snack-pack the night before. Pack it full of nutritious carbohydrate-rich snacks such as a whole grain bagel with peanut butter, yogurt, fig bars, bananas, orange slices, graham crackers and granola bars.
Develop a complete nutrition training plan. Don't just eat and keep well hydrated during competition. Practice fuelling during training so you are accustomed to it for your events. Experiment with different quantities and sources of carbohydrate (foods and fluids) during exercise to determine what keeps your body performing at optimal levels.
Always carry a water bottle and take regular sips during activity. Ask your coach to remind you.

Note: With even a 2 percent dehydration work capacity drops by 10-20 percent.

viaSport Return to Sport

As of March 11, 2022:

Masks are no longer required.
- Individual businesses and event organizers can choose to continue requiring masks on their premises.
- Reminder to the sport community to be respectful of people's differing comfort levels and that as we transition into this period, people may still choose to wear their mask.

As of April 8, 2022, proof of vaccine will no longer be required.

Individual businesses and event organizers can choose to continue requiring proof of vaccination for entry.
Additional guidance may be in place. See the Province of B.C.'s provincial restrictions page for more information.

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