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How does my body use energy during exercise?

Our bodies need a constant supply of energy to function properly to maintain health and internal balance. The food we eat is what provides our cells with the needed energy to survive and function properly. But before food can become a usable form of energy it has to be converted into smaller units called substrates, including carbohydrates, proteins, and fats. The energy stored in these substrate molecules is then chemically released in cells and stored in the form of a high-energy compound called adenosine triphosphate (ATP). When the chemical bonds that hold ATP together are broken, energy is released for cellular work (such as performing muscle contraction).

Dr. Vonda Wright, MD
Orthopedic Surgery
Muscles get energy to propel you along by tapping into your muscle glycogen (the form of carbohydrates in which carbohydrates are stored). When these are diminished, you start to depend on your blood glucose to keep going. Blood glucose is derived from carbohydrates, fat, and protein. If you can't maintain your blood sugar levels, your performance will flounder.
Carbohydrates are the largest contributor to the energy pool. Fat contributes to your energy pool over a wide range of exercise intensities but decreases as you exercise harder because carbs will contribute more. Proteins contribute less than 5 percent of energy used during exercise but contribute to your overall pool during rest. The exception to this is during endurance exercise, when your liver begins to synthesize energy from protein.
Fitness After 40: How to Stay Strong at Any Age

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Fitness After 40: How to Stay Strong at Any Age

It's one of the undeniable facts of life. After we reach a certain age, our bodies change. No matter how fit we may have been at 20, we're very different people after 40. But growing older doesn't...

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.