What do muscles use for energy during exercise?

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Nutrition Blog

While most people know that aerobic exercise is good for the heart and that resistance training helps build lean body mass, most people don’t fully understand how these different types of exercise cause very different responses within our bodies. It is critical to have a basic understanding of how our body uses energy during different forms of exercise. This is in order to design an effective exercise programme.

Energy and muscles

It is a well-known fact that our bodies need a constant supply of energy to function properly. This is in order 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. This includes carbohydrates, protein and fats.

The energy stored in these substrate molecules is then chemically released into the cells of your body. It is then 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).

What Type of Energy Does the Body Burn First During Exercise?

Your body functions off of three main energy systems. These are:

  • Your ATP-PCr system whichh is involved in short-term anaerobic energy.
  • The glycolytic system in your body produces energy through the breakdown of carbohydrates stored in your muscles and liver.
  • Your body’s aerobic system uses oxygen and fat to produce slow, yet long-lasting energy.

It is during most types of exercise that your body uses some blend of all three energy systems at the same time. However, it may emphasise the use of one over another based on the needs of your body and the type of activity you are performing.

TP-PCr System

The most simple of the three energy systems is the ATP-PCr system. The term ‘ATP’ stands for adenosine triphosphate. This is the chemical form of raw energy in your body. The term ‘PCr’ stands for phosphocreatine. This is a compound that is attached to every ATP molecule.

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Inside your skeletal muscles, when a muscle fibre receives a signal from a nerve to contract, the ATP-PCr molecules separate from one another. This is as a result of a complex chemical reaction. The separation of this releases the energy which causes a muscle to contract. During very short duration exercise – that lasts less than 10 seconds – this energy system is used. Examples are a quick jump or a sprint.

Glycolytic System

Glucose, or sugar, is stored in your liver and skeletal muscles. When needed, your muscles will break glucose down using special enzymes. They will eventually convert sugar into ATP.

The ATP is then used for muscle contraction. This system is best used for activities that take less than two minutes to perform at a high intensity. This comprises sprints in addition to other bouts of short yet intense exercise.

Aerobic System

The aerobic system mainly uses fat for energy production. However, it can also use stored carbohydrates and proteins. Aerobic means “with oxygen”. This means that oxygen is required in the process of breaking down fat stores for energy. Fat molecules are pulled from various stores around the body. They are then converted to ATP through a complex chemical reaction. This takes place inside your muscles. Large amounts of continuous energy are yielded by your aerobic system. This is ideal for long-duration activities such as long runs or bike rides.

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