Firstly, it tries to use the existing ATP (but it only lasts for about 1 minute), then phosphocreatine (which is used similarly to ATP), then glucogen, and finally amino acids, fatty acids,...
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Muscles do is to command the bones to move and you need food and energy to move around.
When any function has to be performed by body , muscles use energy. It helps in doing work.
The same place they get it from when they're used to do work ... the chemical potential energy that's extracted from food you eat, and stored in your body until the brain and muscles need it.
Your muscles get the "power" they need from the energy stored in food. When you digest food it gives you energy.
Muscles are metabolically very active.So they need lot of energy.
muscles need food and oxegen to work
Your body uses oxygen make energy, and muscles need energy to relax and contract, or flex. As you run, the demand for energy in your muscles increases, and so your lungs work harder to provide the oxygen your muscles are begging for. The result of higher demand for oxygen is faster deeper breaths.
When you exercise you use your muscles and your muscles contain Glycogen which could be considered your "energy source". during exercise your muscles use glycogen depleting your energy levels making you feel tired.
Muscles must work together because you need to move your body.
Human work converts chemical energy from food into mechanical energy through the contraction of muscles.
Muscles primarily use chemical energy stored in the form of adenosine triphosphate (ATP) to produce mechanical work. The chemical energy in ATP is converted into mechanical energy to enable muscle contraction and movement.