Question

Why an exercised body's muscles are fit????

Answer 1

As mentioned, your heart rate increases with physical activity to supply more oxygenated blood to your muscles. The fitter you are, the more efficiently your heart can do this, allowing you to work out longer and harder. As a side effect, this increased efficiency will also reduce your resting heart rate. Due to this our body get healthy

Answer 2

because on exorcising they (exercising muscle's) get their required amount of nutrients by circulation of blood.
so exercise's muscles fit.
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