You get tired when you run because our leg muscles don't get enough oxygen anymore.
That is known as fertilization
The respiratory system expels carbon dioxide
<span>As an action potential reaches a muscle cell, it triggers calcium to release from the sarcoplasmic reticulum of the cells. The calcium ions then flow into the cytoplasm and bind to the troponin and tropomyosin molecules in the actin filaments of the muscle cells.</span>
