In this case, we have our action potential generated. And then somewhere in between, we have the initiation of the muscle contraction. So this is because before the muscle contraction actually takes place, we have to increase the concentration of our calcium ions inside the cytoplasm of that cell. And that means we have to wait a little time period. We have to wait a little for that calcium concentration to actually build up. And what causes that build up of calcium ions is the action potential itself.