The answer is called jumping gene hope this helps
Their surface area-to-volume ratio.
Cells are so small so the surface area and volume of them can be proportional to each other. This helps with the efficiency of the cell's absorption and waste expulsion processes. Also by the cell's smallness, communication from the nucleus to other organelles is fast and the cell can be regulated while the conditions for diffusion are still ideal.
During Stage A the muscles and tendons are working in unison to pull the leg backward and upward. In Stage B the tendons are being stretched and the muscles in the leg are driving forward, releasing their pent up energy (the muscles will burn oxygen until they run out at which point they will start producing lactic acid to keep providing energy for the leg, which is why your muscles burn when they are tired)