As normal human being, I started to felt 'mengantuk' or sleepy when after having a lunch..
This is because our stomach (specific to small intestine), need more oxygen to digest our food. Digesting system takes more our oxygen supply to our brain or our central nervous system. Digestion is the process of breaking down of chemicals in the body, into a form that can be absorbed. It is also the process by which the body breaks down chemicals into smaller components that can be absorbed by the blood stream.
In mammals like us, preparation for digestion begins with the cephalic phase in which saliva is produced in the mouth and digestive enzymes are produced in the stomach. Mechanical and chemical digestion begin in the mouth where food is chewed, and mixed with saliva to break down starches. The stomach continues to break food down mechanically and chemically through the churning of the stomach and mixing with enzymes. Absorption occurs in the stomach and gastrointestinal tract, and the process finishes with excretion.
So complicated to story here, because no body will understand enough by the end..
Finally, if we are fit enough, our lungs can absorb more and more (massive quantity) oxygen to supply through our body..so they can give enough supply to our stomach and brain at the same time. Working time need more speed and large effort. Training continuously will make we race faster and stronger. By the end we will found sports training will increase our work performance!
"need to do some muscle pumping to avoid sleepy after lunch..hahah"