One day as you climb a hill you suddenly feel your heart. A nagging chest pain accompanies your walk. When resting, it vanishes, yet when resuming it returns. "You got Angina, my friend", says your doctor, "get these pills, and carry on." He does not even bother whether WOB likes them or not. Chest pain is a message from WOB that your coronary vessels have narrowed and that f blood and oxygen supply to heart muscle declined. The heart gets weaker (its tolerance declines), pumps less blood to organs. Lacking oxygen they also suffer. Concerned about declining tolerance of organs, WOB send you a pain signal urging you to stop climbing.
You love walking, since it is healthy, take a pain killer, and up you go. WOB does not give up, and makes you feel dizzy and nauseous. You turn to the pharmacy, swallow two more pills and rush to enjoy the good weather. Now WOB is forced to make you faint.
The week in bed solved WOB 's concern. Organs get their adequate oxygen supply. You get out, and up to the hill. The chest pain is back. You reach into the pocket for the pills that you got from your doctor, and muse for a while. You remember the trip to the Andes, and wonder, why won't WOB increase oxygen throughput as it did then?- Why should it? It does not mind if you stop climbing hills, as long as all organs remain happy. How to convince WOB that hill climbing is important to you? Since whenever you climb it will object. In order not to annoy it, try climbing small hills that won't induce chest pain. WOB will than have to accumulate resources for maintaining tolerance when you climb small hills. In other words find ways to force WOB to accumulate resources, without its objecting. You start with small hills and in coming weeks gradually increase the effort. Always stopping short of chest pain. You may even end up participating in a Marathon contest.
Minor oxygen shortage that organs experience when you climb small hills, is essential to make WOB increase throughput. It is as essential as gravity to bone formation. You continue exercising, gradually increasing effort. WOB will supply the heart muscle with new vessels, and strengthen it. Other organs will also contribute to this effort. They also may grow new blood vessels, and utilize oxygen more efficiently. Moderate exercise boosts them all (process interleaving).
You look at the pills that your doctor gave you. They were intended to dilate your blood vessels, and so increase blood throughput. Which would let you climb your favorite hills. In the beginning, WOB might love this solution, since organs got their adequate oxygen supply. Yet the underlying process, arteriosclerosis, continued. Narrowing your vessels more and more, until even strong pills become ineffective. Your doctor might attribute their failure to unexplained resistance, like in chemotherapy, or insulin treatment.
Chest pain is a warning that heart tolerance declined. You may either protect your heart and avoid hill climbing, or boost your tolerance, by moderate exercise