This section is from the "Health and Survival in the 21st Century" book, by Ross Horne.
That regular physical exercise conveys protection against disease is indicated by the fact that it makes people feel better, sleep better and tend to eat less, and by the fact that physically active people tend to live longer than the average. Not only that, but the records show that fit athletes in general suffer less from respiratory infections, breathing problems, diabetes, arthritis, multiple sclerosis, heart attacks, etc, and that the incidence of cancer among them is only one seventh of the average incidence.
These comparisons of athletes with non-athletes are applicable to people in the Western countries, where typically both athletes and non-athletes all consume the traditional foods of the, Western diet, so it is clear that the health protection provided by adequate physical exercise is gained by its effect of reducing lipotoxemia, the main underlying cause of all the diseases of the Western world.
The protective effect of sustained and reasonably vigorous exercise by people on the Western diet is multifold:
Thus the resultant improved condition of the blood and lymph fluid greatly enhance an improperly fed body's efforts to maintain homeostasis, with the consequent diminished likelihood of the diseases to which it would be otherwise susceptible.
However, exercise, while enhancing general circulation, does not prevent the build-up of atherosclerosis within the arteries and so a point is reached where exercise eventually becomes dangerous. Usually warning of this danger in the form of angina (chest pains) and breathlessness upon exertion occurs, but sometimes in an extremely fit person there is no early warning at all and a massive heart attack out of the blue is the only symptom they get. As previously explained, extremely fit athletes with blocked coronary arteries have such a development of small but numerous collateral vessels, that while blood viscosity is reasonable their heart muscles are still plentifully supplied with blood, but when the blood's viscosity for some reason becomes so high it cannot pass through the fine collaterals at all, suddenly the heart muscle is so deprived of blood that is stops.
The reason that this catastrophic event so often occurs after a period of strenuous exercise and not during the exercise is because the effect of sustained vigorous exercise is to greatly increase the number of platelets (clotting particles) in the blood, and this is a perfectly natural physiological event, but on top of blood viscosity already elevated by perhaps last night's wine and civilized dinner, the viscosity reaches disaster level. In this way many a confident sportsman has discovered physical fitness is no guarantee of long life.
Thus the role of physical exercise in protecting against the diseases of civilization is a real but limited one which works only to partially correct harmful factors which should not be there in the first place.
But even in the complete absence of the beforementioned harmful factors and in a state of perfect health, regular exercise, even light exercise, is highly desirable in order to ensure good lymph circulation not only to the muscles but throughout the entire body. The milieu interieur cannot remain pure if it becomes stagnant, so if someone is incapacitated and immobile it is important they be encouraged to move as much as possible, or massaged, to keep the lymph moving.