The problem of the mental worker is to get sufficient physical
exercise to keep the mind and body at its maximum efficiency. This
problem gets more and more acute as he gets older. The amount of
work necessary to keep the man of sedentary habits in good
condition is about 100 to 150 foot-tons. Five hundred foot-tons is
the amount of work a soldier would perform by marching twenty miles
at three miles an hour on a level road.

It is a fallacy to think that sufficient exercise can be taken once
a week. In order to be efficient exercise must be regular and at
relatively short intervals. All exercise should tend toward using
all of the muscles of the body. In fatigue a person has lost
control over his muscles. The process of getting into condition,
therefore, is directed more toward strengthening the nervous system
in its control work over the muscles rather than in increasing
sheer muscular strength.

Pure creative mental work, although requiring no out-put of
physical energy, is perhaps the most productive of fatigue. The
brain gets more blood during physical activity and waste products
are much better removed. The effects of exercise are particularly
apparent in the lungs. More fresh air is brought to the lungs and
the waste products are driven off.

An attainable minimum for the average adult person might well
consist of taking simple exercises in his room, and to get out of
doors once a day and walk rapidly for at least half an hour. In
addition, it is desirable for any one up to fifty years of age to
take some kind of moderately violent exercise at least once a week.
This should be sufficiently strenuous to induce perspiration. This