Breathlessness is, perhaps, the most common effect of undue exertion. Let
a middle-aged person, who is out of practice, run a certain distance, and
he is soon troubled with his breathing. The respirations become irregular,
and there is a sense of oppression in his chest. He pants, and his
strength gives out. His chest, and not his legs, has failed him. He is
said to be "out of breath." He might have practiced dumb-bells or rowed
for some time without inconvenience.

The heart is often overstrained, and at times has been ruptured during
violent exertion, as in lifting an immense weight. The various forms of
heart-disease are common with those whose occupations involve severe
muscular effort, as professional athletes and oarsmen. Haemorrhages of
various kinds, especially from the lungs, or rupture of blood-vessels in
the brain, are not uncommon results of over-exertion.

Excessive repetition of muscular movements may lead to permanent
contractions of the parts involved. Thus sailors, mechanics, and others
frequently develop a rigidity of the tendons of the hand which prevents
the full extension of the fingers. So stenographers, telegraphers and
writers occasionally suffer from permanent contractions of certain muscles
of the arm, known as writer's cramp, due to their excessive use. But the
accidents which now and then may result from severe physical exertion,
should discourage no one from securing the benefits which accrue from
moderate and reasonable exercise.

86. Muscular Fatigue. We all know how tiresome it is to hold the arm
outstretched horizontally even for a few moments. A single muscle, the
deltoid, in this case does most of the work. Even in a vigorous man, this
muscle can act no longer than four to six minutes before the arm drops
helpless. We may prolong the period by a strong effort of the will, but a
time soon comes when by no possible effort are we able to hold out the
arm. The muscle is said to be fatigued. It has by no means lost its
contractile power, for if we apply a strong electric stimulus to it, the
fatigue seems to disappear. Thus we see the functional power of a muscle
has a definite limit, and in fatigue that limit is reached.

[Illustration: Fig. 42.--A Well-Equipped Gymnasium. (From a photograph.)]

The strength of the muscle, its physical condition, the work it has done,
and the mental condition of the individual, all modify the state of
fatigue. In those difficult acts which involve a sp