suitable and beneficial to another. Then the condition of the individual,
rather than the character of the muscular work, is always a most important
factor.

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. Hæmorrhages 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