Physical Exercise 7 1 



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, typewriters, telegraphers, 

 and writers occasionally suffer from permanent contractions 

 of certain muscles of the arm, known as writer's cramp. 



101. 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, f but a time soon comes when no possible 

 effort will enable us 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 

 muscle will contract again. In brief, the functional power 

 of a muscle has a definite limit, and in fatigue that limit is 

 reached. 



102. Results of Muscular Fatigue. 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 spe- 

 cial effort of the will, the question of nerve exhaustion is 

 largely concerned. 



Thus, the incessant movements in St. Vitus' dance 

 result in comparatively little fatigue, because there is no 

 association of the brain with the muscular / action. If a 

 strong man should attempt to perform voluntarily the 

 same movements, he would soon have to rest. None of 

 the movements which are performed independently of the 

 will, as the heart beats and breathing movements, ever 

 involve the sensation of fatigue. 



