818 THE POPULAR SCIENCE MONTHLY. 



of a series of partial efforts which are evolved at once in the arm 

 and shoulder, the vertebral column and the thighs ; and the stroke 

 of the racket in itself does not represent the whole expenditure 

 of force occasioned by the game. To it should be joined the mo- 

 tions preceding it and preparatory to it, or the player's changes of 

 attitude. All those who have held the racket know how rapidly 

 these motions have to be made. In less than a tenth of a second 

 one must look ahead and up to catch the ball on the fly, or stoop 

 to take it on the bound, or bend to one side to hit it a back stroke. 

 In these rapid changes of attitude the center of gravity of the 

 body is abruptly displaced, and equilibrium can not be preserved 

 without bringing a large number of muscles into energetic play. 

 The muscles of the thorax, the loins, and the pelvis contract and 

 bring the bony parts forming the framework of the body into 

 close action upon one another. The lower limbs, without leaving 

 the ground, also furnish a considerable interior labor, the pur- 

 pose of which is to assure the player a solid footing, a stability 

 essential to the force of the racket-stroke ; and even the feet seem 

 to fasten themselves to the ground, with the assistance of the 

 toes. 



Thus, in the game of tennis, the exercise is distributed among 

 a large number of muscles, and this fact enables us to explain 

 how the effects of work may be very much accentuated without 

 our being conscious of having made great efforts. In giving 

 racket-strokes we make infinitely less efforts than in raising heavy 

 chest-weights, yet we do not perform less work in a game of tennis 

 than in a practice of gymnastic athletics. 



In all natural movements we use a large number of muscles at 

 once, and we sometimes bring into action those which are very 

 remote from the point where the work appears to be localized. 

 Active games constantly tend to the division of the work among a 

 large number of muscles. This is the consequence of their very 

 character of natural exercises. Being copied from instinctive acts 

 of which they are simply the methodical regulation, they all pre- 

 sent the same character of causing the human machine to execute 

 much work without demanding much effort from it. The opera- 

 tion of the motions adopted by gymnastics proper is different. 

 That does not tend, in general, to seek out the associations of 

 muscles, called in physiology synergies, but rather to avoid them, 

 with the view of augmenting the effort of the muscles that are 

 brought into play by suppressing the co-operation of the other 

 muscles. 



The property of games is, then, to cause the production in the 

 human body of much work without great effort. Now, the hy- 

 gienic quality of exercise is not effort, but rather work. The 

 more work we do, the more we stimulate the great vital functions, 



