LOCOMOTION 371 



diminishes the effects of the traction towards the base at the 

 moment of the impulsion and the horizontal speed of the body 

 at that instant, diminishes also, because it gives rise to a vertical 

 speed resulting from that impulsion. 



In jumping, the greater part of the work is done by the muscles 

 of the legs and shoulders. We therefore find that these muscles 

 are highly developed in athletes, who devote their attention to 

 jumping. The mass of the body is also an important factor, 

 since the height of the jump must necessarily be inversely pro- 

 portional to that mass. Also those with long legs can jump 

 higher than those with short ones? 



Calculations of the work done in jumping lead to very variable 

 results. 



The man is flung like a projectile with an initial speed v ; whence 

 the work done : 



then gravity performs work which the muscles can in no way 

 modify, except that they arrange the body so as to deaden the 

 shock. As a whole, the muscular work is difficult to estimate. 

 One can only get an approximate idea of it. For example, a 

 man weighing 65 kilogrammes leaves the ground at a speed of 8 

 metres per second, whence : 



r> K 



T i = i x 9^1 X 8 x 8 = 212 kilogrammetres. 



We must add to the above amount the work done in the pre- 

 paratory run necessary to give sufficient speed for the spring. 

 With this addition the total will be some 300 kilogrammetres. 



If the angle of the spring is 45 the space covered, at the above 

 speed, will be 6-52 metres ( 24). We have therefore to compare 

 6-52 X 65 = 424 metre-kilogrammes and 300 kilogrammetres, 

 which gives about -77 kgm. per metre-kilogramme. 



284. Climbing. In this method of progression the body is 

 pulled upwards by the arms, the elbows are more or less bent, 

 but most of the work is done by the powerful muscles of 

 shoulders and the back, and also by the larger pectoral muscles. 

 Man is far less favourably adapted for climbing than the anthro- 

 poids, especially the apes. The big toe is used to prevent the 

 body slipping back, as is particularly noticeable in the case of 

 savage races. 



Since the muscles of the arms are less powerful than those of 

 the legs climbing is a most fatiguing operation, and is indeed a 

 form of movement at variance with the anatomical and physio- 

 logical principles of the human body. 



