56 



MOTION AND LOCOMOTION 



Power exerted by the muscles. In walking, the 

 power required of the muscles is that which is necessary 

 to carry the weight of the body, which is borne en- 

 tirely by the muscles of the legs. When a hod-carrier 

 takes up a load of bricks, or the soldier his equipment, 

 the extra power demanded of the leg muscles amounts, 

 to not more than a quarter or a half of the regular work 

 of carrying the body 's weight. The arm and trunk mus- 



FIG. 47. Analysis of a single step in ordinary walking. (Bradford.) 



cles are able to do a larger amount of work in propor- 

 tion to their weight than the legs, since they do not 

 have to support the weight of the body as a whole. The 

 freedom of the arms for this work is made possible by 



as possible. It is, however, not difficult to convert oblique forces 

 into rectangular forces by the application of the principle that the 

 true lever length for use in a problem involving an oblique force, 

 is not the full length but is equivalent only to the shortest distance 

 between the fulcrum and the line of action of the weight and of 

 the power. 



