THE MUSCULAR SYSTEM 



253 



f 



Second class lever 



therefore, cannot move far- 

 ther than the power in this 

 lever. It must always move 

 a shorter distance. While 



such a lever is of great ad- f ,/.--' Jjp- 



vantage in lifting heavy p , 



weights outside of the body, \ 



it cannot be used f or increas- J IG ' "7- -Weight lifting levers. 



- , Diagrams show relative distances 



mg the motion of the mus- moved by the power and weight in 



cles. For this reason no well- levers having the weight nearer the 



defined levers of the second fulcrum than is the power. F. Ful- 

 classarepresentinthebody. 1 crum ' P ' p ' Power ' w > w '- Wei e ht - 

 Loss of Muscular Force. Using a small spring balance 

 for measuring the power, a light stick for a lever, and 

 a small piece of metal for a weight, 

 and arranging these to represent 

 some lever " of the body (as the 



1 The foot in lifting the body on tiptoe appears 

 at first thought to be a lever of the second class, 

 the body being the weight and the toe serving as 

 the 'fulcrum. However, if the distance which the 

 body is raised is compared with the distance which 

 the muscle shortens, it is found that the supposed 

 weight has moved farther than the power (Fig. 

 118). It will also be noted that the muscle which 

 furnishes the power is attached at its upper end to 

 the "weight." These facts show clearly that we 

 are not here dealing with a lever of the second 

 FIG. 1 1 8. Diagram of c ] ass The foot in this instance acts as a lever of 

 the foot lever. F. Fulcrum the first class with the fulcrum at the ankle joint 

 at ankle joint. W. Body and the toe pressing against the earth, which is the 

 weight expressed as pres- actual weight. Since the earth is immovable, the 

 sure against the earth, body is lifted or pushed upward, somewhat as a 

 While the muscle power fulcrum support is made to move when it is too 



Knee joint 



acts through the distance ab, 



weak to hold up the weight that is being lifted. 



In other words, we have the same lever action in 

 the fulcrum support (body) 



rr v * ' the foot in lifting the body as we have when one 

 is forced through the dis- ]ies face downward> and> bending the knee, lifts 

 tance rh. some object on the toes. 



