166 MOVEMENT 



Practical Applications. — The data afforded by these 

 measurements may be put to practical use, for they 



performed in executing these movements obviously increases in pro- 

 portion to the degree of acceleration of the rate of step ; but a fact 

 which is at first surprising is that for the same number of steps per 

 minute a runner expends less energy than a pedestrian. Thus, at 

 ninety steps a minute, a man would expend in walking 1*4 kilogrmtrs 

 in the movement of the lower extremity, while a man in running 

 would only expend 0\5 kilogrmtrs. And yet the actual speed at which 

 the legs move in running is greater than in the former case. 



This difference is because the speed at which the limbs move in 

 reference to the body should be considered by itself in these esti- 

 mates. Now, the speed is greater in walking than in running. 



Indeed, for an equal number of steps per minute, the duration of 

 oscillation of the lower extremity is greater in proportion as the period 

 of contact of the foot is less. The period of contact in walking 

 occupies more than half the total time occupied in taking one step. 

 In running, on the contrary, the duration of contact is always less 

 than half, and as the angular displacement of the lower extremity is 

 practically equal in the two cases, it follows that the velocity of move- 

 ment of the legs will be less in running, because the period of oscilla- 

 tion will be of greater duration. A physiological result of this in- 

 equality in the duration of oscillation of the limb in different paces 

 is the intuitive tendency to begin running as soon as the rate of 

 walking becomes too fast. This is one of the numberless examples of 

 our natural instinct to expend the least possible effort in muscular 

 actions. 



B. Variation* in the Work don? hy the Vertical Oscillations of the 

 Body. — This factor in the work does not increase regularly with the 

 rapidity of footsteps. In walking, the work rapidly increases between 

 5.) and 70 steps per minute and then decreases. In running, it is very 

 geat when the number of steps per minute is small, and diminishes as 

 the rate becomes greater. This factor in the total work done depends 

 on the weight of the body and the amplitude of tie vertical oscillations. 

 The difference in the amount of work performed in various paces 

 bears a direct relationship to the amplitude of the above oscillations. 



Photographic and mechanical records of the vertical oscillations 

 show that in walking there is a relationship between the length of 

 stride and the amplitude of the vertical oscillations of the body, and 

 since we have proved that the length of stride increases with the 

 rapidity of the step up to 70 steps per minute, and then diminishes 

 rapidly as the step is further quickened, it naturally follows that the 

 work corresponding to these different steps varies in the same manner. 



In running, tne work done is greater when the rate of step is slow, 

 and then decreases indefinitely. The corresponding vertical oscilla- 

 tions vary in the same way. The body being suspended in the air 

 during part of the step in running is no longer constantly influenced 

 by the el anges in the directions taken by the limbs. Consequently, it 

 is the duration of the vertical oscillation which regulates the amplitude. 

 If the rate of step is slow, the body must be elevated very high so that 

 it may fall slowly on to the limb which comes in contact with the ground. 



