36 ENERGY TRANSFORMATIONS DURING HORIZONTAL WALKING. 



The detail of the bearings is given in figure 4, which shows the method 

 of support on the angle frame of the treadmill. The thick belt thus 

 rests upon a rolling, frictionless surface throughout the whole length of 

 the space over which the man is to walk, providing a substantial, 

 perfectly smooth path for the subject. It is impossible to feel the 

 numerous steel rolls, as the space between them is so small. The 

 leather belt gives a particularly satisfactory footing. The speed of the 

 motor may be modified at will and tests may be made at rates of speed 

 varying from less than 50 meters per minute, the equivalent of a very 

 slow walk, to 150 meters per minute, or a rapid walk, if not, indeed, 

 running. 



Since the driving of the treadmill belt is from the rear wheel, all tend- 

 ency to slip is at this point. Consequently, by counting the revolutions 

 of the forward wheel, where no slip can possibly take place, we have an 

 accurate measure of the total distance traveled. Upon the periphery 

 of the forward wheel are attached two revolution counters (one on 

 each side) 1 which can be read intermittently. One runs continuously; 

 the other may be connected or disconnected at will. In use, the 

 subject walks upon the treadmill for several minutes before the experi- 

 mental period commences. At the exact moment of beginning the 

 measurements of the respiratory exchange, one of the revolution 

 counters is put in action, so that the distance covered during the 

 period is accurately known. It is thus unnecessary to assume con- 

 stancy in the revolution of the motor or to apportion the distance 

 walked during the period from the total measurement of the revolutions 

 of the front wheel during the entire time the subject is walking. 



Considering the number of the various bearings and the size of the 

 apparatus it produces much less noise and vibration than any treadmill 

 that we have thus far seen. By means of adjusting screws at the for- 

 ward end of the treadmill, which are not shown in figure 3, any desired 

 elevation can be readily secured. In this research, however, the tread- 

 mill was invariably used in a perfectly level position. At the date of 

 writing (June 1915), after two years of use, the apparatus shows no 

 signs of wear and gives most satisfactory service. 



ACCESSORY APPARATUS. 



The universal respiration apparatus and the treadmill provide accu- 

 rate measurements of the total carbon-dioxide production and the 

 oxygen consumption and of the distance walked by the subject. In 

 addition to this, certain observations are important, particularly in 

 studying the physiology of walking, and it was therefore necessary to 

 have some means of recording accurately the respiration, the pulse, 

 the number of steps taken by the subject, and the height to which the 

 body was raised with each step. 



'But one of these (R) is shown in figure 3. 



