558 NUTRITION OF FARM ANIMALS 



Much study has been expended upon horizontal locomotion in 

 man. The somewhat extensive literature of the subject as sum- 

 marized by Benedict and Murschhauser l shows clearly a marked in- 

 crease in the net expenditure of energy per unit of locomotion as the 

 speed increases. Brezina and Reichel 2 found that beyond a certain 

 maximum speed (about 80 meters per minute) it became an exponen- 

 tial function of the velocity, while below that speed only slight varia- 

 tions were shown. 



The influence of speed upon the net efficiency in work of ascent 

 seems to be much less marked than that upon the expenditure in 

 locomotion. No results upon the horse are available. With man, 

 Brezina, Kolmer and Reichel 3 in experiments on a tread power found 

 that the net expenditure per kilogram and meter distance in walking 

 up a grade was substantially independent of speed at velocities con- 

 siderably below the maximum just indicated. Since this was found 

 to be true also of horizontal locomotion, it follows that the efficiency 

 in work of ascent must also have been nearly independent of the speed. 



Benedict and Cathcart 1 found that both the net and gross efficiency 

 in work done on their bicycle ergometer, which might be regarded as 

 a form of draft, decreased as the speed increased. In none of the 

 various experiments cited was there any air resistance, the work being 

 done on a stationary apparatus. In actual practice this is an im- 

 portant factor at high speeds, increasing very much more rapidly 

 than the speed. 



664. Influence of gait. According to Zuntz and Hage- 

 mann's results (656) an increase of speed in the horse obtained 

 by a change of gait from a walk to a trot involves a notable 

 increase in the net energy expended for locomotion per unit of 

 weight and distance, although an increase in the trotting speed 

 up to a moderate limit causes no further increase. With man, 

 on the contrary, Benedict and Murschhauser find that locomo- 

 tion at a given speed is performed more economically in running 

 than in walking. 



Such differences are doubtless brought about to a consider- 

 able extent by differences in the height to which the body 

 is lifted at each step and the degree to t which extraneous 

 motions, such as swinging the arms in rapid walking, are 

 brought into play. 



1 Carnegie Institution of Washington, Publication No. 231 (1915), pp. 12-28. 



2 Biochem. Ztschr., 63 (1914), 170. 



3 Biochem. Ztschr., 65 (1914), 16 and 35. 



4 Carnegie Institution of Washington, Publication No. 187 (1913), 138. 



