IQO 



re;ports of investigations and projects. 



(3) Influence of muscular and mental work on metabolism and the efficiency of the 

 human body as a machine. Francis G. Benedict and Thorne M. Carpenter. 

 Bui. 208, Office of Exper. Sta., U. S. Dept. of Agriculture. 1909. 



The experiments on work were made with the respiration calorimeter, and 

 the subjects (bicycle-riders) performed large amounts of work on a station- 

 ary bicycle of peculiar construction, permitting the direct measurement of the 

 amount of muscular work applied to the pedals. There was measured, then, 

 simultaneously, the carbon-dioxide output, oxygen intake, heat output, and 

 the heat of external muscular work. The subjects ranged from men who 

 had no familiarity at all with bicycle riding, men who probably could not 

 have ridden a bicycle on the street without considerable effort, and a highly 

 trained professional bicycle-rider. The results are of interest in several ways, 

 but of perhaps the most special interest was the computation of the efficiency 

 of these men as machines. 



To determine the efficiency, the resting metabolism, expressed in calories 

 per hour, the calories produced per hour during work, and the number of 

 calories of external muscular work performed were measured. The effi- 

 ciency was computed by the formula £" = —7 , in which a represents the 



heat equivalent of the external muscular work, b the total heat output during 

 work, and c the heat output during rest. The results have been brought 

 together in table i. 



Table I. — Results of Experiments on Muscular Work. 



[Calories per hour.] 



Of special interest is the fact that the professional bicycler, N. B., and 

 the highly trained college athelete, J. C. W., on the one hand, and the wholly 

 untrained E. F. S. and A. L. L. on the other, had substantially the same 

 efficiency. While the professional bicycle-rider was able to do actually more 

 work per hour, the efficiency was not materially different. The results also 

 throw a most interesting light upon the influence of the load upon the efficiency 

 of man. In the experiments with N. B. there was an increasing series with 

 varying loads. Thus with an increased load resulting in an increased total 

 heat production above the resting metabolism of 19 calories per hour, there 

 was an increase in the work done amounting to 5 calories per hour. The 

 increase in load was accomplished by increasing the special electrical resist- 

 ances used in connection with the apparatus in that the current used to mag- 

 netize a powerful electric brake was increased. 



