On the Efficiency of Muscular Work. 



205 



work of a metal filer in an 8-^ hours' day to be 61,600 kilogramme-metres ; 

 that of a smith as rather more than twice as much. Taking these quantities 

 as equivalent to a medium and a heavy day's work, it will be interesting to 

 compute from equation (6) the requisite energy requirements of a man 

 weighing 67 kgrm. Taking the round numbers 60,000 and 120,000 

 kilogramme-metres, and reducing to thermal equivalents, we reach 3049 

 calories for the medium and 3929 calories for the heavy work. 



These figures are not very different from the usual standards. So far I 

 have merely examined the data from the same standpoint as that of 

 Glazebrook and Dye, viz., that of finding a formula which shall summarise 

 particular experimental data, and it appears that this comparatively humble 

 task can be readily accomplished, i.e., we can, with very little arithmetical 

 work, construct interpolation formulae which reproduce the observations 

 sufficiently well for the formulae to be used to approximate to intermediate 

 values within the range of the data. It is, however, more than doubtful 

 whether such formulae throw light upon the efficiency of the body as an 

 energy transformer when this term is strictly used, and I now propose to 

 examine the fundamental problem, 



The customary method of determining the efficiency of the human body as 

 a machine, prior to the publication of Macdonald's paper, was to subtract from 

 the total heat production associated with the performance of a measured 

 amoimt of external work the heat production of the same subject when " at 

 rest " ; the heat equivalent of the work divided by this has been termed the 

 " net efficiency," the " gross efficiency " being the quotient of work by total 

 heat production. Clearly the " net efficiency " will vary with the base line 

 chosen, i.e., whether "at rest" is taken to be lying on a couch, sitting still on 

 the ergometer, rotating its pedals without load, etc. Benedict and Cathcart* 

 discuss the choice of base line at length in their admirable monograph, and 

 point out the inconvenient diversity of base lines used or proposed. But 

 even these writers do not remark that the method is fundamentally open 

 to attack. Thus, if heat transformed be a function of work, the proper 

 measure of extrinsic efficiency would seem to be the reciprocal of the first 

 derivative of H with respect to W, the limiting value of the incremental 

 change of heat with work. This measure will differ considerably in value 

 from the " net efficiency " and may even lead to a different interpretation of 

 the results. For instance, Benedict and Cathcartf note a tendency towards 

 an increase in both gross and net efficiencies with increasing loads. With 



* Benedict and Cathcart, ' Muscular Work : a Metabolic Study, with Special 

 Reference to the Efficiency of the Human Body as a Machine,' Washington, 1913. 

 t Op. cit., p. 125. 



VOL. XC. — B. K 



