On the Efficiency of Muscular Work. 



213 



being done nor is energy expended in maintaining potential, which would 

 be the case, for instance, when standing erect. 



In conclusion, I note certain physiological factors which, coming into play 

 at the commencement of muscular work, can hardly increase in intensity 

 pari passu with the output of work, but increase the loss of heat, and 

 therefore depress the apparent efficiency. 



The first is the circulatory readjustment, leading to an enhanced flow of 

 blood through the muscles. Evidently this partial diversion of the stream 

 through the viscera has an upper limit which may be reached at a compara- 

 tively low rate of muscular output. No measurements suitable for the 

 present inquiry have been made. 



A second factor is the loss of heat due to air currents. In such work as 

 that on a bicycle ergometer, currents of some magnitude will be set up by 

 the rotatory movements of the legs. Hill, Griffith and Flack* concluded that 

 the total heat loss from the surface of a wet katathermometer was repre- 

 sented by : — 



H = (rt + & VV2) T + (c + (ml-') (F -ffl-' 



where V is the velocity of air movement, while T, a, b, c, cl, F and / are inde- 

 pendent of V. The movement factor might help to explain the rise of heat 

 production associated with a rotation of the pedals of the l)icycle ergometer 

 by the motor, the subject performing no work, as compared with the man's 

 heat production while sitting still on the machine. 



Benedict and Cathcart observed outputs of from 2-22 calories per minute 

 to 4-61 (rates of rotation from 58 to 104) under these conditions. The range 

 for sitting still was from 1"35 to 1-82. This cannot, however, be the whole 

 explanation. The rate of heat loss due to this cause must diminish with V, 

 since, from Hill, Griffith and Flack's equation we have dK/dV = k/Y^, 

 where k is a constant, while Benedict and Cathcart's data show that the rate 

 of increase of heat loss is greater between 86 and 96 revolutions per minute 

 than between 60 and 86. The observations are not, however, very 

 numerous, and I hope to be able to submit in a subsequent paper further 

 experimental results dealing with the point. 



The results which emerge from the study here published and seem to me 

 interesting are : — 



(1) Within fairly wide ranges, simple formulie of linear regression describe 

 the relations subsisting between heat production, body mass and work per- 

 formance with an accuracy sufficient for such purposes as roughly computing 

 the energetic needs of workers, doing the kind of work studied. As, 

 however, this work is of a specially simple kind, the type of calculation is 

 * ' Plul. Trans.,' B, vol. 207, pp. 183-220 (1916). 



VOL. XC. — B. S 



