FACTORS INFLUENCING EFFICIENCY 395 



the adoption of other base lines in which movements which play 

 little or no part in the determination of the efficiency are elimi- 

 nated. As the main object is to determine the efficiency of the 

 body performing a definite act it has been suggested that the best 

 result will be obtained when the various activities associated with 

 the determination of the energy output both of the base line and 

 of work are more or less comparable, that is, where the extraneous 

 muscular motions incidental to riding with weight are common 

 to both determinations. Such a comparison is that obtained 

 when there is a change from a moderate to a heavy load. As 

 will be noted from the above summary of efficiencies the average 

 efficiency under these conditions is about 30 per cent. 



There is a certain amount of evidence available which would 

 suggest that the degree of efficiency obtained varies with the 

 groups of muscles used in performing the work. The efficiency 

 of muscles less commonly in use than the leg muscles is some- 

 what lower, flexor groups may differ from extensor groups, etc. 

 The state of training, too, probably influences, although apparently 

 not very markedly, the degree of efficiency. And finally, some 

 workers maintain that the efficiency may also be, to some extent, 

 dependent on the nature of the diet. Macdonald maintains that 

 the efficiency of muscular work is a function of body mass. 



Greenwood, who has carefully analysed the data obtained by 

 many of the workers, has come to the conclusion that although 

 as yet no law can be formulated connecting heat production 

 and work performance, within fairly wide ranges, simple formulae 

 of linear regression do describe the relations subsisting between 

 heat production, body mass and work performance, with an 

 accuracy sufficient for such purposes as roughly computing the 

 energetic needs of workers doing the kind of work studied. 



In addition to the above-mentioned factors which influence 

 efficiency there are certain others connected with the performance 

 of the work itself which apparently play a determining part. 

 These are load and speed. 



Although it might be presumed that load would exercise a 

 marked influence, such experimental work as exists tends to show 

 that increase of load within limits does not materially influence 

 the efficiency of the body. There is, however, a slight tendency 

 for the work to be done more efficiently when the load is changed 

 from a moderately heavy to a heavier one than when the change 

 is from a light to a heavy load. 



The influence of speed, that is the rate at which the work is 



