I.— PHYSIOLOGY. 171 



Tlie load has obviously a direct connection with the speed at which 

 work is done, but it has also a relation to efficiency. Benedict and I 

 found, for instance, that both the gross and net efficiencies within the 

 limits of our experiments increased with the load. The probable 

 explanation of this result is that when light work is can'ied out, mainten- 

 ance or physiological requirements which have to be covered form a 

 large proportion of the total energy output, a balance which is steadily 

 altei-ed as the amount of external effective work done increases. Inci- 

 dentally, Hill drew attention to a most important factor in the con- 

 sideration of the efficiency of muscle, viz., the relation between the 

 maximal and the submaximal effort. Hill suggested that the less power- 

 ful effort was the result of the maximal contraction of only a poi'tion 

 of the muscle fibres, and that the fibres not directly involved in the 

 contraction changed passively, i.e. they were made to confoi-m to the 

 shape of their active neiglibours. This, of course, will automatically 

 lead to a considerable waste of energy in changing the form of the 

 muscle as a whole, therefore the submaximal effort will be less efficient 

 than a. maximal effort of the same duration in time, and further ' the 

 highest efficiency of a submaximal effort is obtained in a slower cor 

 traction than that of a maximal effort.' 



On the other hand, when the loads become excessive there is a 

 definite falling off, both in gross and net efficiencies. Laulanie, who 

 also investigated this question, found that at voluntarily selected speeds, 

 with steadily increasing load, the external work done rose with decreas- 

 ing speed until the load became excessive. He maintained that there 

 were two optima, (a) an economic optimum at 4 kilo, load with high 

 efficiency and a low oxygen consumption per kilogrammetre, and (b) a 

 mechanical optimum between 8 and 12 kilo, load when the output in 

 unit time was highest. The following table from Laulanie makes his 

 point clear: — 



Table IV. 



Resistance in kilos. .1 2 3 4 5 6 8 10 12 15 



Speed adopted, metres per 

 sec 1-49 1-07 0-80 0-61 0-54 0-44 0-37 0-29 0-24 0-13 



Work done, kilogram- 

 metres per 5 min. . 448 642 726 778 812 853 896 905 906 570 



Oxygen intake in c.e. per 

 kgm 3-5 2-44 217 2-14 2-23 2-25 2-43 2-53 312 5-31 



Efficiency per cent. . 14-1 20-4 22-9 23'3 22-3 22-1 20-4 19-7 17-0 9-4 



It will be noted that when the load becomes excessive the efficiency 

 rapidly falls away. This means that, althongh- the effort may be con- 

 tinued as strenuously as before, and although the physiological cost 

 of the effort remains at a very high level, the amount of external work 

 done is reduced to a very low figure. The static element in the muscular 

 effort has become dominant, and static expenditure is parasitic on 

 dynamic work. The more static the work becomes the greater is the 

 fall in the efficiency. Personally I am of tbe opinion that the severity 

 or hardness of muscular work, qva the organism as a whole, is a func- 

 tion of the static component of the effort made. Fatigue, i.e. inability 

 to cany on, is more readily induced by static work than by either 



