September 30, 1922] 



NA TURE 



455 



at the rate of 90 and 124 revolutions per minute re- 

 spectively, with the lower speed the net efficiency was 

 22-6 per cent., whereas with the higher speed it fell 

 to 15-7 per cent. Or again, with effective work of 1-58 

 calories at 71 and 108 revolutions per minute, the 

 efficiency was 24-5 per cent, and 15*6 per cent, respect- 

 ively ; and finally, with effective work of 1-35 calories 

 at speeds of 71. 94. and 105, the efficiencies were 23-1, 

 20-4, and 17-0 per cent. 



A. V. Hill has also recently dealt with this problem 

 in a most interesting piece of work, where the activity 

 was strictly confined to the biceps and the brachialis 

 amicus. He demonstrated very clearly that, in spite 

 of the fact that the slower the contraction the greater 

 was the amount of work done, all the advantage thus 

 gained was rapidly neutralised and dissipated as the 

 result of the slow contraction necessarily causing an 

 increased degradation of energy in the way of physio- 

 logical changes resulting from the maintenance of 

 contraction. It thus followed that a slow contraction, 

 powerful though it might be, was not necessarily one 

 of high efficiency. Hill found that the maximum 

 efficiency was very rapidly attained, the optimum for 

 the muscles investigated being apparently just less than 

 one second, but the fall which followed, as the duration 

 of the contraction increased, was a comparatively 

 slow one. On account, therefore, of the blunt nature 

 of the curve, the efficiency remained more or less 

 constant over a wide range of speeds. 



The load has obviously a direct connexion with the 

 speed at which work is done, but it has also a relation 

 to efficiency. Benedict and I found, for example, 

 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 carried out, maintenance or physiological 

 requirements which have to be covered form a large 

 proportion of the total energy output, a balance which 

 is steadily altered as the amount of external effective 

 work done increases. 



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 steadilv increasing load, the external work done 

 rose with decreasing 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 kilogram- 

 metre, 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 III. 



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 the 

 opinion that the severity of muscular work, qua 

 the organism as a whole, is a function of the static 

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

 to carry on, is more readily induced by static work 

 than by either positive or negative work. The follow- 

 ing figures, from experiments which I have carried out 

 with Miss Bedale and G. McCallum, show clearly this 

 diminution in efficiency as the static element in the 

 work is increased : 



Very closely allied with the rate of working is the 

 rhythm with which the work is performed. Although 

 they are not identical phenomena, they are so closely 

 related that the habit of work may be considered along 

 with rhythm. Every one is well aware that once a 

 rhythm, or the proper co-ordination in the play of a 

 set of muscles in the performance of some definite act, 

 is mastered, not only is the energy expenditure reduced 

 by the exclusion of numerous extraneous muscular 

 activities, but there is an actual enhancement of the 

 ease with which we perform the specified act. It is 

 not a mere question of rate. In a series of experiments 

 which I carried out with Burnett, the subject, working 

 on a specially geared ergometer, was allowed to select 

 his own rate of working, the load being varied from 

 nothing to 4 kilos. At each change of load the subject 

 was directed either to work rapidly or very slowly, 

 and after a period of such work was told to adopt the 

 rate he liked best. As the following table (Table V.) 



Resistance in kilos. 



Speed adopted, metres per sec. 



Work done, kilogrammetres per 



$ 1 'M. 



per kgm. 



812 S53 

 2-23] 2-25 



642 726 778 

 24+ 2-17 2-14 

 [204 22-9 23-3 



It will be noted that when the load becomes excessive 

 the efficiencv rapidly falls away. This means that, 

 although the effort may be continued 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, 



X11. 2761, VOL. I 10] 



shows, the rhythm of work was 

 7 o°g 0-24 o I5 i3 practically identical for all loads. 



This occurred under all conditions, 

 I l°l s°z 11° provided the working spells were 

 4 19-7 17-0 9-4 not f too long duration. If the 

 work were continued over a long period, the 

 rhythm tended to alter, to increase in speed, and if 

 the subject became really tired, periods of rapid move- 

 ment alternated with periods of slow movement. 



The rhythm adopted, although it may suit the 

 worker, is not of necessity the series of muscle move- 

 ments which lead to the least expenditure of energy. 



