174 SECTIONAL ADDRESSES. 



is a definite variation in the course of the day in the capacity to carry 

 out work; that, in other words, a diurnal rhythm exists. There is a 

 certain amount of evidence also in favour of the view that a seasonal 

 rhythm exists. As Wilson has put it, 'It is tempting to suppose that 

 human performance may be dependent on a number of superimposed 

 rhythms corresponding with the periods of work, beginning perhaps 

 with the rhythm of the actual movement and ending with a seasonal 

 rhythm.' 



Further, when efficiency is measured in terms of output it is found 

 that there is a definite rhythm in output during the course of the work- 

 ing day and of the working week. It is well known that it takes an 

 appreciable time each day to work up to full power, and this is shown 

 distinctly in the daily output curve, which rises and then drops sharply 

 at the end of the work period. This type of curve is not peculiar to 

 any one industry. The rise is almost certainly due to the ' limbering 

 up,' and it is probable that the fall towards the end is largely due to 

 voluntary slowing. The total weekly output curve with the low 

 Monday effect and the sharp fall on Saturday resembles in general 

 shape the daily output curve. The main point about these curves is 

 that they seem to demonstrate the absence of progressive fatigue from 

 overwork, which would have been deduced had there been a sharp rise 

 at the commencement of the week, followed by a steady fall. 



The third of the potent factors in the control of fatigue is rest. If 

 work is done, rest is ultimately imperative. Rest not merely relaxes 

 the muscles, allowing a more thorough and complete removal of the 

 waste products and a more abundant supply of oxygen, but it removes 

 the strain of attention. Eest is best obtained not by simple quiescence 

 but by change of posture ; slow movement of another type to that which 

 produced the fatigue will, unless the organism is tired practically to 

 complete exhaustion, give the most beneficial results. It is common 

 knowledge that when the attention is concentrated, when our interest, 

 either in the work or in something cognate or even foreign to it, is 

 thoroughly aroused, spells of work or intensity of effort in its perform- 

 ance may be borne which under other circumstances might tax our 

 resources to the last degree. 



Forced work, i.e. work carried out at a pace other than that of the 

 performer's own selection, is much more exhausting and destructive 

 than where the subject is permitted to work at a rate of his own 

 selection. Laulanie, assuming that fatigue had a purely physical 

 origin, went the length of maintaining that muscles spontaneously find 

 the optimum rate of work where the intervals of repose exactly suffice 

 for sufficient recuperation, so that long spells of work may be done. 

 Such a conclusion does gain a certain amount of support from the 

 consideration, for example, of the cardiac cycle. 



So far, little attention has been paid to the duration of the rest 

 period in relation to the work done. As a general rule, it may be said that, 

 in the majority of occupations, although the hours of labour are con- 

 tinuous, the actual spells of hard manual work are discontinuous, either 

 due to the fact that certain operations are iiiteiinittent in their sevei'ity, 



