176 THE HUMAN MOTOR 



before fatigue sets in, n contractions have taken place, the total 

 work during that period is nPh. Fig. 135 shows two of these 

 traces or ergograms. The traces of the contractions show a 

 decreasing amplitude and varying rhythm. The voluntary 

 muscular contraction lasts at least 6 to 7 hundredths of a 

 second, i.e., 1,000 contractions per minute approximately, but 

 this rhythm is impossible in practice, as has already been shown 



( !) 



The rhythm of the contractions brings about an interval of 

 repose necessary for the reparation of the muscles (see Fatigue, 

 ( 146). This is a fundamental fact, which explains why, in the 

 living machine, the movements are reciprocating, although in 

 the case of inanimate motion, rotary movements are the most 

 economical and regular. In rotation, it is not possible to realise 

 the indispensable organic reparation, nor to rid the cellular organs 

 of their waste. 



120. Ergograms have led to the following conclusions : Each 

 muscular group produces its maximum work for a definite value 

 of the load. If the latter is modified, the rhythm of the contrac- 

 tions must likewise be modified. Thus the rhythm being 6 per 

 minute, and the weight to be displaced being 3 kilogrammes, the 

 flexor muscles of the middle finger could work almost indefinitely. 



Double the weight and it will be necessary to double the 

 interval of repose. If the rest periods are increased fourfold 

 the preceding maximum of work done will be exceeded, but it 

 must be remembered that the duration of the repose, necessary 

 for the reparation of the muscle, increases more quickly than the 

 weight lifted. 



Instead of continuing the record until complete fatigue sets 

 in (the amplitude being then almost zero) the work is often 

 interrupted by a halt of a few minutes before fatigue sets in. For 

 instance ( 1 ), under a weight of 3 kilogrammes and with a rhythm 

 of 30 per minute, make 15 successive contractions and then rest 

 for half an hour. Then a day's work will give : 28-164 kgm. 

 (right middle finger) and 26-855 kgm. (left middle finger). But 

 fatigue would have appeared sooner if, pushing the ergogram 

 to its end, it had been followed by a rest even of two hours. The 

 daily work would only have been : 



13-674 kgm (right middle finger) ; 14-742 kgm. (left middle 

 finger). 



From the above will be seen that frequent short intervals of repose 

 are better than one long rest. 



(M A. Maggiora (Arch. Ital. Biol,, vol. xiii. f p. 210 ; 1890), 



