BOOK III. 

 HUMAN ENERGY. 



CHAPTER I. 



THE LAWS OF ENERGETIC EXPENDITURE. 



111. Generalities. From the point of view of utility, the 

 energetic expenditure of man is that which corresponds to 

 muscular activity only, but under certain circumstances, the 

 muscles remain contracted without performing any work, in 

 the mechanical sense of the word. The static effort thus 

 expended causes a consumption of energy, and can be regarded as 

 similiar to frictional work ( 60) or vibratory work ( 90). But the 

 contraction develops some force ; dynamically it has variable 

 degrees of speed and duration, its visible result being fatigue, which 

 is itself susceptible to variation. If, however, only the kinds of 

 activity which do not cause excessive fatigue are considered, then 

 without forcing the muscles, it will be possible to estimate the 

 amount of work according to the amount of energy expended. 

 The one will increase with the other. In the variations of the 

 expenditure will be seen the effect of the dynamic factors, force 

 and speed, when the work done remains constant. It will also be 

 seen how much the nature of the nutriment itself modifies the 

 value of the expenditure. 



On these lines the laws of the operation of the human machine 

 were formulated by Chauveau, who devoted about 20 years 

 to this study. His work is of great scientific value and practical 

 importance. It is our starting point in the study of physical 

 labour. 



112. The Laws of the Muscular Function ( l ) : Static Effort 

 Muscular contraction, whether periodical, as in work, or sustained 

 and of a vibratory nature, as in a static effort, is prepared for by 

 internal physiological work. Thus holding a dumbbell with the 

 arm stretched and immobile, or lifting it and lowering it several 

 times both necessitate an expenditure of energy. 



As to static effort, Chauveau verified the expression given 

 above ( 84). 



FP (1,+ r). 



which shows that for the same effort F, and the same time the 

 expenditure is : 



(*) See G. Weiss, Travail Musculaire et Chaleur Animals, 1909, Paris, 

 Masson. 



