ISOTONIC CONTRACTIONS 



in 



There must, therefore, he a close correlation between tlie enerf>y 

 evolved and the oxygen intake. 11 we were to measure the amount 

 of oxygen used by a man resting and kept warm, and then found 

 the extra amount of oxygen he used when he did a measured 

 amount of work, we would fmd the cost of the work in oxygen. 

 Every gram of glucose requires 1-06 grams of oxygen to convert it 

 into CO2 and H2O, and. therefore, we could calculate the cost of 

 the work in glucose from the oxygen consumption, presuming that 

 only glucose was oxidised (Chap. III.). That is, the basis of 

 muscular activitt/ is oxidation, just as the basis of the activity of a 

 steam engine is the oxidation of coal. 



TABLE XXVI 



Gaseous Exchange in M. Levator Labii Superioris of the Horse per 

 GRAM OF Muscle per minute (Chauveau and Kaupmann) 



Heat Developed. Every one knows without the use of thermo- 

 meters or thermopiles that muscular action produces heat. The 

 employment of heat measuring devices applied to isolated muscles 

 or to man as a whole (calorimetric chambers) enables us to formu- 

 late equations relating the exact amount of heat generated to the 

 work done and to various other factors. For example, two of the 

 metabolites of muscular action, lactic acid and CO,, may be equated 

 with either the heat evolved or the tension developed in an isometric 

 contraction or with the work done in an isotonic contraction. As 

 during the cycle of muscular activity, lactic acid disappears at the 

 same time as COg appears, one might consider that the heat 

 developed came from the oxidation of the organic acid. In part, 

 this is the truth, but it is not the whole truth. Let us consider 

 briefly the various stages in the cycle of changes produced when 

 muscle does work. 



Muscular Cycle. The muscular cycle from resting state to the 

 return to the resting state is divided into four well-defined stages, 

 e.g., (1) initiation of contraction, (2) maintenance of contraction, 

 (3) relaxation, and (4) recovery or restitution. The three earlier 

 Components do not necessarily require the presence of oxygen. 



