54 



PHYSIOLOGY 



CHAP. 



diminishing heights of contraction which is followed by the 

 constant phase with uniform values (Figs. 33 and 34). 



If the falling portion of the ergogram is obtained with a 

 sub-maximal load, the tracing passes into the constant phase 

 without altering the weight, in which case each contraction 

 represents a sub-maximal yield of work (Fig. 35). 



The level of constant work may be maintained for several hours 

 without any sign of the characteristic modifications of fatigue 



Fif;. 35. Ergogram of gastrocnemius showing decreasing and constant phase, at a 

 sub-maximal load. (Treves.) 



(Fig. 36), but finally there comes a moment at which the muscle can 

 no longer yield any mechanical work owing to the gradual onset of 

 rigor. 



In the ergogram of the gastrocnemius obtained with electrical 

 stimulation and an initial maximal load, the curve of the contraction 

 heights sinks rapidly to zero, or to a very low level, because after 

 a certain number of contractions the load becomes super-maximal. 

 If the weight could be gradually adjusted as the muscle weakens 

 so as to be maximal at each fresh contraction, the ergogram would 

 show no intervening stage of complete or almost complete cessation 

 of work, which is solely due to imperfect mechanical conditions. 

 A more important curve would stand out as a whole namely the 



Fio. 36. Ergograph tracing of rabbit's gastrocnemins (phase of constant work) after two hours' 

 rhythmical maximal excitation. (Treves.) The tracing shows a slight irregularity of the base 

 line of the contractions, but the work remains fairly constant. 



work curve, represented by a series of rhythmical contractions 

 executed under conditions of maximal work. Treves endeavoured 

 to approximate to such conditions in his experiments, and con- 

 structed a diagrammatic work curve} the course of which recalls 

 the form of a muscle twitch, with an ascending and a descending 

 phase, passing gradually into the period of constant work. 



Treves was the first to apply these methods of research to the 

 human subject. He did away with the support of the ergograph 

 lever, and made the subject lift a weight of 4-5-6 kgrms. (accord- 

 ing to the individual) every two seconds by a voluntary maximal 

 effort. In consequence the constant level was always obtained on 



