FATIGUE AND RECOVERY OF MUSCLES AND NERVES 



445 



D show that exhaustion comes on more rapidly the smaller the interval between 

 contractions. In Fig. 181, A we find only fourteen contractions before complete 

 exhaustion, mechanical work = 0.912 kg. m. In Fig. 181, B the number of con- 

 tractions is eighteen, and the mechanical work done 1.080 kg. m. In Fig. 181, C 

 the number of contractions is thirty-one and the mechanical work 1.842 kg. m. 

 With a rhythm of one contraction every ten seconds no fatigue at all appears 

 (Fig. 181, D). An interval of ten seconds, therefore, is sufficient to permit a 

 skeletal muscle to recover completely. 



When a muscle is worked at a rapid rhythm to the point of complete exhaus- 

 tion, it requires a rather long time to recover completely in the experiments of 

 Maggiora from one and one-half to two hours. It was also shown in these 

 experiments that the last contractions of a series ending in complete exhaustion, 

 are the most fatiguing. If only the first part, say the first fifteen contractions, 



-MUM 



D 



FIG. 181. The onset of fatigue under stimuli of the same strength, given at different intervals, 

 after Maggiora. A, once a second; B, once every two seconds; C, once in four seconds; 

 D, once in ten seconds. To be read from right to left. . 



of a fatigue series be carried out and rest be then permitted, the muscle will 

 recover in a much shorter time proportionally than if it were completely fatigued. 

 Consequently the total amount of work which can be done in a day is consider- 

 ably greater if the muscles be not pushed at any time to the limit of their 

 powers. For example, a muscle making fifteen contractions every thirty min- 

 utes for fourteen hours did mechanical work of 26.9 kg. m. ; the same muscle 

 when made to perform the whole series of fatigue curves every two hours accom- 

 plished a mechanical work of only 14.7 kg. m. ; a difference of 12.2 kg. m. 



Anaemia, fasting, want of sleep, among other things, reduce the working 

 power, and favor the onset of fatigue. The capability of work is increased, on 

 the other hand, by rest, by taking food, and by massage the latter even in 

 case the muscle be previously not fatigued. The effect of massage after work 

 therefore consists not only in the removal of products arising from the expendi- 

 ture of energy, but also, and to a considerable extent, in the more active circu- 

 lation of the blood and lymph and possibly in some alteration of metabolism 



