THE PHYSIOLOGY OF MUSCULAR WORK 245 



ficial. The chemical changes associated with muscular work are 

 probably facilitated by a temperature a degree or two above the 

 temperature during complete rest, and it may be that the dilatation 

 of the blood vessels of the skin relieves the heart from too great a 

 blood pressure. Most men find that they can work more com- 

 fortably and efficiently when they have " warmed up " to the 

 work, and some maintain that they work better when they begin 

 to sweat. The first half mile of a walk is not so well performed as 

 the later portions. Such evidence, however, would not justify a 

 statement that the improvement is solely due to a rise of tem- 

 perature, for there are other factors to consider. Among these 

 should be mentioned the adjustment of the heart and respiration, 

 the increased flow of blood through the muscles, and probably an 

 increased secretion of synovial fluid in the joints. This much, 

 however, may be said. Muscular work both in the case of man 

 and other warm-blooded animals is constantly accompanied by a 

 rise in the internal temperature ; the time of activity coincides 

 with the rise in the daily variation of temperature, the time of 

 rest and sleep with the fall to the minimum. Moreover, the daily 

 variation in temperature is accompanied by corresponding changes 

 in the pulse and the respiratory exchange. 



The following table will show the effect of various forms of 

 exercise upon the temperature of man : 



