FATIGUE 63 



to weakness, imperfect development and nervous break- 

 down which is so commonly observed to-day. 



Disadvantages of work. The disadvantage of work 

 is that it may be so monotonous and prolonged as to cause 

 exhaustion of muscles and nerves. Overwork during 

 the growing period is especially harmful because it 

 interferes seriously with both the strength of the mus- 

 cles and their control by the nerves. It is especially 

 important that this should be considered in the training 

 for such games as football and baseball, where exhaustion 

 and heart strain are not uncommon. 



Fatigue, Since muscular activity is based upon the 

 combustion of food materials in the muscles, the ex- 

 haustion of these materials or the accumulation of waste 

 products results in fatigue and weakness. In order that 

 the muscles may be able to work for a long time, there- 

 fore, the rate of work must be such as to permit the 

 food supply to be renewed and the waste to be cleared 

 away. Even under these conditions, however, a limit is 

 set to the working time of the muscles by the fatigue 

 of the nervous system, which is often shown by the 

 person 's inability to keep his attention upon his work. 



Rest. Periods of rest are therefore essential to whole- 

 some work. This is especially true during the growing 

 period when exhaustion of the muscles and nerves leads 

 to their imperfect or unbalanced development. It -has 

 been found that a single small muscle may be so com- 

 pletely exhausted by hard work that it will no longer 

 contract, and yet after two hours of complete rest it 

 will be as strong as ever. If large groups of muscles are 

 exhausted in this way, however, their recovery from 

 fatigue is much slower. This is apparently due to the 

 much greater quantity of food materials oxidized and 

 of waste products produced. When the waste products 



