THE NEUROMUSCULAR SYSTEM: FATIGUE 113 



may include the gain through coordination. This is what 

 we mean by acquiring skill. In all but the most elemen- 

 tary movements the best combinations of contractions 

 on the part of different muscles have to be secured by 

 practice. The physiologic change which makes the 

 gain possible must consist in the establishment of new 

 ties between the various groups of neurons at all levels 

 in the central nervous system. 



Better coordination means better economy of force. 

 When one is riding a bicycle in the early days of the ex- 

 perience much strength is wasted. The foot which is 

 coming up resists the foot which is going down. This is a 

 type of an interference which is widespread where many 

 muscles are set to work in an unwonted form of exercise. 

 When the "knack" is attained, much less internal work 

 is done for a given external result. This has been proved 

 by measurements of the respiratory exchange in persons 

 who were performing certain tasks (climbing hills, for in- 

 stance), with and without adequate training. It is alto- 

 gether probable that in reaching the full measure of 

 economy, precision, and endurance the cooperation of 

 the cerebellum is secured. 



