The Activity.
The activity is affected by the amount of practice that one has had. It is affected by the extent to which the action has become a habit. It is affected by the degree with which one has got into the swing of the work. This may be an individual difference. Some workers find it possible to start at work at very much the pace that they will use when they are well into it. A large number of our records shows that most workers never get into the swing at the beginning of a work period. Not only the hour of the workday, but the time in the work period will have a strong effect upon the amount of work turned out. Again we have the question of spurt, when for some reason or other the activity is being performed at a pace that is above the normal pace. The effect of all these elements of the activity upon the fatigue itself depends upon the relation between mental fatigue and bodily fatigue. This relationship must be worked out by psychologists and physiologists. It is for the observer who measures fatigue in the industries to attempt to discover, as far as he can, what fatigue exists, and why it exists, and then to make both physical and mental conditions under which the activity is carried on as favorable to efficient activity as possible.