There are two ordinary things in a man’s life that make his heart beat faster.

-Walking up the stairs and
-Watching Pretty girls.

The former reaction is mainly due to physical exertion, while the latter one is due to psychological stress. Our interest here, however, is solely focused on psychological factors in the study of physical work, such as problems concerning subjective estimates of force perception, exertion, and fatigue.

Before studying the use of scaling methods in psychophysiological fatigue, it was felt necessary to know the concept of fatigue.

Physiologists often consider fatigue simply as a decrease in physical performance. Physiologists try to consider it a condition affecting the mental process, including factors such as fatigue, motivation, and the resulting deterioration of performance. Ergonomists and physicians lay stress on the consequences of fatigue.