When you are working at your daytime job, using a computer, your human biological systems require that you deal with the development of three kinds of cognitive (mental) fatigue: acute, cumulative and task-specific. Performetric monitors the combined, additive effects of these three types of cognitive fatigue.

Acute cognitive fatigue builds up normally and unavoidably within one waking period of about 16 hours. It is happening to you as you read this post. Recovery from acute fatigue occurs as the result of one good-quality, nighttime sleep period of about eight hours.

Cumulative cognitive fatigue builds up across major waking periods when there is inadequate recovery (due to inadequate nighttime sleep) between waking periods. Recovery from cumulative fatigue cannot be accomplished in one good-quality, nighttime sleep period. It requires extra sleep, beyond about eight hours, on several sequential nights. The main contributor to cumulative fatigue is sleep debt.

Our understanding of task-specific fatigue has its roots in the study of physical work and acute muscle fatigue: repeated, demanding muscular work causes muscle fatigue and the need for recovery. Some argue that task-specific cognitive fatigue is actually habituation to a task and is not truly fatigue. Others may argue that a task is simply boring, and that this is not fatigue. Whatever it is called, the fact is that task performance declines as time performing the task continues.

Work generally places demands upon specific, fine-motor and visual functions. Some of the work requires vigilance, and some requires repetitive operations. Thus, we observe task-specific fine-motor muscular fatigue, visual fatigue, vigilance failures, monotony, and repetitive-stress injuries in the workplace. Each of these problems requires task-specific short-term and long-term fatigue management and recovery considerations.

If the individual cannot change tasks, then the effects of task-specific fatigue may be difficult to avoid; they may only be recognized and managed. Ideally, the manager should provide “a meaningful variety or mix of tasks so as to avoid boredom and performance decrement” (Murphy, Krusemark, & Moyer, 1968).