TABLE 2.

Popular metaphors typically guiding theoretical predictions in the rest-break literature.

	Type	Metaphor and symbolic assumptions
1	Energetic-resource model	A hypothetical reservoir of resources is depleted through mental work (e.g., with time on task) and replenished during rest. The state of resource disposal is indicated by the decrease in performance speed in the task over time.
2	Strategic-resource model	Though resources are depleted during an ongoing sustained-attention task, they can be held in reserve or can be distributed in flexible ways. Thus, a straightforward relation of resource volume and performance over time is no longer assumed. Note: variants of strategic-resource models need further specification in order to be verifiable.
3	Ego depletion	Acts of self-control deplete resources and might potentially be replenished through periods of rest. The typical experimental arrangement goes as follows: Resources are depleted in task A and tested in a subsequent task B. In this way, ego depletion is concerned with the sequential transferability of a depleted across two subsequent tasks.
4	Satiation model	The critical variable relevant to performance is not a hypothetical volume of resources but the level of accumulated satiation that is experienced as aversive, thus considered the main driving force of behavior. Perceived satiation increases during repetitive work and dissipates during rest.
5	Reactive inhibition (Rasch model for speed tests)	Processing repetitive tasks yield a resistance gradient against further continuing with the ongoing action, conceived of as a distraction tendency. The inhibition gradient increases with prolonged task processing and leads to distraction (enforced rest) when reaching a critical threshold. This inhibition tendency thus increases monotonically during task processing and decreases during periods of (a) distraction or during (b) rest breaks.
6	Opportunity Costs	The term opportunity costs refers to the potential loss of a missed opportunity as a result of choosing one opportunity and foregoing another. These costs are indicated by the subjective experience of effort or aversion when proceeding with the ongoing task, but are relieved when the task is changed (that is, when alternatives are considered).
7	Attention Restoration Theory (ART)	Resources are claimed during the working hours of a day and replenished in the remaining free time and on weekends. Crucial is that recovery is not merely a function of time but depends on the context where rest takes place. Spending time in nature is assumed to be more beneficial than spending time in urban environments. In a strict way, ART is a psycho-sociological model but often misconstrued in the empirical literature.
8	Conservation of Resources Theory (CRT)	This is a psycho-hygienic model of stress prevention which is popular in the applied fields of rest-break research. In brief, the theory deals with how people perceive and estimate own resources including the costs of handling anticipated threats and challenges imposed by impending future events, and how people deal with uncertainty, respectively.

The models 1–3 employ a metaphor (resource volume) with a preconditioning parameter while the models 4–6 (satiation) make use of a delimiting parameter (thus both symbolic classes utilize a diametrically opposing metaphor to each other), though both metaphors make similar predictions. The models 7–8 are, in a strict sense, not performance models but theories about human wellbeing in the context of strain and recovery, though frequently referred to also by the experimental literature on mental fatigue and its recovery by rest breaks.