Fatigue and haste deplete cognitive endurance

The authors conducted a meta-analysis of data from six different studies, which involved a total of 1,088 U.S. adults. For 8-14 days, participants reported their fatigue levels several times a day and completed a short task on their smartphone, the Symbol Search test. In it, it was necessary to quickly determine which of the pairs of characters matched the pattern at the top of the screen. Reaction time served as an indicator of the speed of information processing, that is, how quickly a person perceives data and reacts to it.

Scientists examined how fatigue and the speed of task completion change from measurement to measurement and whether the level of fatigue or unusually high speed at one stage can predict a closer relationship between fatigue and slowing down at the next stage. The main indicator they were interested in was “the ability to ignore fatigue” (fatigue override): how well a person can maintain their work pace despite being tired.

The results showed a pattern that the authors compare to a marathon. If a runner feels severe fatigue or runs faster than usual at the beginning of the race, it becomes harder for them to ignore the fatigue and maintain their pace later on. Similarly, in the cognitive sphere: both greater-than-usual fatigue and unusually rapid information processing at one stage predicted that in the following hours, the link between fatigue and a decline in work speed would become stronger. That is, the ability to overcome fatigue declined.

At the same time, increased fatigue itself was associated with a slight decline in performance on the speed test. However, the predictive effect turned out to be more important: if a person felt particularly tired or worked faster than usual, this served as a signal that later it would be harder for them to maintain productivity amid fatigue.

According to the first author of the study, Raymond Hernandez, these data suggest the possibility of practical application: just as runners adjust their pace depending on how they feel, people could use their current sensations and work pace to decide when to take on complex tasks and when it would be better to take a break. However, this is still just a hypothesis: it needs to be verified whether this approach actually helps maintain cognitive productivity in real‑life situations, for example, during an important meeting or when dealing with complex instructions.

In the future, experts plan to conduct a more in‑depth study of the factors that influence the ability to maintain mental performance when fatigued. In the long term, this could help develop strategies to support productivity under conditions of fatigue.