Tired now—or thinking faster? Both are linked to a harder time pushing through fatigue later

by Ingrid Fadelli, Medical Xpress

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edited by Sadie Harley, reviewed by Robert Egan

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Many people continue working, studying or completing everyday chores even when they feel tired and their energy is low. However, reliably completing tasks while fatigued can require considerable mental effort.

Researchers at the University of Southern California, Yeshiva University and other institutions recently carried out a study exploring whether feeling more tired than usual or performing faster than usual on a mental task predicted a reduced ability to maintain performance while tired in the following hours.

Their findings, published in Communications Psychology, suggest that feeling more tired and processing information faster than usual could be linked to a reduced capacity to push through fatigue later.

"If you imagine a person running a marathon where performance is speed, someone who already feels very tired at the beginning of the race might find it harder to ignore that fatigue to maintain their pace later in the race," Raymond Hernandez, first author of the paper, told Medical Xpress.

"If a runner runs faster than their usual pace at the beginning of a race, fatigue could be harder to ignore later in the race because more energy was used up. We wondered whether the same pattern might emerge as people tackle mental tasks throughout the day for their job or other responsibilities—a kind of cognitive marathon."

Tracking tiredness and processing speed in everyday settings

Hernandez and his colleagues analyzed the data collected as part of six different studies, which involved a total of 1,088 adults living in the U.S. The participants were asked to report their levels of fatigue and complete a short task several times each day, for a total of eight to 14 days.

The short task, called the Symbol Search task, required participants to quickly identify matching symbols on a screen. This assessed their processing speed, or how quickly they could take in information and respond to it.

"We examined whether fatigue and performance moved together from one assessment to the next, and whether a person's fatigue or speed at one assessment predicted a stronger relationship between the two at the following assessment," explained Hernandez.

"The principal investigators of the various studies came from a wide range of fields, but all shared an interest in fatigue and were even willing to help with the paper."

When they analyzed the data from the six studies, the researchers found that feeling more tired than usual was associated with slightly poorer performance on the processing speed task. Feeling more tired than usual and performing faster than usual each predicted a stronger link between fatigue and slower processing speed at the following assessment. This indicated a reduced ability to maintain performance despite fatigue in the subsequent hours (i.e., lower "fatigue override").

"The pattern resembled what we might expect in a running marathon: both feeling more fatigued and performing faster than usual were associated with a harder time overriding fatigue later on," said Hernandez.

Understanding the implications of pushing through fatigue

This study offers some hints about how fatigue and faster mental processing than usual relate to people's subsequent ability to maintain mental performance while tired. Future studies could explore the patterns observed by the researchers in greater depth, perhaps using a broader range of methods to measure fatigue and processing speed. They could also explore potential practical applications.

"Our results raise the possibility that, much as runners adjust their pace based on how they feel and how fast they are going, people could use their recent fatigue and performance to guide when they tackle demanding tasks or take breaks," said Hernandez.

"Whether that approach helps people sustain cognitive performance during meaningful daily activities—such as participating in an important meeting or following complex medication instructions—needs to be tested."

Hernandez and his colleagues are keen on continuing their exploration of factors that may shape people's ability to maintain cognitive performance when they feel fatigued. Eventually, their work could inform the development of strategies designed to support people's ability to maintain mental performance while tired.

Written for you by our author Ingrid Fadelli, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.

Publication details

Raymond Hernandez et al, Fatigue and processing speed predict subsequent fatigue override, evidence from a coordinated analysis of six EMA studies, Communications Psychology (2026). DOI: 10.1038/s44271-026-00537-1.

Journal information: Communications Psychology

Key medical concepts

Fatigue

Clinical categories

Sleep & RecoveryPsychology & Mental health Who's behind this story?

Ingrid Fadelli

Freelance journalist with BSc Psychology and MA International Journalism. Covers AI, robotics, neuroscience, and astrophysics since 2018. Full profile →

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries. Full profile →

Robert Egan

Bachelor's in mathematical biology, Master's in creative writing. Well-traveled with unique perspectives on science and language. Full profile →

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