Science Journalism Corner: How Your Brain Might Trick You During Endurance Activities

You creep behind the ferns and trees surrounding a small pond. A half-eaten hippopotamus carcass lies at the edge of the water. Carefully glancing for crocodiles, you approach the carcass, eager to finally feast after spending hours scrounging the dry woodlands for food. Using a stone scraper, you tear away the meat connected to the ribs and limb bones. The stone screeches as it digs into the bones’ outer layers, leaving cut marks. After satiating your hunger, you collect some extra meat for your camp, and begin the arduous process of navigating your way back—walking for hours while tracing your own tracks and keeping a watchful eye for other predators. 

Hopefully, the scene above is not too relatable, as it reflects the point of view of an early modern human living in northern Tanzania more than one million years ago. But it illustrates the mental and physical challenges our ancestors battled and poses a key question: what happens when you experience both simultaneously? 

Increased mental burden combined with an endurance exercise activity may make you fatigue more quickly. Why this happens is unclear, but a new study reveals an interesting dynamic: thinking hard while exercising may make a long workout feel tougher than it actually is. But there may be ways to mitigate this effect, evolved long ago in our hunter-gatherer ancestors.

The ability to combine endurance exercise with cognitive demands likely aided early modern humans’ survival. Starting from around two million years ago, our ancestors began roaming farther for their food: they took up lifestyles as hunter-gatherers who traveled far distances daily to bring food back to camp. Modern hunter-gatherers in the Kalahari desert can sometimes spend hours or days tracking down a single Kudu, traveling distances of up to 35 kilometers. Often, tracking requires immense mental effort. A prey animal may throw the hunters off by circling back on its previous path or rejoining a herd. If the hunt is successful, the hunters still need to navigate back to their main camp. As a result, hunting and gathering in challenging environments requires not only physical endurance, but also proficiency in certain cognitive skills. 

Nowadays, despite most people acquiring their food from grocery stores rather than hunting and gathering, some activities may still challenge both your mental and physical capabilities. Recreational hunting, ultra-marathons, or a 36-minute boxing match are just a few examples. Discovering how our ancestors were able to effectively acquire food, despite the increased cognitive burden that hunting and gathering imposes, may change how we think about improving physical endurance. To investigate this dynamic further, we need to understand how our bodies react to challenging mental stimulation while engaging in extended exercise. 

Scientists have previously demonstrated that mentally demanding tasks prior to endurance exercise can accelerate fatigue. But not much is known about how our bodies react to increased cognitive engagement during prolonged exercise. 

To solve this mystery, Daniel Aslan, a recent PhD out of the Human and Evolutionary Biology department at the University of Southern California, and his research team put 30 healthy adults through two sessions of treadmill walking: exercise-only and exercise-cognitive. Aslan’s team expected to find that combining cognitive demand with exercise leads to an increase in perceived effort. They also predicted that individuals with enhanced cognitive abilities in areas necessary for a hunting and gathering lifestyle would not experience the same effects. 

For the exercise-only session, the participants were instructed  to walk for thirty minutes or until they could no longer continue. For the exercise-cognitive session, the participants engaged in two problem-solving tasks while walking on the treadmill. The first was memory-based: random numbers appeared sequentially on a monitor, and participants were asked to signal whenever the current number matched the number that was displayed two numbers ago. During the second task, participants had to signal whenever a word for a certain color and the font color matched.   

To determine levels of fatigue, the researchers collected the participants’ rating of perceived exertion (RPE)—a number between 6 (no effort) and 20 (maximal effort)—that the participants provided every two minutes. However, to test their hypothesis that concentrating while exercising only increases perceived effort, the researchers needed to know how hard the participants were actually working. Taking measurements of oxygen inhaled and carbon dioxide exhaled allowed the researchers to determine how much energy the participants were really using compared to their RPE. 

During the exercise-cognitive session, the participants reported higher RPEs. Paradoxically, their actual energy expenditure during this condition was lower compared to the exercise-only session. For some reason, the participants thought they were working harder than they actually were. 

“We don't know why this happened, but our brain takes in all these different sensory inputs and then interprets how hard we feel like we are working. Perhaps adding cognitive stimulation during activity is just another input that shifts perception of effort,” says Aslan. 

At the same time, not all participants reported a higher RPE during the exercise-cognitive session. The day before the exercise trials, the participants completed a suite of cognitive exams that assessed their memory, visuospatial skills, and problem-solving. These specific cognitive abilities are vital for activities like hunting and gathering—and endurance sports or long, physically demanding jobs. The research team noticed that those who performed well on the initial exam did not report an increased RPE. These participants did not perceive the exercise-cognitive session to be any more tiring than the exercise-only session. 

This finding suggests that at some point in our evolutionary history, our bodies developed strategies to mitigate perceived exhaustion when modern humans started hunting over further distances. How our bodies manage this is unknown, but this new discovery inspires researchers to design interventions for anyone to optimize their endurance by leveraging mental as well as physical workouts. 

Daniel Lieberman, a paleoanthropologist at Harvard University who did not contribute to the study, says “We tend to think that physical activities are distinct and separate from cognitive activities such as thinking. But they are not. And experiments such as this that look at how exercise and cognition interact are both fascinating and important for mind-body connections.”

Prior research has shown how physical activity can improve brain function, but little is known about the inverse: how cognitive abilities can improve endurance. It may be just as important for an athlete's stamina to strengthen mental resilience as it is to improve cardiovascular fitness. 

So, the next time you go on a run or walk, whether that be on a treadmill or on a hiking trail, consider doing a Sudoku or Wordle or finding your way without your phone. As Aslan emphasizes, “Instead of training endurance and learning separately, these results are a first step in trying to motivate people to stay cognitively engaged during physical activity, which may have important health benefits for your brain and body.” After all, as Daniel Lieberman concludes, “we evolved to think and move at the same time."

You can read the original study here:

D.H. Aslan, L. Fenton, S.D. Han, M.H.C. Lai, D.M. Luong, T. Markarian, A. Seshadri, G.E. Alexander, & D.A. Raichlen, Cognitive correlates of human endurance, Proc. Natl. Acad. Sci. U.S.A. 122 (47) e2512055122, https://doi.org/10.1073/pnas.2512055122 (2025).