Mental Fatigue Can Impair Physical Performance

Mental fatigue impacts many things in your day-to-day life, so it isn't a surprise that it could also be holding you back in training.

By Elizabeth Millard |

  • A new study suggests that high levels of mental fatigue can impair your cycling performance.
  • Experts suggest easy ways to avoid this detrimental effect to your rides, particularly when it comes to your screen time.

If a mentally exhausting day makes you feel less inclined to exercise—or you feel like you’re not performing your best when you do—it’s not your imagination. A new study in the International Journal of Sports Physiology and Performance suggests that too many mentally demanding tasks can have a significant effect on how well you exercise.

Researchers looked at the effects of mental fatigue in 16 men and women by asking them to complete complicated cognitive tasks before weight-training exercises, and then again before doing a 20-minute cycling time trial. They also assessed performance in these activities without mentally challenging tasks done beforehand.

After measuring variables like mood, distance cycled, power output, heart rate, and blood lactate, researchers found that even when their performance results were consistent, participants had an increased rate of perceived exertion when mental fatigue was a factor. That means despite performing well physically, they may cut a workout short because it feels harder than usual, according to lead author Christopher Ring, Ph.D., researcher at the School of Sport, Exercise, and Rehabilitation Sciences at the University of Birmingham in the U.K.

“We’ve known for a long time that the brain, and especially perception, play a part in sports performance, but this highlights how mental fatigue can cause a significant change,” he told Bicycling. “Interestingly, we didn’t see physiological changes that would impair performance, it was only mental fatigue that reduced endurance for tasks like resistance training and cycling.”

Also notable is that previous studies have shown brief bursts of activity, like sprinting or jumping, is usually unaffected by mental fatigue, and so is strength training under three minutes, Ring said. It’s when an activity requires endurance that the amount of cognitive weariness kicks in and potentially impairs performance.

What is mental fatigue?

In terms of what constitutes mental fatigue generally, he said the standard definition is a psychobiological state caused by demanding cognitive tasks, leading to lack of energy or impaired cognitive function. Within that framework, Ring said this type of fatigue can be subjective, depending on what each individual considers mentally tiring.

“For example, athletes might be browsing on smartphones before training or during breaks,” he added. In itself, that might not lead to mental fatigue, but if the content they’re consuming requires a high degree of mental effort, it could be a stealthy drain on their overall brain power—and, subsequently, on their endurance, Ring said. That’s why the researchers recommended that athletes and coaches develop greater awareness of the role that mental fatigue might be playing in performance.

Mental fatigue may have a greater ripple effect as well, according to previous research. For instance, a study in BMC Neuroscience noted that the condition can lead to daytime drowsiness, difficulty concentrating, decreased alertness, disordered thinking, slow reaction times, reduced work efficiency, and more errors on work tasks.

How can you address mental fatigue?

Another study, in Frontiers in Psychology, suggests that the effects of mental fatigue can persist for at least 20 minutes—in that research, reaction time was slowed due to the condition, but gradually improved with time.

That research helps explain a good strategy for those looking to support their performance even after mentally demanding tasks, according to Paul Nestadt, M.D., assistant professor in the department of psychiatry and behavioral sciences at Johns Hopkins School of Medicine.

“Sometimes, simply waiting for a short time, like half an hour, between mentally demanding tasks and a workout might be beneficial,” he told Bicycling. “Building in a kind of ‘mental rest period’ before switching tasks may have a greater effect than you think.”

If you still believe performance is being sabotaged by mental fatigue, he suggested developing habits that can decrease your fatigue levels overall. For example, take more work breaks throughout the day—even if it’s just a few minutes at a time—and get more movement, more often, which tends to be stimulating for the brain.

Larger, long-term strategies include addressing sources of stress, improving sleep behavior, and considering a switch to a brain-healthy eating plan. For example, the MIND diet was developed as a way to bolster function for the brain during aging.

Most of all, just be aware of signs that you’re overloading your mental capacity on a regular basis. This can include symptoms like anxiety, difficulty sleeping, trouble focusing, rampant distraction, and a lowered sense of resilience in general. Nestadt said paying attention to shifts in mood—getting irritated more easily is a red flag, he added—as well as motivation for any tasks, not just exercise, can indicate that you need to build more mental breaks into the day.

If you want to level up, Ring suggested that brain endurance training could be advantageous. This is a type of neurological training that’s more focused than just taking breaks—it helps focus the brain on controlling impulses, reducing distractions, and improving reaction time.

A randomized controlled trial published in the Journal of Science and Medicine in Sport, which also involved Ring, found that this type of training—which they also defined as engaging in cognitive tasks during exercise—improved endurance performance more than physical training alone.

Ring said that until brain endurance training is more accessible and easier to implement on your own, a good first step might be to put the smartphone down for at least 30 minutes before your next ride.

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