Mental Fatigue Can Easily Sabotage Your Endurance

Samantha Lefave


Logging kays after a hard day’s work may feel like a stress-reliever – but it could be sabotaging your run. |

Think about the last time you went for a run. What were you doing before it? Maybe you were waking up from a bad night’s sleep, or you’d just finished an intense project at work, or you’d spent the better part of an hour scrolling through Instagram. Though it may not feel immediately apparent, all of these things are mentally draining, and could be sending your brain’s fuel tank to ‘E’. Worse still, when you lace up for a few kays in this state of mind, research shows that your workout suffers.

A recent review of 11 studies published in the journal Sports Medicine found that when you’re mentally fatigued, your overall performance in endurance workouts and high-performance bouts – like a long run, or hill repeats – is negatively impacted.
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“We’re not able to continue to focus through the exercise session, because we’re tired from focusing so intensely prior to the workout,” says Angie Fifer, PhD, certified mental performance consultant with the Association for Applied Sport Psychology.

In one of the studies reviewed, researchers asked athletes to complete two workouts: in the first, subjects watched a 90-minute documentary that didn’t cause mental strain, and then cycled at high intensity to exhaustion. In the second, subjects worked on a computer task that required intense concentration for 90 minutes, then performed the same high-intensity cycling until exhausted.

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When the athletes’ performances were analysed, experts discovered that while physical measurements – such as heart rate, blood lactate, and oxygen consumption – weren’t affected by the mentally fatiguing task, psychological ones like perceived effort were. The latter workouts felt tougher, which resulted in athletes tiring more quickly, says study author Jeroen van Cutsem, PhD.

While he’s not able to say definitively what’s happening, Van Cutsem theorises that this increased perception of effort could occur because when you’re mentally tired, your brain has to boost how much it talks to your muscles in order to perform at the same level. That’s known as a higher signaling rate, and it makes it feel like you have to work harder physically. Another theory is that your brain processes effort differently when you’re mentally drained, which could also make the workout seem tougher.

It’s important to note, however, that mental fatigue isn’t the same thing as burnout – the latter is a chronic state of brain drain, one that’s triggered by things such as a consistently high workload, job insecurity, or little control of the daily things happening around you, says Van Cutsem.

Those things can all add up to emotional exhaustion and feelings of inadequacy, which can turn into long-term problems. Mental fatigue is acute, and happens when your brain is tired from prolonged periods – typically, 30 minutes to two hours – of demanding exertion.

“A tough day at work, having to work through a specific challenge or problem, or delivering a pitch or presentation can all cause mental fatigue,” says Fifer. “Basically, it’s anything that requires a significant amount of focus over an extended amount of time.”
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Before you worry about whether or not your brain is too tired for a workout (which, ironically, will only tire it out more), the upside is that not all workouts are impacted by mental fatigue. Van Cutsem says that the intensity is what matters. “It’s about endurance workouts versus all-out, maximum-effort ones,” he says. Short, all-out workouts (such as HIIT intervals) don’t require a lot of cognitive processing, so it doesn’t really matter how tired your brain is.

“The shorter and more maximal the task, the lower the impact of mental fatigue,” he says. It’s kind of like doing something before your brain even figures out what’s happening: busting out a 20-second high-intensity interval is mentally easier to push through than steeling your mind for a two-hour long run. So if your workout doesn’t require a ton of thought – it’s more about physically powering through – then that can be the better option on days you’re feeling mentally exhausted.

There are also ways to combat mental fatigue throughout your day, adds Fifer. Her biggest tip: structure your day with a break in between intense meetings or brainstorming sessions.

“While we think we can power through and get more done, it’s better for us mentally to manage stress and take short breaks,” she explains.

“The general rule of thumb is to focus intensely for 20 minutes with a five-minute break.”

And on days when you’re just not feeling like your head’s in the game, stick to your training schedule as intended and try to embrace the challenge by recognising the effort you put in to complete that run (even if it’s not your best). Van Cutsem says preliminary research shows that doing so might improve your resistance to mental exhaustion, resulting in greater mental toughness for important events – like race day.

Are You Mentally Fatigued?

Sadly, there’s no simple test that can definitely say your brain is too tired for a long workout, because, well, every brain is different. But Fifer says you should keep an eye out for a drop in motivation – especially if it doesn’t disappear once you start sweating.

“If you can’t get into a workout, that indicates that you may need to abort and try something different,” she explains. Listen to your perceived effort level that day, and be okay with mixing up your training schedule and speed if you need to.

Beat the Brain Drain

Here’s what the pros recommend.

Go in the morning.
After a good night’s sleep, an early run is one of the easiest ways to make sure you’re feeling mentally fresh, says Fifer.

Swish a sports drink.
A 2017 study found rinsing your mouth with a caffeine-containing drink before a workout resulted in higher resistance to mental fatigue.

Skip social media.

You don’t have to nix it altogether, but avoid scrolling right before you run, which can leave you irritated, suggests author Dr Amy Saltzman.

Centre yourself.
Instead of jumping straight from work to a run, use your commute to decompress and shift gears with mindful meditation, Saltzman suggests.

Or just breathe.
If your commute doubles as a workout, Fifer says taking deep breaths can recharge your mental batteries. Add them to your warm–up before running out the door.

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