It’s endurance training day, and you and your Spartan buddies have come (mentally exhausted) straight from your desk job for the day’s real work: a two-hour run punctuated every 15 minutes by sets of 20 burpees. With human nature being what it is, chances are that one — or, more likely, all of you — will try to lower expectations for your coming performance by cataloging how much toil you’ve already endured at your day job.

“You guys won’t believe how much cargo I loaded today,” boasts the baggage handler.

“Bags are nothing,” retorts the piano mover. “Try heaving baby grands all day.”

Meanwhile, you — a veteran desk jockey — have spent the last 10 hours sitting in an ergonomic office chair, staring at spreadsheets and financial models. The only thing you’ve lifted is your right hand, and only to smack yourself on the forehead in frustration. You're mentally exhausted and your gumption is faltering. How can you possibly compete in the lowered-expectations game? You can — and win easily, in fact.

Related: How to Unleash Your Inner Spartan If You Work at a Desk All Day

British researchers recently discovered that your route to being mentally exhausted may have taken as big a toll (if not bigger) than your buddies’ physical labor. In research published in The Journal of Applied Physiology, investigators equipped 16 highly-fit volunteers with monitoring apparatus to assess everything from respiratory and heart rates to lactate levels and cardiac output. Half the subjects were then randomly assigned to watch a 90-minute documentary and the other half to take a 90-minute computer test. Immediately afterward, both groups were asked to ride to exhaustion on a stationary bike. Two days later, all the volunteers came back to the lab and switched roles.

Being Mentally Exhausted Degrades Physical Performance

None of the volunteers knew at the time what the point of this study was. Researchers, for their part, have understood for decades that an exhausted brain becomes increasingly inept in executing numerous cognitive tasks. But this was the first study to examine whether induced cranial brownout might also degrade physical performance.

Related: Why You Feel Tired in the Afternoon — and How to Prevent It

To accentuate the difference in pre-exercise mental work, the British investigators purposely selected a documentary designed to soothe rather than challenge the brains of the viewers — not so for the computer test. That was designed to guarantee mental exhaustion.

The results proved eye-opening in two ways. First, mental fatigue took a huge toll on physical performance, with post-test volunteers reaching physical exhaustion 15 percent sooner on average than they had after watching the documentary. Second, the reasons for this were completely unexpected.

Related: 6 Ways to Energize Yourself in 60 Seconds

“Prolonged mental exertion did not cause any changes in their cardiovascular, respiratory, or metabolic responses,” lead author, Samuele Marcora, Ph.D., of the University of Kent’s Endurance Research Group, said. “In this study, the only factor that could explain their premature exhaustion was a higher perception of effort experienced by the mentally-fatigued subjects.”

The technical term for this is RPE, or rating of perceived exertion. There’s a strong “mind over matter” components to peak exercise performance, and an exhausted “mind” just can’t overcome “matter” as well as a fresh one can. Your brain-draining day at the office, in other words, won’t tax your physical capacity the same way piano lifting does. But it does make exercise feel an awful lot harder.

So what can you do about being mentally exhausted? Here are some tips from Marcora and his colleagues on how to avoid mental fatigue and build mental strength:

1. Go Hard, Not Long

On days when your brain is fried, focus on strength training or high-intensity intervals versus long-and-steady training.

“One of our studies on neuromuscular function found that mental exhaustion’s negative impact seems limited to endurance exercise,” Marcora said. “It doesn’t appear to hurt short, maximal efforts such as sprints and jumps.”

Related: Functional Interval Training: The HIIT Circuit for Core Stability

2. Exercise Before Thinking

If you work a cognitively-demanding job, consider working out before you go to the office. Morning people often report that exercise before work can prove mentally-strengthening and refreshing, even making them more productive. If, however, you have no choice but to exercise after work, cut yourself some slack. It’s completely normal to have less stamina at such times, Marcora said.

3. Beware of Inhibition

Some mental challenges are more taxing than others. One in particular, “response inhibition” or suppressing actions, can take an outsized toll. In another study on endurance capacity, volunteers took either an easy computer test (all they had to do was push a button when the right answer flashed on screen) or a hard test (which included trick answers that required the test-takers to suppress the urge to push the button inappropriately). The volunteers who did the easy test averaged 80 seconds faster on a 5K run that followed.

Related: Spartan Running Training Plan | Day 27: PR Your 5K

“Athletes should avoid tasks involving response inhibition before competition,” Marcora said.

One way to do that is to avoid interactions where you might be forced to hold back or suppress a response.

4. Taper Your Brain

Workouts are one thing — major competitions are another. Most athletes practice some form of physical taper in the weeks leading up to important events, reducing the volume of exercise and giving their bodies a chance to rebuild. Given the connections between mental fatigue and reduced endurance, you might want to give your brain a chance to rest up a little too, Marcora said, in order to build up your mental strength.

Not only will your muscles perform better, but your brain may perceive that it takes less effort to do so.

Related: Resting Your Mind the Spartan Way

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