In an until-recently classified report funded by the UK’s Ministry of Defence, researchers revealed something remarkable: you can reap enormous performance gains by altering your perception of effort—and anyone can do it.

Historically, scientists and athletes have thought of the stress that leads to fitness gains as being physical—training longer, running faster, or jumping higher. In recent years, researchers have begun to explore the mental component of training—how visualization can improve performance. But until now, few researchers have examined how mental stress can lead to training adaptations similar to physical stress.

In the MOD study, thirty-five soldiers trained three times a week on stationary bikes for the experiment, riding each time for the same duration and intensity relative to their own baseline fitness. In addition to the physical effort, half of the soldiers were also asked to engage in a mentally demanding task—watching combinations of letters appear on a computer screen and clicking only when certain combinations appear—while they pedaled.

At the end of the 12-week study, both groups showed comparable increases in V02 max, a common indicator of physical fitness. This makes sense since the training regimens were physiologically identical. However, when the soldiers completed a “time to exhaustion test” in which they rode at a constant effort—80 percent of their respective VO2 maxes—for as long as possible, things changed.

The group that had trained without the mentally demanding task improved their time to exhaustion, on average, by an impressive 42 percent. Soldiers who clicked letter combinations on the computer during their workouts, however, improved by a whopping 126 percent—three times as much as the control group.

That’s because the soldiers doing the mentally challenging activity—the "Brain Endurance Training" group—were actually “training themselves to tolerate a harder perceived effort, so when the cognitive task was removed, the effort felt easier,” says Dr. Samuele Marcora, an expert on fatigue who oversaw the study. “Something unique was happening inside the heads of the BET group.”

If you stress your brain at the same time as your body, when you get rid of the mental stress, the physical training seems easier.

That something, he believes, is the strengthening of the Anterior Cingulate Cortex (ACC), a part of the brain associated with perception of effort. “You strengthen that part of your brain and increase your tolerance for effort,” Marcora says, “so that when the cognitively straining task is eliminated, you are able to endure a much greater physical load.” In other words, if you stress your brain at the same time as your body, when you get rid of the mental stress, the physical training seems easier.

Rodent studies back up Marcora’s belief in the effort perception role of the ACC; mice with damaged ACCs become so lazy that they stop attempting to overcome obstacles in the way of food.

The good news is that you don’t have to read Latin or follow streaming letters on a computer screen while training in order to see a performance enhancing effect. Simply compelling yourself to pay attention to a meaty article like this one or a highbrow audio book while training—when you’d rather be zoning out—likely provides benefits. This is especially great news for busy athletes with day jobs; reading your morning briefing or reviewing a PowerPoint during your training session may actually improve your physical performance later on.

This does not mean that all workouts should be paired with a mentally-demanding task. “The best athletes know how to look inward, read their bodies, and really focus,” says Dr. Michael Joyner, an expert on physiology and human performance at the Mayo Clinic. “While learning to maintain physical effort in spite of cognitive strain can certainly be beneficial, there is also something to say for really focusing on what you are doing— what is happening inside your body—when you are training hard and wanting to get the most out of your physical self.”

Marcora agrees, suggesting there are “certain situations where brain training in combination with physical training makes sense and certain situations where it does not.” More specifically, if you are going to do all-out intervals, it is probably best to focus solely on the intervals, perhaps with some music blasting in the background. But, if you are doing an easier or more moderate workout—anything up to 80 to 85 percent of maximum effort—that’s prime time to work your brain. “Applying a cognitive strain can produce an enhanced training effect without adding any additional physiological stress,” Marcora says.

The most exciting aspect of this research is that it opens up a new frontier for athletes. “When it comes to performance improvement and the traditional physiological model, there is hardly anything left to be gained,” says Marcora. “Innovation will come from a different approach.”