Have you ever wondered why your workouts feel so much harder on certain days? Do you rack your brain trying to figure out why your performance suffered even though you’re fully fueled?
You may have noticed that the one common factor on your toughest training days is mental stress. In fact, research shows that mental fatigue has a markedly negative influence on athletic performance.
In a series of recent studies, both elite athletes and untrained individuals experience a significant drop in exercise performance after they’ve suffered mental stress. It’s not just one aspect of performance that is reduced either: Mental fatigue compromises most aspects of athleticism including time to exhaustion, power output, repeated sprint ability, sports-specific skills, and running speed.
In one recent trial published in the Journal of Applied Physiology, untrained men and women were asked to either watch an “emotionally neutral” documentary (this group served as the control trial) or perform a 90-minute cognitive test that is designed to induce mental fatigue and stress.
Then both groups did a time trial to exhaustion on a resisted stationary bike. Although the cognitive test didn’t produce any physical fatigue, the volunteers gave up on the cycling test 15 percent sooner when they were mentally fatigued compared to those that had simply watched the documentaries.
Surprisingly, the mentally fatigued group rated the exercise trial as significantly harder on a rating of perceived exertion (RPE) scale even though they quit cycling sooner than the control group. Additionally, the poorer exercise performance wasn’t mediated by physiological factors such as a higher heart rate or higher blood lactate. These physical responses remained largely unaffected, which means that the poorer performance and higher RPE wasn’t because the subjects were working harder.
Mental Fatigue Reduces Ability To Overcome Discomfort
Researchers theorize that mental fatigue reduces the subjects’ exercise tolerance, impairing their performance. There is a part of the brain called the anterior circular cortex (ACC) that regulates your “response inhibition.” This is your ability to overcome your instinct to pull away from discomfort.
Training, whether running a 400-meter sprint, lifting heavy loads for reps, or running a timed mile all require you to experience and overcome physical pain. The ability to push through physical discomfort is a mental skill, but it’s a finite resource. When you deplete it with a fatiguing mental work, whether with a cognitive computer test or writing a challenging work proposal, your athletic performance is going to suffer.
Perhaps the most important outcome from this study was that prior to the exercise trial, both groups scored the same in terms of motivation and they both chose the same level of resistance—mentally fatigued or not. This differs somewhat from how sleep deprivation affects motivation—training drive and self-selected difficulty is reduced when individuals are physically tired from lack of sleep.
The New Psychobiological Model of Fatigue
Researchers explain the results using a new psychobiological model of fatigue that views exercise limits as a balance between motivation and perceived effort: We stop not because our muscles are depleted of fuel or the weight is too heavy, but because the effort it would take to perform the task is greater than the rewards of continuing. A tired brain and tired muscles are equally capable of increasing your perceived effort and ultimately making you quit.
Intense cognitive work isn’t the only kind of work to compromise performance. Mental stress will do the trick as well. When volunteers were asked to hide their emotions while watching a disturbing video and then perform a time trial, they ran 3.3 percent slower and reported a higher sense of effort from the start. The need to suppress their natural emotional response left the subjects mentally fatigued and reduced their performance.
Even visualizing a tough workout in advance can leave your brain tired. We typically view mental imagery as performance enhancing, but this may only be true when we visualize effortless, powerful movements. Last year, when researchers had volunteers visualize a fatiguing workout and then perform an exhaustive endurance test, performance decreased by about 15 percent compared to a control trial.
What Can You Do About It?
Practically speaking, athletes should avoid mentally stressful activities prior to intense workouts or competition. Do everything you can to reduce difficult and mentally fatiguing experiences. If you are traveling for a competition, it may be worth it to plan all important factors in advance (where you’ll stay, eat, warm-up, train, etc.) and arrive as far in advance to avoid stressful decision-making tasks.
For the general population, it means that working out first thing in the morning might give you a better workout than after a long, demanding day at work. Or, if you prefer to work out at lunch or after work, it’s possible you could avoid the most mentally stressful tasks in the few hours pre-workout.
Scientists also believe its possible to train the brain to better withstand the effects of mental fatigue. A pilot study is currently testing the effect of having volunteers perform frequent computer-based cognitively demanding tests prior to an intense workout to see if they can enhance their ability to push through physical pain and boost performance.
The Three Best Supplements To Overcome Mental Fatigue
There are three supplements that can give you a lift to overcome mental fatigue.
Caffeine is the most studied and probably the most powerful. Similar to the effect it has on overcoming sleep deprivation, caffeine completely reverses the decline in physical performance caused by mental fatigue by blocking adenosine receptors in the brain that are linked to tiredness. Studies suggest that anywhere between 3 and 6 mg/kg will do the trick in habitual coffee drinkers and as little as 1 g/kg may be beneficial in people who don’t regularly consume caffeine.
Creatine is another powerful brain boosting nutrient that can help you overcome mental fatigue. Based on sleep deprivation studies, we know that mental fatigue leads to an immediate reduction in high-energy phosphates in that brain, leading to poor cognition and reduced central nervous system activity.
A single dose of 5 grams of creatine can replenish stores so that you can perform with normal precision, stamina, and power. Creatine has the added bonus of not raising cortisol or keeping you awake later as caffeine might due to its long half-life, making it ideal to use when you have to train in the evening after a long day at work.
Tyrosine is an amino acid may boost performance when mentally stressed. Tyrosine is a precursor to the catecholamine neurotransmitters that have an energizing effect on the brain and are quickly depleted during intense cognitive work or sleep deprivation.
In one study, researchers gave 150 mg/kg/bw of tyrosine to subjects in the military who were sleep deprived and had them perform a series of active performance tasks with a cognitive component. Tyrosine was able to offset declines in performance and vigilance that was not seen in a placebo group.