Mental fatigue lies at the core of motivating yourself to hit the gym and to give the extra push in your athletic performance. In Workout Motivation: The Science of the Brain's Role in Exercise we broadly introduced the importance of our mind for exercise performance. The interconnectedness between the brain and body means many markers of physical performance are modulated by our mind.
Sports performance metrics, such as power, muscular endurance, reaction time, and processing speed are all influenced by the brain. Even the motivation to workout in the first place is governed by our mental energy.
The goal of this article, Stay Motivated to Workout, is to focus on mental fatigue, introduce you to some of the fatigue models (how scientists believe the brain is operating), explain willpower and self-control and how they interact with workout motivation, and provide actionable tools to help you follow through on a workout program.
Motivation Tip: Understand the Cause of Mental Fatigue
It makes sense that mental fatigue would influence metrics like reaction time, processing speed, or focus. It is more surprising that mental fatigue can decrease endurance and strength performance, but that is what Dr. Ranjana Mehta found.1
According to the research, when participants were given mentally fatiguing questions while in the process of working out, mental fatigue decreased strength performance by 10 - 66% and endurance performance by 25%.
A 2017 review of 11 studies analyzing mental fatigue and physical performance confirmed these results.2 The authors identified “...higher than normal perceived exertion.” as the culprit hurting endurance performance.
There are two potential explanations for why this happens. One of them is that the more mentally tired you are, the higher the signaling rate (how much the brain talks to the muscles in order for them to perform). This makes us feel like we have to work harder physically.3
The other hypothesis is that the brain processes effort differently when your brain is suffering from mental fatigue, which makes the workout seem more difficult than it actually is.
For example, the sensation of fatigue—burning legs, wheezing lungs—is amplified, the brain decides “this is enough” and exhaustion sets in.4 We may be physiologically fine (our body is capable of doing much more), but we are mentally unable to go further.
The main thing to remember is that mental fatigue makes workouts feel more difficult, so we do less and perform worse. The flip side you can utilize these tools to motivate yourself to workout and give an extra push in your workout program by minimizing mental fatigue before and during exercise.
Two Models of Mental Fatigue
There are two main models of mental fatigue that explain some of the research discussed above.
Central Governor Model
One theory suggests the brain regulates physical exertion controlling our output so we cannot threaten our safe homeostasis (central governor model). This is a top-down theory whereby the brain is keeping us safe from harm, but doing so subconsciously. A researcher named Tim Noakes proposed this theory. Listen to his podcast with Ben Greenfield to learn more.
In the psychobiological model, theorists observe that people exercise until high levels of perception of effort, disengaging from exercise without physiological failure or disengage because they believe the task to be physically impossible.5 This is done at a conscious level (related to our perception). This may be a feature (or explanation) of how the central governor model works.
Both are important (though theoretical) models of mental fatigue that provide some understanding of the inner workings of your mind. While the models disagree on some aspects of the “how” and “why,” they agree on the big picture: increased mental fatigue results in decreased athletic performance.
Science of Willpower for Workout Motivation
No discussion of workout motivation would be complete without tackling willpower and self-control. Our ability to maintain self-control to actually workout, to finish the workout as planned, and workout with the intensity that brings us to physical exhaustion is a huge determining factor in our success. It may also be a finite resource.
According to researcher Roy Baumeister, willpower and self-control is limited. In 1998 he published his findings and coined the term “ego depletion,” which suggested that self-control waned over time.6
This gave rise to the idea that willpower might be like a reservoir. Each act of self-control—whether it’s trying to do one thing or to not do something else—taps into this reservoir. This leaves less self-control available for other things that require willpower.
People have a hard time maintaining self-control over long stretches of time. As I mentioned in The Science Behind Workout Motivation, many people join a gym or start an exercise program in January and find themselves skipping workouts by February. But depleting willpower doesn’t just occur over weeks or months. It can play out over the course of a day.
For example, I don’t frequently eat calorically dense foods (i.e., “junk” food), but when I do, it is in the evenings and night. My self-control, which has been exerted all day, starts to fail in the evening and the plantain chips or chocolate bar suddenly seem conscionable. In a sense, I drained my self-control reservoir by using it for things during the day and don’t have enough to counter these tempting foods at night.
This concept of “ego depletion” is also the source of the phrase “willpower is a muscle.” The thought is that our willpower or self-control is a trainable skill that can be “strengthened” over time (and like other muscles can become fatigued if we use it too much).
Another model of motivation called Self-Determination Theory (SDT) builds on the idea of willpower being a finite resource.
In 2007, researchers Richard Ryan and Edward Deci published a paper in the journal of Social and Personality Psychology Compass explaining that “ego-depletion” is more nuanced than Baumeister suggests.7 Their research focuses on “vitality” (a term they use for physical and mental energy). They propose that the degree of depletion of vitality and energy is determined by the source of motivation for the behavior.
The key is, the “why” behind what we are doing matters. According to Ryan and Deci intrinsic motivation (being the best version of myself, self-respect) doesn’t deplete our willpower nearly as much as extrinsic motivation (how I look, what someone said about my body). We can reward ourselves with deeper willpower reservoirs by focusing on intrinsic motivation.
In other words, if we perform a fatiguing task due to a deeply held interest or value, then willpower will not be depleted (and in some cases can even be enhanced).
During extended water fasts, I experience this. As the fast becomes more physiologically challenging, my levels of confidence and pride go up (because fasting is a deeply held value). My behavior becomes more robust over time despite having less physical and mental energy. I will not discount physiological changes (metabolism of fatty acids etc) that influence my mental state, but there is a definite psychological boost that I experience.
Willpower Tips: Gain Workout Motivation
In part 3 and 4 of this series, we will focus on nootropics and ergogenics (supplements that improve physical performance), but there are strategies we can use to get that extra push without supplements that may support our levels of mental fatigue and willpower.
For one thing, shorter, more high intensity workouts don’t require as much mental energy as longer workouts. According to Dr. Jeroen Van Cutsem, “...the shorter and more maximal the task, the lower the impact of mental fatigue.”8
This means we can minimize the role mental fatigue plays on exercise performance by the type of exercise we perform. One way we can access more sustainable gym motivation is by doing high interval intensity training (HIIT), which is high intensity, low duration activity.
When I have waited too long to workout or I feel short on time, I will often do sprints for four minutes. The routine is 8 sprints, all out for 20 seconds and then 10 seconds rest in between. It can be incredibly challenging for less than a 5 minute workout.
We can do things during the workday to make sure we keep mental fatigue in check. This is especially important when you plan to exercise after work. Having more mental energy available at the end of the day can improve your workout: it might also make the difference in whether you do it.
According to Dr. Angie Fifer, it’s possible to combat mental fatigue throughout the day by taking short breaks. She suggests “...focus intensely for 20 minutes with a five-minute break.”9 According to a 2011 study in Cognition, brief mental breaks do slow mental fatigue.10
During a short break it’s better to do something that is different than work (as opposed to similar to it). This means that if work entails sitting at a desk using a computer, a break where you are sitting looking at a smartphone might not counter mental fatigue as much as going for a short walk outside.
Finally, consider your motivations for working out. Is it because there is something you desire for yourself or is it for others? We don’t necessarily need a gym buddy or personal trainer to give us workout motivation, and sometimes all we require to be successful in our workout plans and weight loss goals is a little empathy for our future self. Consider the future you and how they might like to feel and perform. You may look back and thank yourself.
1 Page 32 of 38. https://uwaterloo.ca/centre-of-research-expertise-for-the-prevention-of-musculoskeletal-disorders/sites/ca.centre-of-research-expertise-for-the-prevention-of-musculoskeletal-disorders/files/uploads/files/fatigue_ranjana_mehta.pdf