Have you ever participated in (or at least WATCHED others participate in) an obstacle race?

Some big ones that come to mind are the Tough Mudder, the Spartan Race, and the aptly named Rugged Maniac, just to name a few.

If you are just observing, it can be really entertaining. When competitors get fatigued, they start making a LOT of mistakes, both mentally and physically. They slip, stumble, wobble, bumble, flounder and topple—all in the name of entertainment.

Of course, if you happen to be one of the competitors, it may not be all that funny if you are serious about winning. STILL … it can definitely make for a great highlight reel later on when you are able to finally laugh about it.

There are probably dozens of life lessons that can be learned from these challenges, but one that sticks with me the most is the impact of muscle fatigue and how eerily similar that is to the way our inner world works as well.

In his fascinating book WILLPOWER: Rediscovering the Greatest Human Strength, Dr. Roy Baumeister shares lessons on how to focus our strength and redirect our lives.

In what became one of the most cited papers in social science literature, Dr. Baumesiter discovered that willpower actually has a physical basis and operates a lot like a muscle: it can be strengthened with practice … and it can be fatigued by overuse.

It doesn’t take much of an imagination to see the potential applications of such a theory.

One example mentioned in the book is that psychologist Don Baucom observed that marriages seem to have the most trouble when stress at work is at its worst. His conclusion is that people were using up all their willpower on the job. They gave at the office—and their home suffered the consequences.

What exactly IS willpower, though? What parts of the brain are used? Which neural circuits? What are the physical changes?

At the risk of oversimplifying, one specific portion of the brain called the Anterior Cingulate Cortex (or ACC) seems to be the primary conflict monitoring and error-detection system of the brain. What Dr. Baumeister discovered is that through exertion of willpower, we have what he called EGO Depletion: a clearly diminished capacity to regulate our Thoughts, Feelings, and Actions. In other words, in this depleted state, there is an actual slowdown in the ACC (that self-control mechanism). It’s pretty easy to identify, because there is a noticeable change in the overall intensity of your feelings. For example, if you find yourself especially bothered by frustrating events, or saddened by unpleasant thoughts, or even happier than normal about some good news—then maybe, says Dr. B, it’s because your brain’s circuits aren’t controlling emotional responses as well as normal.

Another key finding is that STRESS actually depletes willpower. He says that there’s a common misperception that stress causes you to become grumpy, irritable, and prone to anger or despair. But what stress REALLY does, he says, is deplete willpower, which diminishes your ability to control the inner world that creates those emotional responses. Not only that, but once your willpower is diminished, your cravings start to feel stronger than ever. In other words, you are more easily tempted. It’s a double whammy!!

So, after studying thousands of people, the conclusions were simple:

Willpower is finite and is depleted with use.

You use the same stock of willpower “energy” for many things, but in FOUR broad categories:

1. We need willpower to control our THOUGHTS
2. We need willpower to control our EMOTIONAL reactions
3. We need willpower to control our IMPULSES (this is what we stereotypically think of when we think about willpower: resisting temptations) AND
4. We need willpower to control our PERFORMANCE (this is basically task perseverance with just the right combination of speed and accuracy)

So, what happens when we experience this “ego depletion”? Do we just get a pass for poor performance?

Well, I think we probably need to be a little more gracious towards one another even on our best days. But that isn’t really the point. The point is that willpower is a natural, God-given way to keep us from slipping, stumbling, and wobbling; bumbling, floundering and toppling.

Where Does Willpower Come From?

At one stage in my life, my family and I lived in the Orlando area for almost 10 years. Honestly, it was a blast. I love warm weather and sunshine, so that made it pretty easy to begin with. And despite the crowds and the traffic and the endless sea of tourists, Orlando can be a really fun place to live. We had season passes to Universal and Islands of Adventure a couple of years. We had season passes to Seaworld a few years. And we got connected to Disney’s “extras” casting list and so we were able to visit those parks once a twice a year for free (in exchange, of course, for being extras on whatever it was Disney happened to be filming).

But it didn’t take living in Orlando very long for me to learn something about myself: After about 4 hours in a theme park, I was DONE. D-O-N-E, done. Hot, tired, sticky, hungry, and overwhelmed by the crowds, all I wanted was to go back home, which annoyed my poor wife and children to no end.

Then one day we had a “deluxe” Disney experience thanks to some VERY generous friends. We took a leisurely pace, ate three insanely delicious gourmet meals at Disney’s best dining experiences, had snacks and drinks all day long … the works.

After 12 hours in the park, I STILL felt like the day had just begun. I was energized!

So, that experience taught me that eating good would make the difference in my endurance … but I never really understood why until I read the research by Dr. Baumeister that I mentioned earlier.

According to Dr, Baumeister, in their early eagerness to chart the brain as the human equivalent of computers chips and circuits, most psychologists had neglected one mundane but essential part of the machine: the power cord. In a computer, chips and circuit boards are useless without a source of energy. And so is the brain. That energy source is glucose.

For example, a healthy immune system uses small amount of glucose energy to function. But when you’re sick, your body uses gobs of energy. That’s why sick people sleep so much and why their brains are in a fog; their body uses all the energy—derived from glucose—to fight the sickness.

For the brain to even function correctly, all that thinking requires glucose in the bloodstream. That is, in turn, converted into neurotransmitters.

In both children and adults, research has shown that that low self-control is associated with a big drop in the brains fuel of glucose.

No glucose, no willpower. Let me say that again: No glucose, no willpower.

It’s a pattern that has showed up time and again as researchers have tested more people in more situations.

Researcher Heather Thames even figured out that ego depletion (which I also talked about earlier) actually shifts activity from one part of the brain to another. In other words, your brain does not stop working when glucose is low. Think of it like an episode of Star Trek or some other sci-fi show: in low power situations, the person in charge calls for “all available power to be diverted from [blah-blah-blah]” and into some other more critical area for the scene (life support, thrusters, weapons … whatever). The brain works the same way in low power situations: it simply stops doing some things and starts doing others instead.

So, in the book, WILLPOWER, Dr Baumeister suggests 5 strategies for putting glucose to work for you.

1. Feed the Beast. Eat good, particularly on days when you’re physically or mentally stressed. Do not take on that challenge without glucose. You really aren’t yourself when you’re hangry. Don’t skimp on calories when you’re trying to deal with serious challenges.
2. Skip the Sugar. Sugar may seem like the fast approach to more glucose, but a sugar spike is promptly followed by a crash. Then you are worse off than when you started.
3. When you eat, go for the slow burn. The body converts just about all sorts of food into glucose, but at different rates. Foods that are converted quickly have a high glycemic index, producing boom and bust cycles, leaving you short on glucose and self-control. For steady self-control you’re better off eating foods with a low glycemic index: vegetables, raw fruits like apples, blueberries, and pears, cheese, fish, meat, olive oil, etc
4. When you’re sick, save your glucose for your immune system. Don’t trust the glucose-deprived brain to handle anything important.
5. When you’re tired, sleep. Adults routinely shortchange themselves on sleep, and the result is less self-control. Research has shown over and over that sleep deprivation impairs your ability to effectively process glucose.

The next time you find yourself feeling like the old version of me in a hot Florida theme park—D-O-N-E, done; hot, tired, sticky, hungry, and overwhelmed, don’t risk a crash and burn situation where you might say and do things you will later regret. Instead, maybe you should consider how full you “self-control” tank is—or isn’t—at the moment, and provide your brain with the energy it needs to continue to function at high levels. If you do this, you’ll be much more likely to face that challenge head on and still come out on top.