The Science of Willpower

Research supports the notion that willpower works like a muscle—so how do you train it?

What do the following acts have in common?

  • choosing the healthy items at the breakfast buffet and ignoring the pastries and fried food
  • smiling and saying, “Let’s see if I can help you with that,” when an angry client blows a minor issue into a major complaint
  • sticking to a budget, even after your initial enthusiasm for improving your finances has waned, and the sale at your favorite store is beckoning
  • staying on the treadmill for the time goal you set, even though each minute is a little harder than the last

Each of these acts requires willpower—the ability to ignore temporary pleasure or discomfort to pursue a longer-term goal. It’s easy to agree that these challenges require inner strength, but where does that strength come from? And why is willpower such a fickle friend, supporting us on some occasions and abandoning us on others?

Fifteen years ago, Roy F. Baumeister, PhD, now a researcher at Florida State University, set out to answer these questions. He pitted several possible models of willpower against each other, and when the dust of his early studies settled, the results supported a surprising model. According to Baumeister, willpower is not a personality trait, a skill or a virtue. Instead, it operates like a muscle. And as such, it can be strengthened—but also easily exhausted (Baumeister 2003).

This “strength” model of willpower has important implications for fitness and wellness professionals who seek to inspire and support healthy behavior in others. By understanding how willpower can be strengthened, you can find new strategies for helping clients meet their goals. And by understanding why willpower is necessarily limited, you can identify ways of supporting behavior change without exhausting willpower.

A strength model of willpower proposes four important ideas:

  1. Willpower is a mind-body response, not merely a mindset.
  2. Using willpower depletes resources in the body.
  3. Willpower is limited.
  4. Willpower is trainable.

Let’s consider each of these ideas; the evidence that supports them; and how they can be applied to health behaviors.

Willpower Is in the Mind and Body

Mind-body responses are coordinated physiological changes that allow you to adapt to some challenge. The best-known mind-body response is the fight-or-flight response to stress or danger—heart racing, blood pressure soaring, muscles tightening and senses heightened (Sapolsky 2004). The relaxation response, in contrast, allows the body to respond to its internal needs of digestion, growth and restoration (Benson 1975).

Suzanne Segerstrom, PhD, a psychologist at the University of Kentucky, was one of the first researchers to study the biological basis of willpower. Segerstrom’s research has begun to identify changes in the autonomic, cardiovascular, neuroendocrine and immune systems during acts of willpower. Segerstrom says it’s possible that these changes are part of a coordinated whole-body response that helps us adapt to challenges requiring self-control. She calls it a “pause and plan” response. This mind-body response would allow us to temporarily freeze our impulses and focus on our long-term goals.

What’s going on in the body that helps us slow down and proceed with intention, not instinct? One important process is heart rate variability (HRV), or the beat-to-beat fluctuations in heart rate. In one study, Segerstrom required participants to flex their willpower by eating carrots and resisting cookies (Segerstrom & Solberg Nes 2007). Successful participants showed a temporary increase in HRV as they were exerting their willpower, followed by a drop afterward. What’s more, participants who had higher HRV when they joined the study showed greater willpower.

Why would higher HRV assist self-control? Changes in HRV are determined by the autonomic nervous system’s balance of sympathetic activation (responsible for the fight-or-flight response) and parasympathetic activation (responsible for the relaxation response). High HRV reflects a healthy, flexible activation of both systems (Appelhans & Luecken 2006). Maintaining high HRV in the face of a self-control challenge might represent a kind of inner strength and stress resilience—the ability to focus attention (as in the fight-or-flight response) but also to stay calm (as in the relaxation response). The result: acting in line with our highest goals, and not with our immediate appetites.

Willpower Depletes Resources in the Body

The mind-body response of exerting willpower literally fatigues us (Tice et al. 2007). It depletes physical power, as shown in one study that looked at the effects of mental self-control on physical stamina (Bray et al. 2008). In this study, trying to control one’s thoughts decreased muscular endurance, as measured by performance and EMG activity. The researchers who conducted this study called the effect “central fatigue.”

Our minds and bodies draw from the same source of strength. But what is this source? Matthew Gailliot, PhD, a researcher at the Univer­sity of Amsterdam, argues that the fuel of willpower is glucose. In a way, this should be no surprise, since glucose is the primary fuel of the body. It’s the same fuel that skeletal muscles use to exert their strength, and the same fuel that the brain uses to perform its many tasks. What is surprising is the fact that willpower uses a lot of it, even when the body is at rest. According to Gailliot, willpower is a particularly expensive mental act, engaging many areas of the brain and requiring high levels of fuel (Gailliot et al. 2007).

Gailliot and his colleagues have demonstrated that simple acts of self-control both require and lower blood glucose levels. In one recent set of studies (Gailliot et al. 2007), participants were required to control their thoughts, emotions or behavior. Immediately following each act of self-control, participants’ blood glucose levels dropped. Levels did not drop dur­-ing similar tasks in which participants were not exerting self-control. Participants were then asked to repeat the acts of self-control. Those whose blood glucose levels had dropped the most from the first task performed the worst on the second attempt. Participants given a sugary drink between tasks (replenishing their blood glucose levels) were better able to exert their willpower in the second attempt.

This study certainly pushes the boundaries of how we think about willpower. Not many of us would like to believe that our virtue is dependent on the last time we snacked. However, the implications are important: our ability to flex our willpower depends on the availability of blood glucose. When blood glucose levels are low (for example, from skipping breakfast), or when the body has impaired use of glucose (as in diabetes or the increasingly common metabolic syndrome), willpower is impaired. Numerous studies confirm that low blood glucose levels and poor glucose use are associated with worse self-control of attention, emotions and behavior (Gailliot et al. 2007).

Does this mean we should be giving ourselves sugar every time we want to exert some self-control? Clearly, that would be a short-sighted strategy. In their report of this research, Gailliot and his colleagues recommend a more reasonable strategy: choose foods that keep blood glucose levels relatively stable, and don’t skip meals.

The Limits of Willpower

The studies described above point to a troubling idea: willpower is inherently limited. No matter how physically fit we are, exerting ourselves inevitably leads to exhaustion. The same is true of inner strength: self-control depletes willpower in much the same way that exercise temporarily depletes physical power.

This observation comes from numerous studies over the last decade that test the limits of people’s self-control (for a research review, see Baumeister 2003). In these experiments, people who exerted their willpower on one occasion struggled to do so a second time. Studies have found this effect with all sorts of self-control tasks, including turning down tempting foods, suppressing emotions and persevering at challenging problems. The conclusion: the willpower “muscle” gets fatigued.

Taking the strength model literally, fitness pros might be curious: Do we have separate willpower “muscles” for different types of self-control? Does it take a different kind of strength to resist gossiping than it does to get up early to exercise? Or do all acts of self-control draw on the same source of strength?

According to willpower researcher Suzanne Segerstrom, PhD, “Willpower is general. People may differ in how tempting they find chocolate cake or slouching, but you don’t have separate will ‘powers’ for refusing chocolate cake and for sitting up straight.” Research backs this up—the same studies that show how willpower is limited also show it doesn’t matter whether you control your temper or your craving for a cigarette—exerting willpower in one area limits your ability to do so in all others.

Because willpower is limited, each act of self-control is a win-lose effort, helping in the immediate situation but making us more likely to lose control later. Refraining from gossiping at work makes it more difficult to hit the gym after work. Resisting the impulse to splurge at your favorite store makes it more difficult to turn down dessert.

This means that it’s important to set priorities and to give ourselves a break on the things that aren’t at the top of the list. Fitness and health coach Chris Freytag, a member of the American Council on Exercise board of directors, says this strategy is especially important in the United States, where we receive the message that it’s possible to have it all and do it all. According to Freytag, this message gets in the way of real change. “It’s the whole American attitude of all or nothing. We have no middle ground. If you change everything, it’s really hard to comply—it’s too much stress in your life. You can only control so many things.” Freytag counsels people to aim for progress, not perfection.

Willpower is also affected by whatever is going on in our lives. Coping with any kind of stress depletes willpower (Gailliot et al. 2007). For example, Kathleen Vohs, PhD, formerly a researcher at the University of British Columbia and now assistant professor of marketing at the University of Minnesota, has shown that having to control our image can deplete willpower (Vohs, Baumeister & Ciarocco 2005). Managing our self-presentation in professional or social settings—especially when repressing our natural personality—takes a toll on our ability to meet other goals.

Social stress takes a particularly large toll on willpower. One set of studies has shown that people who are lonely or socially rejected have worse control over their thoughts, emotions and health-enhancing behaviors (Baumeister et al. 2005). For example, socially rejected participants were less likely to resist the temptation of freshly baked cookies, and they quit a challenging task sooner than participants who were not rejected. Research also shows that feeling stigmatized depletes willpower for both mental and physical acts of self-control (Inzlicht, McKay & Aronson 2006).

Why might loneliness or feeling stigmatized—whether because of race, gender or weight—keep us from our goals? Brain-imaging studies show that social rejection impairs areas of the brain that are important for focusing attention and pursuing goals, leading to worse self-control (Campbell et al. 2006). Other researchers have argued that social rejection takes away the will to exert willpower, draining motivation as much as strength (Baumeister et al. 2005).

Aimee Kimball, PhD, director of mental training at the University of Pittsburgh Medical Center’s (UPMC) Center for Sports Medicine, says this research confirms what she has observed when motivating sedentary adults to become active through UPMC’s START program. “Social support is really important for developing willpower,” says Kimball. She encourages people to share their goals and celebrate their successes with friends, co-workers or family. She also counsels clients to simplify other things in their life. “I ask them to write a list of things that stress them out, and make a plan for the things they can control. If there’s something on the list they can’t control, I ask them to cross it off so they don’t waste energy on it.”

Restoring Willpower

Is there anything we can do to restore willpower once we’ve exhausted our strength? One strategy seems obvious: get adequate physical rest. And, in fact, research suggests that sleep does restore depleted willpower (Baumeister 2003). This is particularly important to keep in mind when asking clients to make a challenging behavior change. Trying to do so without enough sleep is like trying to drive a car without gasoline.

Michael Krugman, founder and director of the Sounder Sleep System, agrees that addressing insomnia and insufficient sleep is a crucial component of any health program. “When we’re sleep deprived, our resolve weakens and we seek the path of least resistance. We spontaneously revert to unhealthy habits that can be performed automatically, with less mental and physical effort.” A good example of this is diet: people who sleep only 4 hours a night are less likely to choose foods based on health, weight or ethical concerns (Wells & Cruess 2006). If you need the strength to take the more difficult path, you need proper rest.

Research also shows that a small boost in mood restores willpower depleted by a recent act of self-control (Tice et al. 2007). For example, in one study, participants’ willpower was depleted by the experimental equivalent of dieting: they were left alone in a room with radishes, cookies and chocolate, and were encouraged to help themselves—but only to the radishes! Participants were then asked to perform a challenging mental task. Participants who watched a short comedy video between the two tests of willpower persevered longer in the challenging task.

In another study by the same researchers, participants who received a gift from the experimenters (a small bag of candy tied up in a ribbon) had better willpower for consuming a “health” drink that tasted like vinegar. Why did a spoonful of sugar make the medicine go down? The researchers argued that the happy surprise re-energized depleted stores of willpower (Tice et al. 2007). It’s a well-known strategy to reward ourselves after we’ve followed through with a new healthy behavior. But it might be an even better idea to reward ourselves first, and use the mood boost to follow through.

These strategies—get enough sleep, laugh, focus on the positive, and treat yourself—may not be new, but even the best advice needs to be packaged in an appealing way. Thinking of these strategies as little “booster shots” of willpower can motivate your clients to follow them more consistently and can give people a sense of greater control over their willpower reserves.

Increasing Willpower

If willpower is like a muscle, then it should be trainable through “exercise.” According to the physiology of fitness, temporarily exhausting a muscle should lead to increased muscle size or improved ability to use fuel. Is the same true for willpower?

Researchers have put this to the test with willpower training regimes (Baumeister et al. 2006). These interventions take a simple approach: ask people to control one thing that they aren’t used to controlling, and to do it every day. Like physical exercise, this act of self-control can be uncomfortable at first, but over time it is no longer a struggle. The willpower muscle has learned a new skill, and with practice, the act of self-control is less likely to deplete willpower.

If all acts of willpower reflect a single strength, then training any individual act of self-control should strengthen all acts of self-control. Indeed, this is what research shows. Committing to small, consistent acts of willpower in any domain—from improving our posture to watching our finances—can increase overall willpower (Muraven et al. 1999; Oaten & Cheng 2007).

For example, Megan Oaten, PhD, and Ken Cheng, PhD, researchers at Macquarie University in Sydney, Australia, investigated the benefits of an 8-week willpower training program that required participants to create and meet artificial deadlines (Oaten & Cheng 2006a). Participants not only improved at time management; they also ate a healthier diet, increased their physical activity levels and reduced tobacco, alcohol and caffeine use. Importantly, these health behaviors were not addressed in the intervention. The primary training effect appears to have been improved willpower endurance. Researchers Oaten and Cheng argue that the training made participants less susceptible to willpower depletion and therefore better able to take care of themselves.

We’ve been talking about “exercising” willpower, meaning exerting it in any way. But what about actual physical exercise? Although it’s sometimes hard for fitness professionals to imagine, the great majority of people find exercising unpleasant and difficult. So showing up for a workout—and sticking with it even when tired or bored—requires willpower. And according to the strength model of willpower, exercise should also temporarily exhaust willpower reserves. Over the long-term, however, it should lead to increased strength or endurance of the willpower “muscle.”

This prediction is supported by recent studies examining the effects of physical exercise on willpower. In a study by Oaten and Cheng (2006b), participants were given free gym membership and personalized training programs. After 2 months, participants who kept up with the exercise program also reported improvements in a wide variety of behaviors requiring willpower, from eating a healthier diet to controlling their temper to reducing substance use and impulsive spending.

But what if you like to exercise? Will working out still improve your willpower? Consider this: regular physical exercise can increase heart rate variability (Buch, Coote & Townend 2002) and improve blood glucose control (Snowling & Hopkins 2006). The form of the exercise doesn’t seem to matter, as long as it’s consistent. Recent studies suggest that mind-body exercise, such as yoga, is also effective (Khattab et al. 2007, Shapiro et al. 2007).

Willpower researcher Matthew Gailliot, PhD, agrees that physical exercise could improve willpower by enhancing HRV and blood glucose control. However, no research has directly tested this possibility. Researcher Suzanne Segerstrom, PhD, advises, “Until we understand more about it, exercise might be the best bet for improving willpower, because it covers both bases.” Add that to your list of reasons everyone should be physically active!

Conserving and Bypassing Willpower

If willpower is inherently limited, it makes sense to conserve it. But it doesn’t make sense to simply give in to temptation right and left. How can you make healthy choices without depleting willpower?

Margaret Moore, founder and chief executive officer of Wellcoaches® Corporation, teaches her clients to plan in advance as a strategy for conserving willpower. “You don’t want to be standing in front of the fridge saying you don’t have a clue what to eat. The weakest moment of self-control is when you’re hungry and tired. Too much choice tends to overwhelm us. If you have to make a lot of choices, you’ll deplete your self-control.” This advice is backed up by recent studies showing that any type of decision making—even choosing among brands of candy or shampoo—can deplete willpower (Vohs et al. 2008).

Moore recommends organizing your life so you don’t have to think about what you’re going to eat or whether you’re going to exercise. Make healthy choices in advance, and in moments of greatest strength. This is a strategy you can share with clients. For example, plan your dinner before you come home hungry and exhausted from work. Set up a weekly date to meet a friend at the gym, and don’t consult your temptation to stay home. Commit and just show up—no choice and no willpower needed.

Another strategy is figuring out how you will deal with obstacles. One study found that people who wrote in a journal about how they would handle barriers to exercise were more likely to stick with an exercise program (Sniehotta et al. 2005). A second study found that this approach helped people succeed at a challenging self-control task after a previous task had depleted their willpower (Webb & Sheeran 2003).

Sports mental health trainer Aimee Kimball, PhD, says this is an important aspect of preparing people to start and stick with an exercise program. “I ask them to identify obstacles to their goals, so they can make a plan.” Kimball also asks clients to visualize themselves following through with their plans, so that success seems not only possible but inevitable.

This is a process you can apply to any self-control challenge. Deciding what you will do when tempted sets up a kind of reflex response. You don’t have to think about what you will do—you just use the challenge as a cue to implement your planned strategy. For example, you might decide in advance that every time you are tempted to eat before bed, you will take a hot bath instead. And then when you get the craving, it’s a signal to take a bath, not hit the fridge.

Finally, it may be possible to face a challenge by completely bypassing the willpower system and drawing on a different source of strength: motivation. The best way to do this is to focus on the positive reward of a behavior rather than the sacrifice or effort. Health coach Margaret Moore takes a big-picture approach to positive motivation: “I ask clients to ask themselves, ‘Who do I want to be? Who is my best self when it comes to health and well-being?’ People need to have some self-image in mind. I also ask them to figure out ‘Why do I care? What’s the higher purpose? What will being healthy give me that my life will not be great without?’ That’s the heartfelt piece that people don’t typically connect to. If people don’t get moved emotionally, if they don’t know what they want, then they’re not going to succeed.”

Limits and Possibilities

The idea that willpower is inherently limited is a tough idea for many people to accept. We’d rather believe that our own inner strength is limitless and that if we just try hard enough, we can kick any bad habit, stick to any diet and follow any fitness program, while simultaneously winning friends and influencing people. It’s also tempting to look at those who don’t succeed at a goal and judge them as being unwilling or weak. But if everything from stress to blood sugar levels can get in the way of willpower, it’s no wonder we aren’t all self-control superheroes.

This shouldn’t be taken as bad news, and it doesn’t mean we’re all doomed to self-control failure. A strength model of willpower gives you and your clients a realistic and creative way to plan for success. Among the top lessons of the research are the following:

  • Willpower is limited, so it’s important to set reasonable goals and priorities. Conserve your willpower for what really matters.
  • Forgive temporary setbacks. A single mistake doesn’t mean you are weak. It may just mean you’ve already succeeded to the limits of your current ability, and now you deserve a rest or reward to restore your strength.
  • Recognize that willpower is not “all in the mind,” and supply your mind-body with the fuel it needs to face life’s challenges. This fuel includes rest, a healthy diet and a steady supply of positive experiences.
  • Understand how the demands of your job, family and other relationships may interfere with your (and your clients’) ability to stick with a health or fitness program. Look for ways to reduce stress in all areas of your life to support any major life change.
  • Conserve or bypass willpower by focusing on other strengths: planning, commitment and positive motivation.

SIDEBAR: Why Diets Fail

Think of the typical diet: you’re required to repeatedly avoid foods you love and show incredible self-restraint around other people who aren’t dieting. Who has the strength to exert unrelenting willpower, especially when life presents so many other challenges that require self-control? Research shows that chronic dieters are especially susceptible to overeating when faced with an abundance of tempting food, specifically because they view eating as a constant act of self-control (Vohs & Heatherton 2000).

Traci Mann, PhD, associate professor at the University of Minnesota who studies dieting and other forms of self-control, says, “The majority of people will not be able to succeed at a severely restrictive diet because it is simply too hard. It’s just unsustainable.” Mann recommends that people make smaller but meaningful changes in their diets, such as cutting out just one type of unhealthy food or reducing calorie intake by only 200 calories a day. “These types of changes are not as painful and don’t require as much self-control, so people may be able to sustain them longer.”

Giving yourself breaks from willpower—for example, taking 1 day off a week to indulge in your favorite foods—might also replenish your resources to resist temptation. Health and fitness coach Chris Freytag, author of Prevention’s Shortcuts to Big Weight Loss (Rodale 2007), says, “You have to give yourself a little satisfaction every now and then. If you deprive yourself all the time, something’s going to give. You have to pick your battles.”

Kelly McGonigal, PhD, teaches psychology, yoga and group fitness at Stanford University. Contact her at kmcg@stanford.edu or www.openmindbody.com.

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Kelly McGonigal, PhD

IDEA Author/Presenter
June 2008

© 2008 by IDEA Health & Fitness Inc. All rights reserved. Reproduction without permission is strictly prohibited.

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