Believing Willpower Is Limited Makes Clients Choose Easier Workouts

If you coach people for a living, you've heard the line a hundred times: "I don't have the willpower today." It sounds like a statement of fact, like saying you're out of petrol. But a study published this month suggests that sentence isn't describing a fuel gauge at all. It's describing a belief, and that belief is doing more work than most of us realised: it's steering which workouts, sets and challenges a person is even willing to attempt in the first place.

The study

Researchers at the University of Vienna (Christopher Mlynski, Georgia Clay, Julia Jankowski and Veronika Job) set out to test something that hadn't been directly studied before. There's a well-established line of research on "lay theories of willpower": some people implicitly believe self-control is a limited resource that gets used up (the "ego depletion" model), while others believe effort and self-control are energizing, the more you draw on them, the more capable you become. Prior work had shown these beliefs affect how well people perform on a second demanding task after a first one. What nobody had tested was whether the belief affects whether someone chooses to take on a hard task at all.

The team ran four studies, published in the Journal of Experimental Psychology: General (Vol. 155, Issue 4). Three were correlational, pooling 1,461 participants who completed a questionnaire measuring their willpower beliefs and then worked through a mental arithmetic task where they could pick their own difficulty level across multiple rounds. The fourth was a preregistered experiment with 442 participants, meaning the researchers locked in their hypotheses and analysis plan before collecting data, a safeguard against quietly reshaping the story after seeing the results. In that study, participants were randomly assigned to read materials framing willpower as either a limited resource or a nonlimited, energizing one, before doing the same task-selection exercise.

What they actually found

The pattern held across all four studies. People who endorsed a nonlimited-resource view of willpower consistently chose harder arithmetic problems than people who saw willpower as something that depletes, and this held even after the researchers statistically controlled for how good participants actually were at math (their "math self-concept"). In other words, this wasn't just confident people picking hard problems and less-confident people picking easy ones. It was specifically about their theory of effort itself.

Even more telling: when the researchers tracked choices across the task, people with nonlimited beliefs kept escalating the difficulty they chose as rounds went on, while people with limited-resource beliefs plateaued at easier levels and stayed there. And in the fourth study, where willpower beliefs were experimentally induced rather than just measured, the causal arrow held up: people nudged into the "energizing" framing chose tougher problems afterward than those nudged into the "depleting" framing.

The authors frame this as evidence that lay beliefs about willpower have large-scale implications for goal setting and effort-based decision-making, not just for how well you perform under strain, but for whether you sign up for the strain in the first place.

The caveats worth sitting with

This is a well-designed study: four studies, a large combined sample, and a preregistered experimental arm that gives real causal weight to the correlational findings. But it's worth being honest about what it doesn't show. The task was mental arithmetic in a lab or online setting, not a barbell, a long run, or a diet plan sustained over months. Translating "chose a harder math problem in a 20-minute session" to "showed up for leg day in week nine of a cut" is a reasonable inference, not a proven one. The belief-induction in Study 4 was also a single, brief manipulation; the researchers didn't test whether a nudge like that produces a belief change that lasts weeks or months, which is the timescale that actually matters in coaching.

It's also worth remembering this sits inside a broader, genuinely contested debate. The original "ego depletion" idea, that willpower is literally like a muscle that fatigues with use, took a serious hit from a large multi-lab replication effort last decade that found the classic depletion effect was much smaller and less reliable than first believed. This new study doesn't resolve that debate; it sidesteps it cleverly by showing that regardless of whether willpower "really" depletes, believing it depletes changes behavior on its own. That's arguably the more useful finding for a coach anyway: you can't directly edit someone's neurochemistry, but you can influence what they believe about their own capacity.

Why this matters in a gym or an app

Think about how often a client's self-talk sounds exactly like the "limited resource" framing in this study: "I used up my discipline hitting my step count today, so I'm skipping the gym." "I can't add another hard set, I'm cooked." "I only have so much motivation in me this week." If this research is right, that isn't just a description of how they feel: it's actively shrinking the difficulty of what they're willing to attempt next, set after set, week after week, the same way the low-belief participants quietly plateaued on easier arithmetic instead of pushing further.

The flip side is the opportunity. Coaches are, functionally, in the belief-shaping business as much as the programming business. The language you use around effort, like "that set's going to fire you up for the rest of the session" versus "just get through it, you're almost out of gas," isn't just motivational fluff. Per this study's logic, it's shaping the actual mental model your client uses to decide how hard a thing to choose next.

What to actually do with this, starting this week

Listen for depletion language in check-ins and coaching conversations, phrases like "I'm out of willpower," "I don't have it in me today," or "I used up my discipline already," and treat it as a flag, not just a complaint. It's a live data point about which theory of effort that client is currently operating from.

When you're introducing a harder set, a heavier week, or an optional finisher, frame it in energizing terms rather than depleting ones. Small wording shifts, like "this is going to build your capacity for what's coming" instead of "just push through, you're nearly done," mirror exactly the kind of reframing the researchers used to shift behavior in Study 4.

Give clients real choice over difficulty where you can, the way the study's task did: a genuine "pick your challenge" moment on an AMRAP, a rep range, or an optional extra round. Then watch the trend over weeks: are they steadily reaching for more, or plateauing at the same comfortable level? That trajectory is diagnostic. A client who keeps choosing the same easy option consistently across sessions is a much better use of a mindset conversation than a client whose numbers are just quietly climbing.

Be careful with your own coaching clichés. Phrases built around scarcity, like "save your energy," "don't burn out too early," or "you've only got so much in the tank," are well-intentioned, but this research suggests they may be reinforcing exactly the belief structure that makes people choose less, not more.

None of this replaces good programming. But it's a reminder that two clients with identical fitness levels can end up choosing very different training lives based on a belief neither of them has ever said out loud.

Sources and references

• Mlynski, C., Clay, G., Jankowski, J., & Job, V. (2026). Lay beliefs of willpower shape individuals' propensity to approach or avoid effortful tasks. Journal of Experimental Psychology: General, 155(4), 939-950. PMID: 41538141. DOI: 10.1037/xge0001885
• Markman, A. (2026, September 10). Beliefs About Willpower Affect Whether You Try Hard Tasks. Psychology Today. Read the summary
• For background on the contested "ego depletion" (limited-resource) model this study sits alongside: Hagger, M. S., et al. (2016). A Multilab Preregistered Replication of the Ego-Depletion Effect. Perspectives on Psychological Science, 11(4), 546-573. Summarized in Scientific American: Observing Others' Self-Control Can Sap Your Own

This article summarizes peer-reviewed research for general educational purposes. It is not a substitute for individualized coaching, medical, or mental health advice. If you or a client is experiencing significant burnout, exhaustion, or mental health symptoms, please consult a qualified professional.