Exercise and Willpower: Why the Motivation Problem Runs Backwards

A 2025 study found that four weeks of high-intensity interval training improved self-control and reduced ego depletion in college students. If the finding holds, the “I don’t have the willpower to exercise” complaint may describe a problem that exercise itself would solve. Interestingly, exercise and willpower are more closely linked than most people assume.

Ting Fan and Geng Li put 104 college students through twelve sessions of high-intensity interval training over four weeks at Hunan Normal University. Eighteen minutes per session, three times a week, average peak heart rate of 162 beats per minute. Nobody dropped out. Before the programme, Fan and Li measured each student’s self-control and ego depletion levels, then measured again after the final session. Both had shifted, and not by a small margin: self-control was up and ego depletion was down, each at p < .001. Therefore, the results support the relationship between exercise and willpower. They show how both can improve together.

Every gym owner knows the speech. Someone signs up in January, shows up for three weeks, then cancels their next session. If you ask them why, the answer lands on willpower. They have run out of it, work has been relentless, and they will come back once things settle. The industry has a playbook for this, which usually involves finding a reason, setting a goal, and launching some kind of six-week transformation challenge. All of it assumes the same thing. Willpower is fuel and you need a full tank before you can train.

Fan and Li’s study, published in Acta Psychologica in 2025, belongs to a long and unresolved argument about willpower. Roy Baumeister proposed the ego depletion model. In this model, self-control works like a muscle, fatigues with overuse, and can be rebuilt through training. Oaten and Cheng tested this with exercise back in 2006 and found something that went further than fitness gains. Students on structured exercise programmes became better at self-regulation in areas that had nothing to do with the gym. It was as though the underlying capacity had grown.

Ego depletion: The theory that self-control draws from a limited mental resource that becomes temporarily exhausted through use. First proposed by Roy Baumeister. Contested by multiple failed replication attempts, most notably a 2016 multi-lab study led by Hagger et al.

Their broader survey covered 1,032 students across four Chinese universities. Negative life events predicted higher ego depletion and lower self-control, which was expected. What separated the students was exercise. Those who trained regularly held up better under stress than those who did not. Furthermore, physical exercise moderated the entire relationship between stressful events and ego depletion, as if it were taking some of the load before the stress reached their self-control. This demonstrates that exercise and willpower interact in complex ways, benefiting students’ resilience.

None of this is clean. Ego depletion as a concept has been in trouble since 2016, when a multi-lab replication led by Hagger found no detectable effect. The resource model that Baumeister built has been losing ground steadily. Fan and Li’s own intervention had no control group, so the gains might be regression to the mean, expectation effects, or just the passage of four weeks. Their measures were self-report scales, not behavioural tasks. Every participant came from the same Chinese university. Against all of that, a separate 2025 study in Frontiers in Public Health ran a different HIIT protocol over eight weeks with 58 participants at a different university and landed on the same result for self-control. Two independent groups designed different studies and got the same direction. That does not prove the case. However, it is harder to write off as coincidence. After all, the ongoing research into exercise and willpower shows the scientific community is still exploring this connection.

Think about the member who cancels their 6pm session because they feel hollowed out after work. By their own accounting they are being sensible, conserving a supply of willpower they believe is already spent. Every gym ad, every motivational poster, every “find your why” campaign confirms the framing: you need willpower to get through the door.

Fan and Li’s data says the door is where you get it back. Therefore, the member waiting to feel ready enough to train is waiting for the thing that training provides.

“I’ll start Monday” is the most common sentence in the fitness industry every January, and it describes a loop: members wait for willpower to accumulate before they act, and the waiting is precisely what stops it from accumulating. If this research holds, the willpower they think they need to spend on training is willpower that training would produce.

The members waiting for motivation before they book a session might be waiting for something that only the session can give them.

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References

Fan, T., & Li, G. (2025). The effect and mechanism of physical exercise on ego depletion in college students. Acta Psychologica, 260, 105652. https://doi.org/10.1016/j.actpsy.2025.105652

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If you’re wondering what’s happening in your members’ heads before they cancel, the Cognitive Bias Library is a good place to start. In summary, understanding exercise and willpower can shed light on members’ motivations and behaviours.