The Next Chapter Was Waiting at the Gym
In a fascinating experiment involving 226 participants, researchers explored how access to an enticing audiobook could serve as an incentive to increase gym attendance. The study, conducted by Katherine Milkman, Julia Minson, and Kevin Volpp, was published in 2013 and later appeared in Management Science in 2014 under the title “Holding the Hunger Games Hostage at the Gym.”
Participants were divided into three groups: one group could only access audiobook-loaded iPods at the gym, a second group received audiobook access with encouragement to restrict listening to workouts, and a third group acted as a control with no audiobook incentives. The gym-only group initially increased their gym visits by 51% compared to the control group, a notable early boost in attendance. However, this advantage diminished over time, especially following Thanksgiving, indicating that the effect was an initial attendance spike rather than sustained behavioral change or improved fitness outcomes.
A Reward Available During the Task
This study is a prime example of “temptation bundling,” a behavioral strategy that pairs an immediately gratifying activity with one whose benefits feel more remote. By combining the enjoyment of an engaging audiobook with the act of exercising, the pleasure becomes part of the workout itself, rather than a reward dispensed only after completing it.
The timing of the reward is crucial. A prize promised after a month of exercising requires patience, whereas an absorbing story playing during the workout makes the session more appealing in the moment. For temptation bundling to succeed, two factors are essential: the reward must be genuinely desirable to the participant, and the activity must allow for its enjoyment.
As highlighted in Wharton’s detailed account of this research, Milkman emphasized the difficulty in sustaining the initial benefits and re-engaging participants after breaks. Importantly, the study’s university participants had already expressed a desire to exercise more, which is a key context when considering the results.
In essence, the story provided a compelling reason to return to the gym.
The Break Reveals Why Follow-Up Matters
Behavioral interventions often succeed in improving initial decisions but fail to establish lasting routines. Interruptions—such as holidays—disrupt established patterns and access to supportive elements like the audiobook incentive. Observing how effects change following such breaks provides valuable insight into the durability of behavior changes.
It’s important to note the experiment did not isolate the impact of holidays from the passage of time, so the decline cannot be attributed solely to the interruption. Still, the timing of the effect’s reduction after Thanksgiving is a meaningful indicator that breaks challenge sustained engagement.
For those developing behavior-change programs or products, this underscores the necessity of measuring beyond launch periods. Tracking performance during the initial week, over the subsequent month, and after interruptions can uncover distinct obstacles. Both initial appeal and the ability to successfully restart after a lapse require dedicated attention, even within a single intervention.
A Larger Trial Tested a Lighter Version
Building on the original concept, a 2020 field experiment involving 6,792 participants extended the idea across a four-week exercise program. Participants were assigned to one of three conditions: an audiobook with explicit encouragement to listen while exercising, an audiobook alone, or no audiobook at all. The results revealed that the audiobook-plus-encouragement group increased their likelihood of working out weekly by approximately 10% to 14%, and their average weekly workouts rose by 10% to 12% during the program and a follow-up period extending to seventeen weeks.
The benefit of explicitly explaining temptation bundling was modest compared to simply providing the audiobook. Researchers suggested that receiving an audiobook as part of an exercise program might implicitly encourage combining the two activities, reducing the added impact of the formal encouragement.
This intervention differed fundamentally from the university study’s approach of restricting audiobook access to the gym. The less restrictive model is easier to scale, allowing participants freedom to listen elsewhere, but this also changes the nature of the behavioral nudge. The later study’s results reflect this lighter, more flexible approach rather than replicating the original arrangement.
Returning After a Missed Visit Is Another Target
Further expanding on gym attendance behavior, a 2021 Nature megastudy examined 54 four-week digital programs among 61,293 members of a U.S. fitness chain. Nearly half of the interventions significantly increased weekly gym visits, with gains ranging from 9% to 27%.
The most effective intervention offered small rewards specifically for returning after a missed workout, highlighting the importance of targeting recovery from lapses alongside initial motivation. While this study’s findings cannot be directly compared to the audiobook trial due to differing participants and programs, collectively these insights stress that starting, continuing, and restarting behaviors represent distinct challenges that should be addressed individually.
Measure the Behavior the Product Actually Changes
Using gym entry as a measurable, concrete outcome allows researchers to track observable behavior. However, it does not capture workout intensity, duration, or direct health improvements. Clear and transparent reporting that separates the measured action from hoped-for outcomes is essential for accurate interpretation.
This principle applies broadly beyond exercise: for example, app opens, lesson completions, and skill retention are related but different metrics. A product might influence initial engagement without guaranteeing long-term mastery or health benefits. When testing pleasant pairings like temptation bundling, it is critical to define upfront which behavior matters and to verify whether effects persist over time.
The audiobook experiment demonstrates a compelling possibility: that an activity people already intend to do can become more attractive when paired with something enjoyable. Its diminishing effect over time also highlights a practical question for implementation: how to encourage participants to return after interruptions disrupt the routine.
