Over recent decades, leading theories of human behavior have been applied across various physical activity (PA) settings, yielding mixed results. While they have provided some valuable insights, they have largely failed to achieve one central aim - to help foster sustained, population-wide increases in PA (Albarracín et al., 2024; Ekkekakis & Zenko, 2016; Pratt et al., 2020; Rhodes et al., 2019). This gap has prompted concern, as these theories, despite some support for their assumptions, have not translated into meaningful and lasting behavior change. Some have criticized them for their overarching dependency on the decisional balance one may perform given the right set of conditions (e.g., supportive social environments; benefits vs. barriers dyad; self-efficacy appraisal) (Conn et al., 2011; Ekkekakis, 2017; Rhodes et al., 2019); others have pointed to an astonishing lack of experimental efforts testing the expression of those theoretical assumptions (Ekkekakis et al., 2019; Manninen et al., 2022; Ntoumanis & Moller, 2025), leaving researchers, policymakers and stakeholders (and the theories) hostage to cross-sectional and longitudinal evidence. Either way, new approaches and experimental efforts to address the challenge of supporting PA practices are warranted and urgent.

Three of the most studied motivational theories in PA contexts over the last decades are the Theory of Planned Behavior (Ajzen, 1991), Self-Determination Theory (Deci & Ryan, 1985), and the Transtheoretical Model (Prochaska & DiClemente, 1984) (Ntoumanis et al., 2018; Simpson et al., 2025). Without minimizing their usefulness and robust body of evidence, they fall into the category of theories that have struggled, to date, to demonstrate moderate or large effects in programs aiming to improve exercise-related behavior based on their assumptions. Naturally, the complexity of each theory or model brings several challenges that undermine the extent to which we can confidently attribute any limited effect observed in an experimental study solely to the theory's inability to express its assumptions. As such, despite decades of research grounded in several (conceptually) well-established behavioral theories, there remains a need to test their assumptions through experimental approaches and, complementarily - or if necessary, alternatively - to explore new avenues for inquiry and theoretical development (Simpson et al., 2025).

To this end, the present study will address this issue experimentally using two theoretical approaches. The first approach is grounded in a well-established theory of human motivation, Self-Determination Theory (SDT), which offers numerous recommendations for its potential application, particularly in promoting positive impacts on exercise adherence. The second approach is structured in alignment with the general principles of hedonic theory, a recently revitalized approach to the understanding of Human behavior, focusing on the promotion of pleasurable responses during exercise.

Inclusion Criteria:

Professionals

- All exercise professionals in the three clubs

Exercisers

• > 18 years old
• All exercisers enrolled in the three clubs
• A subsample of the first 174 voluntaries participating in the study and enrolled in the three clubs after September 1st

Exclusion Criteria:

• Expulsion of the clubs due to internal rules violation or other decision independent of this study