Overweight and obesity are today considered among the most important health risks facing humanity with more than one in two adults overweight or obese in western countries. In addition, Type 2 diabetes mellitus (T2DM) is a common comorbidity associated with overweight and obesity and counts for 5% of the French population under 65 years of age and 15% in people over 65 years old. Despite the accumulation of scientific evidence supporting the benefits of physical activity, obese and diabetic people remain insufficiently active and current programs struggle to engage and sustain physical activity of patients over long periods of time. It is therefore urgent to develop interventions that can effectively change individuals' behavior. In this context, "e-health" interventions and gamification appear to be a particularly promising avenue to improve physical activity and reduce attrition rates of current programs.

This clinical trial aim to test the effectiveness of a digital intervention based on gamification and teamwork in comparison to a supervised physical activity program. The investigators hypothesized that the intervention will be efficient by the development of a self-determined motivation through the process of gamification on the one hand. On the other hand, through the in-group collaboration with other people who share the same stigmatized criteria that will help participants to overcome weight stigmas, acting generally as physical activity barriers.

This trial is a randomized, two-arm intervention design that will examine the efficacy of a digital group-based intervention based on gamification and teamwork among obese and T2DM patients. The experimental arm will be compared to an active control group representing the traditional care program (supervised physical activity).

The digital intervention is composed of four components within a smartphone application: a) a gamification of PA, b) a remote adapted physical activity program with telecoaching sessions, c) an interface for exchange and conversation and, d) an activity monitoring tool. Accelerometer data, self-reported PA, body composition, and physical capacities will be assessed before, at the end of the intervention and then at the issue of a 6-month follow up. To advance our understanding of complex interventions like gamified and group-based ones, this study will explore several psychological mediators relative to motivation, enjoyment, in-group identification, or perceived weight stigma. Finally, to assess a potential superior efficiency compared to the current treatment (face-to-face supervised PA), this study will include a cost-utility analysis between the two conditions.

Inclusion Criteria:

• Subject affected for obesity (BMI ≥30 kg/m² and <45 kg/m²) and/or T2DM.
• Subject treated at the University Hospital of Clermont-Ferrand.
• The participants must have an iOS (at least iOS8 version) or Android (at least version 5) smartphone.
• Subjects must also be able to provide informed consent to participate in the research and be covered by health social security.
• Subjects must be native to any physical activity intervention.
• Sufficient proficiency of French will be required to ensure the understanding of the questionnaires.

Exclusion Criteria:

• Medical or surgical history judged by the investigator to be incompatible with the study.
• Subject with an unstable psychiatric condition.
• Pregnant or breastfeeding women.
• Heavy alcohol consumption (> 2 to 3 drinks per day depending on gender) or drug addiction.
• Disability or contraindication to PA.
• Subject with cardiorespiratory and/or osteoarticular disorders that limit their ability to perform physical tests or moderate PA for 30 minutes.
• Subject with progressive cardiovascular or neoplastic disease.
• Subject who has presented a major infection in the 3 months prior to inclusion.
• Subject with a known neuro-muscular pathology (i.e., myopathy, myasthenia, rhabdomyolysis, paraplegia, hemiplegia).
• Subject with chronic or acute inflammatory pathology within 3 months prior to inclusion.
• Subject diagnosed and/or treated for schizophrenia, bipolar disorder, major depression.
• Subject deprived of their liberty by judicial or administrative decision.
• Subject refusing to sign the written consent to participate.
• Subject participating in another study.

We will share de-identified data associated with the collected samples by depositing these data at the Open Science Framework (OSF) repository. The storage will be in Germany (Frankfurt). Data will include demographic, anthropometric, and physical measurements along with data from questionnaires and intervention adherence. We agree that we will identify where the data will be available and how to access the data in any publications and presentations that we author about these data.

Data will be available via a public OSF project that will be accessible by everyone. We agree to deposit outcome data into the OSF repository as soon as possible but no later than within two years after the completion of the trial or upon acceptance of the data for publication, or public disclosure of a submitted patent application, whichever is earlier.

Research assistants collecting data will be blinded to the treatment allocation. Double blinding is nevertheless not possible in such interventions because allocation concealment is impossible for participants.