The goal of this clinical trial is to learn if an exercise program before bariatric surgery works to treat obesity, could improve physical condition and weight loss before bariatric surgery and induce a lifestyle behavior change. The main questions it aims to answer are:

• Does a supervised exercise program lead to improved physical condition prior to bariatric surgery?
• Does a supervised exercise program prior to bariatric surgery lead to reduced surgery related complications?
• Does a supervised exercise program prior to bariatric surgery lead to maintained lifestyle changes after surgery?

Participants will:

• Receive either no training program or physical exercise training program twice a week, supervised by a physical therapist, for a duration of 8 weeks.
• Have their fitness measured at the start and at the end of the 8 weeks, measured with a six minute walking test.
• Fill in a survey on their perceived quality of life and exercise habits at the start of the trial, and at 1 year after surgery.

Inclusion Criteria:

• Adult patients (≥18 years)
• Body-Mass-Index (BMI) 40 kg/m2 or higher, or 35 kg/m2 or higher with the presence of at least one comorbidity (type 2 diabetes, high blood pressure, heart and/or vascular diseases, obstructive sleep apnea (OSA), dyslipidemia, or arthritis).
• Primary bariatric patients; without previous bariatric surgery. For inclusion the investigators will follow the National Guidelines on metabolic surgery.

Exclusion Criteria:

Patients with:

• mobility problems (patients who are not able to exercise)
• cognitive disabilities
• illiteracy (patients who are not able to read and understand the language of the country where the study will be performed)