The primary objective of the study is to compare in a real-world setting the efficacy of traditional training (today's guideline, vigorously or moderate exercise) and amount of aerobic interval training (1-AIT) in reduction of risk factors constituting metabolic syndrome.

The secondary objective is to compare the efficacy of traditional moderate training (today's guideline) and amount of aerobic interval training (1-AIT vs. 4-AIT) in improving aerobic capacity, cardiovascular function, skeletal muscle contractile function, skeletal muscle energy metabolism, left ventricle systolic and diastolic function at rest and right ventricular function.

The investigators hypothesized that aerobic interval training would reverse features of the metabolic syndrome more than traditional training.

This study describes a randomized multicenter clinical trial designed to test the hypothesis that a 16-week program, with one year follow up of vigorously exercise defined from today's guidelines (performed as 4-AIT (4x4min aerobe interval training)) yields larger beneficial effects in reducing risk factors constituting the metabolic syndrome than continuously moderate intensity exercise (CME) defined from today's guidelines.

Furthermore, the importance of the amount of aerobic interval training remains unclear and it is unknown how little "one can get away with" and still obtain substantial beneficial cardiovascular effects. Therefore, the investigators will also determine whether one bout of aerobe interval training (AIT) - 1-AIT = 1x4min aerobe interval training, can give beneficial effects compared to 4-AIT and CME.

Evaluation criteria are risk factors constituting metabolic syndrome, aerobic capacity measured as peak oxygen uptake and compliance to intervention. Assessments will be made before and after the 16-week program, and at six month, and 1 and 3 years follow-up. According to estimates based on data from previously studies, 3, 4 a total number of 465 patients randomized 1:1:1 to the three interventions gives 80% power to detect an effect of 4-AIT compared to 1-AIT/CME of 51% recovery versus 37% recovery from metabolic syndrome at the 5% significance level.

Inclusion Criteria:

• metabolic syndrome defined according to the IDF-criteria

Exclusion Criteria:

• unstable angina
• recent cardiac infarction (4weeks)
• uncompensated heart failure
• severe valvular illness
• pulmonary disease
• uncontrolled hypertension
• kidney failure
• orthopedic/neurological limitations
• cardiomyopathy
• planned operations during the research period
• reluctant to sign the consent form
• drug or alcohol abuse
• participants in a parallel study