High Intensity Interval Training and Skeletal Muscle Insulin Sensitivity

Inclusion Criteria: * Signed informed consent * Age 45 - 75 years old * Overweight to obese (BMI =\> 27kg/m2) * Sedentary - subjects do not perform any regular physical activity weekly(\<3 times per week, \<150 min/week). Exclusion Criteria: * Unstable body weight (weight gain or loss \> 3 kg in the past three months) * Participation in an intensive weight-loss program or in vigorous exercise program during the last year before starting the study. * HbA1c \> 6.5% and glucose clearance rate \>350 ml/kg/min (by OGTT). * Previously diagnosed with type 2 diabetes * Active cardiovascular disease. This will be determined by the questionnaires and by screening on medication. * Use of beta-blockers * Anticoagulant therapy * Systolic blood pressure \>160 mmHg or diastolic blood pressure \>100 mmHg * Abuse of alcohol (\> 3 units (1 unit = 10 gr ethanol) per day) * Any contra-indication to Magnetic Resonance Imaging (MRI) scanning * Participation in another biomedical study within 1 month before the first study visit, which may interfere with the outcomes of the present study. * Use of any medication affecting the glucose homeostasis and whole body metabolism or diseases that may significantly interfere with the main aim of the study. * Chronic renal dysfunction (creatinine \>2 increased (normal value 64-104 µmol/l) * Subjects who do not want to be informed about unexpected medical findings during the screening / study, or do not wish that their physician is informed, cannot participate in the study. * Subjects will be included only when the dependent medical doctor of this study approves participation after evaluating all data obtained during the screening.