Reduced exercise tolerance is one of the hallmarks of COPD. The principal causes for exercise intolerance are ventilatory limitation leading to deconditioning and inactivity. So far it is poorly understood which form of exercise is the most effective in training this condition. The investigators want to study the physiological response to two different training programs (High intensity aerobe interval training and moderate continuous aerobe training)with special focus on cardiac and skeletal muscle adaptions

Reduced exercise tolerance is one of the hallmarks of COPD and The principal causes for exercise intolerance are ventilatory limitation leading to deconditioning and inactivity. However the weak correlation between exercise capacity and FEV1 implies that other factors than reduced pulmonary function contributes to this impairment . Several studies have found changes in skeletal muscle, with fibre shift, increased oxidative stress, increased inflammatory cytokines and impaired mitochondrial function, suggesting a lower limb dysfunction

Numerous exercise studies in COPD patients have shown physiological and physiological benefits of training and endurance training is now regarded as an important part in pulmonary rehabilitation. It is still uncertain what type of endurance training that is most favourable for COPD patients.

In patients with heart failure and metabolic syndrome aerobe interval exercise have be shown to be superior in improving aerobic capacity and cardiac function

We therefore want conduct a study comparing training effects in patients with moderate to severe COPD, that participated in an identical training program that in HF and metabolic syndrome patients gave significant improvement in aerobic capacity, cardiac function and skeletal muscle function.

Patients will therefore be assigned to either 4x4 minutes high intensity interval treadmill exercise or continuous moderate intensity treadmill exercise 3 times pr week for 12 weeks. Aerobic capacity and work economy, pulmonary,cardiac and skeletal muscle function before and after the exercise training will be measured.

Inclusion Criteria:

• COPD with FEV1 25-60 % of exp , FEV1%FVC<70 %. Age 45-80 years

Exclusion Criteria:

• Heart failure
• symptomatic coronary artery disease
• cancer
• alcohol and drug abuse
• severe mental illness
• Lower respiratory infection last 4 weeks
• participation in exercise- or lung rehabilitation program last 3 months.
• oral steroid use