Individuals who participate in regular physical exercise possess a lower prevalence of cardiovascular risk factors such as hypertension, type 2 diabetes, obesity and hypercholesterolemia, and aerobic exercise is therefore considered an important adjuvant therapy in risk factor modification and to promote health.

The main focus of the present study is therefore to detect how rapid it is possible to increase aerobic capacity with interval running exercise.

The hypothesis is that it is possible to improve maximal oxygen uptake faster when increasing training frequency. The total gain in maximal oxygen uptake will however be the same between the two groups when they have performed the same amount of training

We will perform aerobic interval training at an intensity of 90-95% of maximum heart rate in healthy individuals. The subjects will be randomly assigned to carry out a total of 24 exercise-sessions, either at 3 times per week or 8 times per week.

The two groups will carry out 24 training sessions before 8 weeks of detraining will provide how rapidly aerobic capacity is lost due to inactivity. After the detraining period a retraining phase is introduced to detect if improvements in aerobic capacity occur more rapidly compared to before the first training period

The subjects will be tested for oxygen uptake, pumping capacity of the heart, blood volume, skeletal muscle enzyme activity, endothelial function.

Inclusion Criteria:

• BMI<27, non-smokers, train less that 1-2 times per week, VO2max <60 for male and <50 for female.

Exclusion Criteria:

• Hypertension, diabetes and cardiovascular disease.