The length of time you should be exercising will vary according to the intensity of your exercise.
If you are doing low intensity exercise, walking for instance, you should be exercising for 45 minutes to an hour.
Kick it up to fast paced walking or jogging and you can figure your exercise periods should be about 30 minutes to 45 minutes. Go for the 45 minutes if losing weight is a goal.
Now if you do high intensity exercise, for instance, sprinting for 15 seconds, followed by jogging for 45 seconds, you can benefit greatly working out about 20 minutes. The sprinting times and the jogging times can vary, but you will want to work your way up to about 8 sprints.
You can get a lot more detailed help by going to Exercise Tips Digest
