I have been told that if you raised your heartrate and kept it up for at least 10 minutes then it is enough exercise. Doing anything to raise your heartrate is great, but you need to keep it up for an amount of time to reap any benefit. That's why they say at least 20 to 30 minutes of exercise a day can help. It takes about 10 to get up there, 10 to stay there, and 10 to come down back to where you were - depending on the exercise/activity of course.