Most experts recommend at least 20 minutes of aerobic exercise at least 3 times a week to get started. During the aerobic exercise period, you should get your heart rate up and keep moving.
It may take you a while to build to this amount of time, so don't get discouraged. If you don't have large blocks of time, you may want to split your exercise period into 2 or 3 shorter sessions of at least 10 to 12 minutes. You'll still get all the benefits.
It's a good idea to begin your exercise routine with a warm-up and end with a cooldown. Warm-ups include gentle stretching and strengthening exercises and a gradual increase in your activity level. Warming up gently stretches the muscles and brings blood to the muscles and joints, making them ready for exercise. It also prepares your heart and lungs for more vigorous exercise. Your warm-up routine will vary with the type of activity you choose. For instance, if you've chosen walking, walk at an easy pace for a few minutes, then gently stretch your leg muscles and tendons. Then you'll be ready to pick up the pace for your aerobic exercise time. In most cases, the warm-up period should last 5 to 15 minutes.
End your exercise session with a 5- to 10-minute cooldown period. This allows your body to relax. Your heart rate returns to normal. Your body cools down. Your muscles relax and stretch out. At the end of your aerobic period, continue exercising slowly for 3 to 5 minutes. Then do a few gentle stretching exercises.