Nothing could be further from the truth. One of the biggest benefits aerobic exercise has to offer is its positive effect on the immune system. Leukocytes help fight any invading foreign bodies that may cause sickness, helping the person to stay healthy. Exercise experts all agree that you need to sustain aerobic activity for a least 20 minutes a session, two to three times a week, at an appropriate percentage of your maximum heart rate, to see any benefits. Whether you jog on a treadmill or use a Stairmaster, here is a way you can monitor your intensity.
Intensity is the key to aerobic exercise.
Inability to reach your appropriate intensity levels will leave you with only minimal immune benefits. On the other hand, going beyond your appropriate intensity levels will leave you with a drop in your immune system. So it's up to the individual to find a happy medium. Always challenge yourself, but progress slowly. To find out if your body is maintaining its BCM, you will need to get it measured.