If I meditate, do I still need to exercise?
Yes. Meditation is no substitute for physical exercise. They are complementary: meditation exercises your mind while physical exercise conditions your body. So keep up with your regular exercise.
You can try a form of walking meditation as an alternate choice of exercise. Walk at least three times a week, each time for about half an hour. If possible, try to walk before 10 a.m., before the sun is too hot. The sunlight provides excellent yang energy for you. Walk leisurely, and keep your head clear by using the Vajra Sword Contemplation Method.