If you exercise, you can reply "I am exercising, but I am not doing high-intensity fitness programs" and explain it according to your actual situation like this. If you don't exercise, you can reply "No, I'm usually busy, and I feel like I don't have time to exercise" and so on.
Fitness is a kind of exercise, such as all kinds of unarmed aerobics, rhythmic gymnastics, rhythmic gymnastics, and all kinds of self-resistance movements. Gymnastics and yoga can enhance strength and flexibility, increase endurance, and improve the ability to coordinate and control all parts of the body, thus making the body strong.