When it comes to the primitive fight or flight response, choose the latter. Flee to the gym after work, outside for a morning walk, to the tennis court with a friend -- any kind of exercise will do. Regular aerobic (heart-pumping) exercise is particularly effective at controlling stress, and it improves your physical as well as your emotional health. There's no need to go on an Olympic training schedule to benefit. Health experts recommend 30 to 60 minutes of aerobic exercise three to four times a week. You can take an aerobics class, but aerobic exercise comes in many fun forms: walking, hiking, jogging, dancing, bicycling, swimming, cross-country skiing, racquet sports, and martial arts.Many people choose walking as their primary or only aerobic exercise because it's free, easy, and flexible. You can walk almost anywhere, you can set and adjust the pace, you can choose solitude or company, and you don't have to commit a set amount of time. Stressed at work? Walk briskly around the building. Tired out by tragic events in the news? Take a walk through the neighborhood. Need to clear your mind or develop new ideas? A walk works like drain cleaner, allowing thoughts to flow more easily. To reap the long-term rewards of this exercise, health experts suggest walking three times a week for 20 to 30 minutes, gradually picking up the pace, time, and frequency. You can supplement by walking to the grocery store, using the stairs instead of the elevator, parking at the far end of the shopping mall, or exiting the bus one stop early and walking the difference. Gardening, golfing (sans golf cart), and walking the dog can also be a part of your fitness and de-stressing program.Non-aerobic activities also help you reduce stress, develop muscle tone, and increase flexibility.The secret to maintaining an exercise program is to do what you enjoy -- and do it regularly.