Aerobic exercise is the kind that increases your heart rate and makes you huff and puff. It promotes general fitness, conditions your heart and respiratory system, and increases stamina. It also tones your nervous and immune systems, reduces stress, increases the flow of oxygen throughout the body, and gives you a sense of strength and well-being. For optimum cardiovascular fitness, I recommend exercising every day. Aim toward at least 30 minutes five times a week. It need not be in one continuous session. Ideally, your daily routine should also include plenty of aerobic activity, such as brisk walking, housework, gardening, and so on.
I am a great proponent of walking for fitness. Sustained walking - especially uphill walking and brisk walking - can give an overall better workout than running or exercising intensely on aerobic machines. Walking has the advantage of not requiring any equipment and carrying the least risk of injury of any aerobic exercise. Use good posture, swing your arms, and keep a good pace. Three miles should take about 45 minutes. I recommend running shoes for this activity - ones with well-cushioned insoles.
Walking with poles is especially beneficial for those with early-to-advanced degenerative joint disease and those rehabilitating from knee surgery. It also improves balance when walking over uneven terrain, thus helping to prevent slips, sprains and other injuries.
Fitness poles aren't the same as walking sticks, which are more common in Europe than in the U.S. although they've become more popular here in recent years. Fitness poles take some getting used to - for maximum benefit you have to learn how to use them properly. Always start with two poles, one in each hand. Poles are not meant to be dragged on the ground or held in the hand like a walking stick. Start slowly and coordinate the pole plant with your stride. Plant them lightly with arm extended and push off forcefully with each stride to get an excellent workout. Remember, plant the pole opposite to the foot that hits the ground (e.g., plant the right pole as the left heel hits the ground). Be patient; it takes practice to make the movements smooth, and don't worry about looks from passersby: the health benefits outweigh the small embarrassment of looking like you're trying to cross country ski without the benefit of snow.
Specific forms of exercise have their own benefits. Swimming is great for the joints, a balanced muscular workout, and relaxation. Cycling builds knee muscles and can provide a feeling of exhilaration. Dancing is one of the best aerobic activities of all, because it's fun, never boring, and provides a thorough workout.
Once you have developed good habits of regular exercise, begin to add stretching, muscle toning, and strengthening to your routine. Yoga is a great way to stretch, improve flexibility, and experience deep relaxation. Breathing exercises, meditation, and other forms of relaxation are important to help neutralize stress.
Personally, I walk whenever possible. I use a Stair Master occasionally, and go mountain biking in the desert. I also swim and do some weight training. I dance, jump rope, run, and hike - and mix all of these up.
I don't think that calorie burning is the best guide to how much exercise you should do. If your weight is stable, think in terms of overall cardiovascular fitness, strength, and flexibility. Vary your workout to keep it interesting. And, above all, have fun!