How long should you exercise for?

30 minutes: Exercise for 30 minutes minimum for a minimum of 3 times a week. If you get tired with minimal exercise (you can't walk a flat city block, 300 feet or so, or a flight of stairs) without difficulty you should see a doctor. Also, it's always a good idea to talk over an exercise program with a doctor if you have a chronic illness or medical condition.

4 X/wk, 40min each: How much exercise and what type(s) one should do is quite variable, dependent on age, physical condition, weight, medical illnesses, muskuloskeletal problems, conditioning status. In general, start low and build up to goal, both in time and intensity. Would recommend aerobic (treadmill, outdoor walk, elliptical, swim) above amt. Some resistance training also. If some part of body hurts, stop stat.

Depends on person: A good goal is to get about 30 minutes of moderate intensity exercise at least 5 days a week. You should include aerobics, strength training and stretching. Depending on your general condition you may want start slowly with shorter less intense workouts and gradually increase the time and effort. Talk to a doc if you have any health concerns and remember that a healthy diet is important here too.

20-40 minutes: You get most benefit by doing moderate intensity exercise for 20 minutes per day. Avoid exceeding 40 minutes/day.

Depends on Goal...: For overall health shoot for a total of 150 minutes a week, or about 30 minutes a day for 5 days a week, with your pulse about 60% of your max predicted. Studies show you can break this up in other ways but the key is getting your pulse to the desired level before starting the clock. aerobic conditioning, anaerobic conditioning, and other techniques are approached differently.