Aerobic exercise is any repetitive activity that you do long enough and hard enough to challenge your heart and lungs. A warm-up simply means 5 to 15 minutes of aerobic exercise at a very easy pace. The American Heart Association recommends 30 minutes or more of aerobic exercise five or more days each week. What exactly does warming up do for you? The term cardio is often used interchangeably with aerobic. To warm up for swimming, swim slowly at first and then pick up the tempo as you're able. To warm up for a run, walk briskly for five to 10 minutes. Here are some examples of warm-up activities: To warm up for a brisk walk, walk slowly for five to 10 minutes. A warm-up warms you up — literally. That can be broken up, though.