**According to the Mayo Clinic, a 240-pound person burns 796 calories during each hour of high impact aerobics, which means that it takes 4.4 hours of such exercise to burn 3,500 calories.** One pound of fat is equivalent to 3,500 calories.

The Mayo Clinic notes that the number of calories a person burns in an hour of exercise depends on the individual's weight and the type of exercise. A 160-pound person burns 533 calories in an hour of high impact aerobics, needing 6.5 hours of such exercise to burn 3,500 calories, two more hours than a 240-pound person needs. A 240-pound person takes just over eight hours of leisurely bicycling to burn 3,500 calories, while a 160-pound person takes almost 12 hours.