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Running and jogging is a great steady-state cardio exercise to burn fat.  If you can jog fast or run, you'll burn more calories and help decrease body fat.  In general, you can burn about 100 calories per mile when you're running.  In addition, running is a great exercise for cardiovascular health.  If you're not a runner, start slow.  You can start with jogging a mile first and slowly increase your distance or pace over the course of several weeks. Spin classes and high intensity biking is another great exercise that will burn large amounts of calories and fat.  Spin class is done indoors on a stationary bike.  You can control your speed and resistance on the bike.  However, the harder you work and the faster you pedal, the better fat burn you'll get. If you haven't tried a spin class before, it's important to take your first few classes slowly.  They are very high intensity and it may take a few weeks to bring up your fitness levels. Spin is also generally done inside in a closed room.  You can get very hot and sweat a lot.  It's important to re-hydrate continually throughout a spin class. Step aerobics is a another great cardio class to help you burn calories and fat.  It's particularly effective due to it's focus on your legs and glutes.  These large muscle groups make you work up a sweat causing you to burn calories and fat.  You may burn up to 400 calories in 30 minutes if you work out at your hardest intensity. Again, if you haven't done a step aerobics class, start slowly.  Use a smaller step and any modifications to movements that are too difficult for you.  Over time, you can use a bigger step or do movements without modifications. Another type of cardio activity is HIIT. This type of cardio burns more calories from fat and also raises your metabolism for about 24 hours after you've completed the workout.  During HIIT you alternate between short bouts of very high-intensity cardio and short bouts of more moderate-intensity cardio.  You do not spend as much time doing HIIT compared to steady state cardio exercises, usually about 20 minutes (with an additional 5 minutes at the beginning and end for a warm up and cool-down). They are intended to be shorter, more vigorous exercises. Studies have shown that there is a close relationship between the intensity of cardio exercises and the reduction of stomach fat.  Participating in HIIT may be very effective for reducing abdominal fat.
Run or jog. Do a spin class or include high intensity biking. Step aerobics. Do high-intensity interval training (HIIT).