You'll burn more fat when you do interval runs.
Interval training, which is an exercise routine in which you switch between a high-burst, high-cardio workout and a slower pace, can burn more fat than simply keeping a consistent pace throughout your workout. Running may burn more calories, but the switch between slow and fast paces can actually induce your body to burn more fat. Before switching to this type of training, make sure it lines up with the goals of your workout.
When you want to try interval training, start slowly and build yourself up to a greater number of high-intensity segments. The exact speed isn't important, as long as you are alternating between a walk and a high-intensity run that makes you breathe harder and your heart beat faster. Your goal is to eventually be able to sprint for 60 to 70 seconds at a time, with a one- to two-minute walk in between. But when you're first starting out, you may need to limit yourself to 10 to 20 seconds of sprinting at a time. Each interval session should be about 25 to 30 minutes long, only done every other day at the most so your body has time to recover.
How It Works
High-intensity interval training increases the amount of fat you burn because you are doing both aerobic and anaerobic exercise. Interval training helps you lose more subcutaneous fat and abdominal fat than when you exercise at a steady pace. This is partially because the interval exercise causes the body to release more adrenaline and human growth hormone, which burn excessive fat. In addition, an effect called excess-post exercise oxygen consumption occurs up to 24 hours after interval training. This means your body needs to burn more oxygen to catch up with what it lost, which causes your body to burn more calories from fat.
Interval training isn't without risks, though. If you're out of shape and just getting back to exercising, slowly work to build up your cardio fitness before you start doing high-intensity workouts. If you have a chronic health condition, such as heart problems, the high-intensity part might not be beneficial and you should ask your doctor first before proceeding.
Alternating between walking and running fast when you're working out can also bring other benefits that enhance the fat-burning advantages. Your heart health will improve, allowing you to work out for longer periods at a time and keep up the high-intensity portions longer. The short rest periods improve your body's ability to recover from a workout, which means that if you want, you'll need shorter periods of rest in between hard workouts. You'll also increase your body's ability to handle lactic acid buildup in your muscles, which is what causes your muscles to feel sore the day after a workout.