Traditionally, continuous, moderate-intensity cardio -- such as walking, running, cycling and swimming -- were thought to be the most effective modes for you to lose weight. However, the increasingly popular high-intensity interval training may be even more effective for losing abdominal fat. Reducing abdominal fat is particularly beneficial, as it is associated with greater risk of cardiovascular and metabolic disease.
Interval training -- intense bouts of exercise lasting from 10 seconds to four minutes, interspersed with recovery periods -- requires less exercise time to achieve results. In the 2008 "International Journal of Obesity" study, the interval group cycled for a total of 20 minutes, which included a warm-up, a cool-down, and 30 cycles of eight-second sprints with 12-second recoveries on a cycle ergometer. The group doing continuous exercise cycled for 40 minutes at a moderate intensity. Although the first group exercised for half of the time, they lost more abdominal fat than their continuous-exercise counterparts, making the interval training a more time-efficient exercise.
Interval training may contribute to more fat loss by suppressing appetite. Although more research on the long-term effects of intense exercise on appetite-related hormones is needed, one study in the journal "Medicina Sportiva" shows high-intensity -- but not low-intensity -- exercise to suppress appetite for a short period following the workout. Therefore, high-intensity exercise may reduce the likelihood that you overcompensate for the calories you burn in your workout by eating more.
Doing cardio at the same intensity week after week will cause your body to burn fewer calories doing the same exercise, and abdominal fat losses may be stalled as well. However, interval training has many inherent options -- you can change the duration of each high-intensity bout or the amount of recovery time between bouts, or you can do your high-intensity bouts on an incline if you are running or cycling. This variety will not only challenge your body, but it will keep your workouts from getting monotonous and therefore make it more likely that you'll exercise consistently.
Although the studies above show interval training to be effective for abdominal fat loss, you should limit interval training to two times per week. More frequent sessions will not allow enough recovery, and you will not be able to achieve a sufficiently high intensity, diminishing the effectiveness of the workout. Studies in individuals with cardiovascular and pulmonary diseases have shown high-intensity interval training to be effective and safe for these populations; however, if you have any health condition or are prone to musculoskeletal injury, you should begin interval training conservatively and consider consulting an exercise professional or doctor for further advice.