For quite some time, researchers believed that the tortoise approach of slow and stead truly won the fat-burning race. Working at 65-70 percent of your maximum heart rate (MHR) was typically what was considered to be the ideal "fat-burning zone" (as evidenced by the fact that this very information still appears on some pieces of cardio equipment).

However, this school of thought has been challenged by a number of newer studies, and a growing number of people now subscribe to the idea that shorter, high-intensity interval workouts are much more effective at stripping away fat.

Researchers from Cornell University found that high-intensity intervals burn 30-percent more calories per workout than longer, low- to moderate-intensity sessions. And, a separate study, appearing in the American Journal of Clinical Nutrition, revealed that men who completed 20 weeks of interval training lost nine times more fat than men who followed a more traditional endurance program.

The takeaway? Start ramping up your workout. Try running (or any other form of cardiovascular exercise) for short bursts at a very difficult pace, followed by a minute or two of low-intensity movement. Repeat this process several times for maximum results.