High Intensity Interval Training is a method of exercising that utilizes short bursts of maximal effort followed by limited recovery periods. A 2008 study published in “Exercise and Sports Sciences Reviews” reported that just six 15-minute sessions of HIIT can increase muscle, aerobic performance and metabolism. These workouts are usually no longer than 20 minutes, due to their intensity. The ratio of work to recovery can vary, depending on your current level of fitness. For example, you could perform a 30-second work interval followed by a 90-second recovery if you were fairly conditioned. You could increase the challenge by making the work and recovery intervals the same length, or even perform work intervals that are slightly longer than your recoveries.

High Intensity Resistance Training utilizes the same principles as HIIT, but with a focus on resistance-training exercises. Traditionally, many people rest up to several minutes between weight-training exercise sets to allow the body to replenish supplies of adenosine triphosphate and creatine phosphate. While this is important for those training for maximal power and strength, people with fat-burning goals will benefit from shorter rest periods. Limiting rest intervals increases intensity by keeping the calorie burn and heart rate elevated. A 2013 study in the “Journal of Translational Medicine” found that subjects burned significantly more calories after HIRT than traditional resistance training.

Some people have a hard time motivating themselves to work hard enough to achieve the intensity required for significant fat burn. For these folks, high-energy group fitness classes may be an excellent fitness option. Bootcamps, CrossFit, indoor cycling and kickboxing are just a sample of the many group classes available across the country. According to Deborah Feltz, Ph.D., professor of kinesiology at Michigan State University, individuals routinely perform activities better when they are in a group — a phenomenon known as the Köhler effect.

Always talk with your doctor before beginning a new exercise program. High-intensity exercises may not be appropriate for everyone, especially those who are pregnant or who have cardiovascular problems. Always listen to your body during exercise — if at any point you feel dizzy or faint, stop and rest immediately. If you’re new to exercise, ease into high-intensity workouts by slowly increasing the intensity over a period of time. You have to crawl before you can walk.