The real ‘Fat Burn’ Zone

INDIANAPOLIS (WISH) – You see the “Fat Burn Zone” as a setting on pieces of cardio equipment, but it doesn’t mean what you think.

“It’s a little misleading in that sense and I think it gives the public a little bit of a false sense of security about what they’re doing,” says Dr. Tony Kaleth, an exercise physiologist, professor, researcher and marathoner.

The “Fat Burn Zone” — as it’s listed on cardio equipment — is simply a lower intensity range where your body burns the highest percentage of fat, but not the most calories of any exercise.

“It really takes the higher intensity exercise to burn more calories,” says Kaleth.

High intensity exercise takes you to maximum effort very quickly, for example, Crossfit with its explosive moves, or basketball with its sprints and physical drives. Running can also be high intensity when the pace is swift and difficult to sustain.

“There are numerous variations of programs that incorporate both strength and aerobic training into one workout–like Insanity or P90X,” says Kaleth. “These programs typically involve alternating muscle group exercises with little rest between sets.”

How your body chooses what to burn

Our bodies primarily use a combination of carbohydrates and fat as sources of energy. At rest, we use a greater percentage of fat compared to carbohydrate. As we transition from rest to light intensity exercise, we begin to burn calories at a faster rate to fuel the working muscles, but still primarily rely on fat as an energy source. This light intensity activity is what constitutes the “Fat Burn” zone on cardio equipment.

As we begin to exercise at higher intensities, the exercising muscles require much greater amounts of energy in order to sustain the work being performed. Because we can’t break down stored fat quickly enough to feed the muscles at higher intensities, our bodies gradually shift to a more readily available form of energy–carbohydrate. This shift to more carbohydrate utilization continues up until maximal exercise where we primarily rely on carbohydrate as the primary energy source.

“You can do low-to-moderate intensity activities and gain a lot of health benefits such as reducing blood pressure or improving lipid profile,” says Kaleth. “For caloric expenditure and weight loss, your goals are going to have to be a little bit higher.”

The True “Fat Burn Zone”

A study in the journal Metabolism compared 20 weeks of aerobic training with only 15 weeks of High Intensity Interval Training (HIIT) in which participants did 15 sprints for 30 seconds and lost nine times more body fat than the aerobic group. They also lost 12 percent more visceral belly fat than the aerobic group.

A study in the International Journal of Obesity compared the effect of 15 weeks of HIIT up against aerobic exercise. The HIIT resulted in significant decreases in overall fat mass of 3.3 pounds, while the aerobic exercise group had a fat gain of 1 pound on average. The HIIT group also had a significant 9.5 percent decrease in belly fat, whereas the aerobic group increased belly fat by 10.5 percent at the end of the study.

How to “up the ante”

Dr. Kaleth points out there are a number of ways to incorporate high intensity intervals into your exercise routine. Intervals can be done indoors or outdoors and can involve walking, jogging, running, elliptical, cycling, stepping, skating, weight lifting, etc.

How many days per week you perform intervals will depend on your current fitness level, injury history, and health and fitness goals. In general, to reduce the potential for injury, particularly for beginners, Kaleth suggests interval training should be limited to no more than two to three sessions per week on non-consecutive days.

Interval training programs are inherently designed to complete a large volume of activity in a short amount of time. Individual exercises may range from 10 seconds to several minutes, followed by a rest period. This pattern is typically repeated several times. In total, the duration of an interval training session will vary considerably, lasting for as little as 15 minutes to as long as 60 minutes.

“Primarily those people just getting started with an exercise program need to be more careful about engaging in high intensity exercises,” says Kaleth. “Older adults need to be careful, and people with heart disease should talk to their doctor before doing these types of activities. For the general public, its a good idea to have a good solid exercise foundation before trying anything like this.”

Dr. Kaleth’s Sample Interval Training Programs

Beginners: Begin each session with a 10-minute brisk walk. Run at a brisk pace for 1 minute, then walk quickly for 1:30. Repeat the cycle six times each session, for three sessions in the first week. During the second week, run for 1:30 then rest for two minutes. Repeat four to five times. Continue increasing the run time and rest time for the first few weeks.

Have a dog? Next time you take Fido for a walk, try alternating 30 seconds of walking with 30 seconds of jogging. Or, take Fido to the park and throw around his favorite toy. He’ll chase it and you can chase him! Both you and your pet will gain some valuable benefits, plus have a blast doing it!

For higher fit individuals or those with specific exercise training goals in mind, consider incorporating sprint interval training into your workouts one to two days per week. After a 10-minute warm-up, alternate 10 seconds of walking with 20 seconds of sprinting for 15 minutes. Adjust the walk and/or run times up or down depending on your fitness level. Note: These intervals also could be done on a different piece of aerobic equipment, (e.g. cycle, elliptical, stair climber, rowing machine, etc.)

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