Bodybuilders and trainers have always gone with the steady-state cardio method, meaning that using low to moderate intensity exercise performed at 60-70% of maximum heart rate (MHR), to lose body fat without losing muscle. But the latest research indicates that a new method may be better, and less time consuming.
The HIIT training method involves short intervals of high intensity training. With a short exercise with around 90% MHR, followed by intervals of slower paced active recovery. Early research on the HIIT method showed that it was superior to the steady state method of cardio for losing fat. Researchers found that despite the fact that it takes less time, you actually burn more fat. One of the earliest studies was done by researchers at Laval University (Quebec, Canada), they kept it basic by using two groups in a months-long experiment. One group followed a 15 week program using HIIT while the other perfomed only steady state cardio for 20 weeks. The steady state group actually burned 15,000 more calories than the HIIT group. But the HIIT group lost significantly more bodyfat.
The most recent study from Australia, reported that a group of females who followed a 20-minute HIIT program consisting of 8 second sprints followed by 12 seconds of rest, lost 6 times more bodyfat than a group that followed a steady state cardio program for 40 minutes at 60% MHR!
So how does HIIT work so well while occupying less of your time? Because the intensity is higher, more calories are needed to repair the damage done during the exercises. All research performed on subjects using the HIIT method found that these groups burned an average of 10% more calories in the 24 hours following the exercise than the normal groups.
Research also confirmed that HIIT enhances the metabolic machinery in muscle cells that promotes fat-burning and blunts fat production. The Laval University also discovered that the HIIT subjects had significantly higher marks for fat oxidation in the muscle cells than those in the steady state group.
If you want to give HIIT a try, here's a sample Treadmill routine. Remember, the HIIT method can be done on a track, on a treadmill, on a bike … just play around until you find what groove works best for you.