Endurance Training Versus High Intensity Interval Training

Cardio is probably the least understood form of exercise while being the one most often used in the gym. When I walk in to a gym especially at busy times, all of the treadmills and ellipticals are nearly full with people busily pumping along at a steady pace.  Sometimes their pace is so slow I will see them reading!  And the free weights and weight machines are mostly empty.
There are 2 contrasting ways one can perform cardiovascular exercise: endurance training / steady-state cardio (slow to medium speed at a long duration), or HIIT  (high intensity interval training), high speed at a short duration.  This past weekend I attended a certification course for metabolic training.  I learned the science behind how short bursts of high intensity exercise for 20 minutes can be more effective than 60 minutes of steady-state cardio.  Now, understanding that the instructor was very strong in his beliefs, I also came home to do my own research about its effectiveness.  But after my research, I fully agree with my instructor.  It has been tested and proved that short, intense workouts provide improved athletic capacity and condition, improved glucose metabolism, and improved fat burning.
Let’s first discuss steady-state cardio or endurance training.  During a 45-60 minute workout on a cardio machine, one will breath heavily and work up a sweat, so it is evident that they are working fairly hard.  Have you seen a marathon runner with a pot belly?  The body clearly is burning fat.  There are plenty of health benefits from running.  But along with consuming fat, the body consumes protein (muscle) in order to keep the body fueled for a lengthy training session.  If your goal is to look lean and toned for the beach this summer, you want a bit of muscle.  This makes the idea of jogging an hour on the treadmill or an elliptical seem fairly counter-intuitive.
HIIT is considered to be an excellent way to maximize a workout that is limited on time.  A HIIT session consists of a warmup period, followed by six to ten repetitions of high intensity exercise, separated by medium intensity exercise, and ending with a period of cool down exercise.  The high intensity exercise should be done at near maximum intensity, about 85-90% of your maximum heart rate.  You should feel exhausted and you should have a hard time talking.  The medium exercise should be about 50% of your maximum heart rate.  The number of repetitions and length of each depends on the exercise.  I prefer timed exercises.  2:1 ratio of work to recovery periods, for example, 30–40 seconds of hard sprinting alternated with 15–20 seconds of jogging or walking or 30-40 seconds of plyometric box jumps followed by squat jumps.  The goal is to do at least six cycles, and to have the entire HIIT session last at least fifteen to twenty minutes.
Let’s talk about the afterburn effect.  This refers to how your exercise can affect your calorie burn even after you’re finished working out.  I recently experimented with the Body Bugg.  It is one of the most accurate tools out there to calculate your calorie burn.  I did steady-state cardio on the elliptical for 60 minutes one day.  The elliptical showed I burned 600 calories.  The Body Bugg showed I burned about 275.   After the workout, I continued to burn minimal calories for the following hour.  The following day I performed a 25 minute HIIT workout.  I burned about 350 calories and about 500 calories for the following hour.  That day I burned many more calories in total as compared to the steady-state cardio day.
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Anyway, what does all of this mean?  Bottom line, mix it up.  If you are an intermediate to advanced exerciser and your goals are weight loss and toning quickly, don’t waste precious time doing ONLY steady-state cardio (or any other form of low-to-moderate intensity exercise).  It means you can invest 25 minutes and get the same (or better) fat burning results.  With this said, you could spend 105 minutes of exercise per week and get the same level of results as when you were working out more than twice that amount.  On the off days of HIIT, I suggest longer exercise sessions (you can still do endurance training) and incorporate some weight lifting.  A nice balance would be to perform interval training alternating free weights with short bursts of moderate intensity cardio.
And one last thing – look at the picture above.  The picture on the left is a marathon runner (moderate intensity, long duration) and the picture on the right is a sprinter (high intensity, short duration).  They have very different types of muscle fibers.  The marathon runner has mostly slow twitch muscle fibers and would not have the force to propel his body forward quickly.  The sprinter has mostly fast twitch muscle fibers and would not last running long distances.  Now, I know there is a big difference in age here, but which would you rather look like?