High Intensity Interval Training: Super Quick, Super Effective

If you want to lose weight and maximize your cardiovascular health, what is the best kind of exercise? 60-minute sessions of aerobic exercise in the “fat burning heart rate zone” right?  Wrong!  This has been a commonly accepted exercise routine for years and while it has it’s benefits, it’s simply not the most effective or efficient. Lengthy aerobic sessions often lead to frustration because it’s difficult to fit that much time into your daily routine and they often don’t yield the results they promise.

Exercise and Metabolism

The primary problem with traditional cardio exercise is that once you are done with the exercise the calorie burning is done as well. There are other kinds of exercises that actually keep metabolism boosted long after the exercise session has ended. These exercises can also help maintain and build muscle. I am referring to high intensity interval training (HIIT).

High Intensity Interval Training (HIIT)

I am a huge proponent of HIIT, recommend it to most of my patients, and make it a regular part of my own fitness routine. HIIT has been around for a while yet it is still unfamiliar to many. It has an enormous body of research to back it up along with real world results.

There are many different types of HIIT programs but one thing they all have in common is short bursts of maximum intensity alternated with short resting phases. A classic example is to sprint for 30 seconds and rest or walk for one minute, and repeat this for about 8 cycles.

Anaerobic vs. Aerobic

HIIT puts the body into an anaerobic rather than an aerobic state. During anaerobic exercise we burn glucose and glycogen from the muscles for fuel.  During aerobic exercise we burn fat as the primary energy source.  You may ask, “why wouldn’t I want to burn fat during a workout?”  Simply put, when you primarily burn fat during exercise the body thinks that it needs to store more fat as fuel for the next workout, which results in greater difficulty losing weight (one of the purposes for exercising in the first place). But when you burn glucose and glycogen as the primary fuel the body instead learns to rely on them as a source of energy during exercise. As a result, energy will be stored in the form of glycogen in the muscles rather than as fat. Consequently HIIT has been proven to be more effective than steady state cardio for weight loss.

Furthermore, after doing HIIT the body’s metabolism remains elevated for 2-4 hours after the workout has ended. This leads to burning more total calories, which is probably the single most important factor for weight loss. This post-workout calorie burning is likely due to the extra effort required by the body to repair the micro-damage done to the muscles during exercise, much like that of training with heavy weights. Muscle damage of this type leads to increased strength and muscle size after the muscles have repaired themselves.

Steady-state Cardio and Muscle Loss

Most people exercise with the intent to lose or maintain their weight, however, the amount of total weight loss isn’t necessarily the best gauge for progress. During lengthy, extended periods of steady-state cardio exercise often both muscle and fat are lost. This in effect makes it more difficult to maintain weight in the long run and can negatively affect future health as well because not only does it not build muscle, in some cases it even leads to muscle loss. For example, think of the physique of Olympic marathon runners versus sprinters. The former (first image) are very lean and have relatively low muscle mass, while the latter (bottom image) are also lean but tend to have substantially more muscle. Granted these are people who are training for a specific purpose to gain a competitive advantage in their sport, but it demonstrates the stark contrast in physique produced by the two types of exercise.  However, if your aim is good health, more muscle is better.

Anaerobic Exercise = Muscle Building = Healthy Aging

One of the greatest advantages of HIIT is that as an anaerobic exercise it leads to muscle building and the more muscle mass your body has the more calories it will burn just to stay alive – this effectively increases your resting metabolic rate. In turn, it also helps maintain the muscle you already have and builds upon that foundation. By the time we reach about 40 years old we are continually losing muscle as we age leading to a plethora of issues such as weakness, poor balance, increased risk of diabetes, and high blood pressure making us more likely to need assisted care or nursing homes in old age. The more muscle we can build and maintain the less likely we are to face an array health problems later in life. Building muscle ought to be one of our primary to avoid these pitfalls.

Another advantage of HIIT is that it only needs to be done for short periods of time (about 4-20 minutes depending on the particular program), which means there is much less wear and tear on joints (e.g. knees, hips, ankles, etc.).

Health Complications Associated With Traditional Cardio Exercise

Multiple studies have shown that long bouts of traditional cardio exercise can actually weaken the immune system. Even worse, a study from 2013 showed that cardio/aerobic exercise shrinks telomeres. Telomeres are caps at the end of each DNA strand that protect our chromosomes and are highly associated with aging and disease.  The longer they are the better (decreased risk of cancer, heart disease, stroke, etc.). You can think of them like a fuse on a stick of dynamite. The longer the fuse the more time before it explodes.  On the other hand, multiple studies have shown that HIIT increases telomere length.

Here are some studies showing the specific benefits of HIIT

• One of the first studies on HIIT from Laval University in Quebec monitored two groups of participants. One group did 15 weeks of a HIIT program and the other did steady state training (lengthy cardio sessions) for 20 weeks. The group that did HIIT burned 15,000 more calories than the steady state group and in five weeks less time!

• Another Canadian study compared the fat-loss effects of interval training versus a traditional, cardio regimen and found that those who performed intervals lost more body fat.

• In a recent study from Australia a group of women who followed a 20 minute HIIT program consisting of 8 second sprints followed by 12 seconds of rest lost six times more body-fat than the group that did a 40 minute cardio program at 60% constant intensity.

• In 2007 a study from Florida State University found that study participants who did HIIT burned about 10% more calories during the 24 hours following exercise than did he steady-state cardio group.

• A Danish study from 2014 observed two groups of diabetics. One group did interval walking, one did continuous walking and the third group did nothing. The group that did interval walking significantly improved their HbA1c (a measurement for blood glucose regulation), and both the steady state and no walking groups had no change in their HbA1c. In other words steady state walking wasn’t any better for their blood sugar than doing nothing!

There are countless HIIT routines but here are a few to consider:

• Three minute warm up; 30 second sprint, 90 seconds walk; repeat 7 more times for about a 20 minute period.
• 30 seconds brisk walk, 30 second sprint; repeat 7 more times for 8 minutes total.
• Swim at full speed for one lap, rest for 30-60 seconds; repeat up to 20 minutes.
• 20 second sprint, 10 seconds rest; repeat 7 more times for 4 minutes total. This is an example of the Tabata Method which was developed by the Japanese Dr. Izumi Tabata. Studies have shown this very short duration HIIT method to be highly beneficial in improving cardio fitness and insulin sensitivity. This is a great example of how high intensity packed into a short period of time can be hugely beneficial.

During the high intensity portion the key is to push yourself to your maximum effort. This means it should be difficult to breath and talk. You may even feel a muscle “burn.”

This is not to say that all you should do is HIIT. It is important to keep your overall fitness regimen well rounded and include the following:

• Strength training: build muscle and strength, increase metabolism, stabilize joints, improve posture, etc.
• Stretching: improve flexibility, decrease risk of injury, improved circulation, improve posture, etc.
• Core exercises: much of this can be accomplished as a part of strength training and stretching, especially if strength training regimen includes compound exercises such as squats, deadlifts and presses.
• Traditional steady state cardio: Yes, I have been critical, but while it’s not great for building muscle or burning fat, when done in moderation it increases endurance, and overall cardiovascular health. It is particularly effective at lowering resting heart rate, which is a good marker of physical fitness.