Can Interval Training help you strip off body fat faster? Learn how adding High Intensity Interval Training (HIIT) into your cardio routine can reap big rewards in strength, power and fat loss.
When most people think of cardio, they think of endless hours on a treadmill, elliptical machine, stair stepper or jogging. But unless you enjoy distance or long-duration cardio (for example, if you are training for a marathon or are a running enthusiast) , many gym-goers dread climbing on that hamster wheel each day in the hopes of burning off that 400 calories and maybe losing a little body fat along the way.
But what if there was a way to burn nearly the same amount of calories in 30 minutes that you do in 60 minutes, stimulate fat burning after your cardio is complete, boost your stamina and endurance, and actually increase lean muscle in the process?
There may be.
It’s called Interval Training — also known as “High Intensity Interval Training” or “HIIT“, for short — and it uses periods of high-intensity cardio coupled with lower-intensity recovery periods in succession to shave time off your cardio workout and possibly more fat off your midsection than long duration cardio. And even more promising, Interval Training seems to do a better job than long-duration cardio of preserving lean tissue (muscle) while still burning fat.
Interval Training: What Is It?
Simply put, Interval Training is a method of cardiovascular training that has you perform the same amount of total work that you would perform in a longer session of cardio, but in a much shorter period of time by increasing the intensity of your workout.
Interval Training is considered an advanced form of training and is popular with everyone from elite Olympic and professional athletes to body builders, fitness enthusiasts and recreational runners. While the technique is advanced, it can be successfully modified to work for beginners as well, provided you are in good health and are free of any cardiovascular disorders that could make the routine unsafe.
Interval Training relies on the principle of rest and recovery to allow your body to do more work in less time. By alternating higher-intensity activity with short rest and recovery periods, you are able to cumulatively do more work in less time. And more work translates into more calories burned in a 30 minute session of cardio than if you did the same duration of cardio at a lower intensity.
Examples of Interval Training
High Intensity Interval Training can be applied to nearly any cardiovascular activity, whether that’s walking, running, rollerblading or biking.
For example, if you are fit and regularly walk as part of your exercise routine, you might incorporate short periods (between 1-2 minutes) of jogging into your walk between lower-intensity periods of walking. If you are less fit, you might simply walk faster for a few minutes, allow yourself to recover and than repeat the higher intensity walking. If you are more highly conditioned, you might add in sprints to your daily run or treadmill work.
The Benefits of High Intensity Interval Training
High Intensity Interval Training has a number of benefits that make it an effective addition to your existing cardiovascular training. These benefits include:
- Burning more calories in less time
- Improved cardiovascular endurance
- Possible increases in whole body fat burning (fat oxidation) versus solid-state cardio
- Reduced risk of Metabolic Syndrome
- Decreased muscle catabolism/increases in lean muscle mass
- Improvements in arterial elasticity
- Reduced boredom with your current cardio routine
Let’s take a closer look at each of these potential benefits, including some of the research behind them.
You Burn More Calories in Less Time with Interval Training
Using Interval Training, you can literally burn the same amount of calories in 30 minutes that you normally might burn in 60 minutes of lower impact, lower-intensity cardio. If you are pressed for time, High Intensity Interval Training can allow you to be more efficient during the time you set aside for cardio and achieve the same effects as longer duration activity.
The key here, however, is to perform the exercise at an intensity level that is sufficient to cumulatively burn an equivalent amount of calories in a shorter period of time. Depending on your level of conditioning, this may or may not be possible.
Higher intensity work is … well … more “intense.” So beginners may not have the stamina to be able to alternate their high and low-intensity periods for a duration that is sufficient to match the calories burned with longer duration — but more moderate — cardio training. If this is the case for you, consider alternating your cardio workout between solid-state exercise and HIIT for the best of both worlds.
Improvements in Cardiovascular Endurance
Interval Training allows you to rapidly increase your cardiovascular endurance and improve something called your VO2 Max – a fancy term that describes how much oxygen your body can transport during exercise or activity. The higher your VO2 Max, the less winded you become during exercise.
VO2 Max is considered the ultimate indicator of a person’s cardiovascular fitness and aerobic capability, and Interval Training can be an extremely effective method for improving VO2 Max, both among beginners and advanced athletes. And because you allow your body to recover after each burst of intense activity, you are able to more comfortably increase your performance without becoming exhausted.
And the research seems to back this up.
A 2005 study conducted by McMaster University in Hamilton, Ontario and published in the Journal of Applied Physiology took a look at eight college-age men and women to see what impact Interval Training would have on their endurance during moderate intensity bicycling. After two weeks of Interval Training, the researchers found that six of the eight research subjects had doubled the amount of time they could bicycle at the same pace before becoming exhausted. The eight exercisers in the control group who did not perform any Interval Training showed no improvement in endurance.
High Intensity Interval Training and Weight Loss and Fat Loss
There is also some evidence that Interval Training may be more effective at burning fat than lower-intensity cardio exercise.
A study by University of Guelph in Ontario and published in the May 2007 issue of the Journal of Applied Physiology took a look at how incorporating bursts of higher intensity activity into low-or-moderate intensity exercise impacts fat burning in the body.
The study had eight women in their early 20s cycle for 10 sets of four minutes of hard riding, followed by two minutes of rest. Over a two week period, they completed seven interval workouts.The researchers found that whole body fat oxidation among the interval trained group increased 36 percent after performing HIIT versus low-intensity or moderate intensity training. Even more noteworthy, these improvements were consistent regardless of the fitness level of the subjects before undertaking the High Intensity Interval Training.
It’s important to note that while these initial findings are certainly encouraging, the study’s lead author and exercise scientist Jason L. Talanian cautions that the group studied was small and that additional research is necessary to validate whether Interval Training can give you a fat burning boost.
Interval Training for Lean Muscle
Distance or long-duration cardio training (generally in excess of 60 minutes) can put you at risk for losing lean tissue or muscle, as the body depletes carbohydrate stores and turns to burning muscle for fuel.
Interval Training, however, seems to discourage muscle catabolism, and may actually encourage muscle anabolism (growth), especially when performing low-volume sprint training or when employing resistance to increase intensity — for example by increasing the incline on a treadmill or the resistance on a stationary bike or elliptical trainer.
For a real world (but clearly anectotal) example of this, lets compare Olympic marathon runners to sprinters. Many distance/marathon runners have very little muscle mass. Sprinters, on the other hand, tend to carry much more muscle mass (especially in their legs), while still maintaining extremely low body fat levels — in many cases their body fat to muscle ratios are much lower than distance runners. Sprinters typically train for short bursts of power and regularly utilize HIIT.
Interval Training also results in more thorough training. Because you are alternating between periods of solid-state and high-intensity exercise, Interval Training trains both slow and fast twitch fibers. This can improve your overall fitness, as well as overall performance and conditioning, explosive strength and power.
Interval Training and Heart Protection
A number of studies have suggested that High Intensity Interval Training may have protective or even recuperative benefits to the heart and cardiovascular system.
A 2007 joint study by the Norwegian University of Science and Technology, St. Olav’s Hospital, Trondheim, Norway; the University of Glascow and the Medical University of Ohio and published in the American Heart Association’s journal Circulation found that increasing cardio exercise intensity among patients recovering from postinfarction heart failure improved aerobic capacity, endothelial function and overall quality of life.
A January 2008 study by McMaster University and published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology found that low-volume sprint Interval Training (which is discussed below) had similar positive effects on the flexibility of arterial tissue as lower-intensity, long-duration cardio or running.
Decreased Boredom and Improved Exercise Motivation
Duration low- or-moderate intensity cardio can be boring and dull. Adding in Interval Training to your regular cardio routine can break up the monotony and keep things exciting. And the more you enjoy exercise, the more likely you are to continue with it.
When You Shouldn’t Do High Intensity Interval Training
While Interval Training is generally safe, there are a few circumstances when you should avoid it:
- If you are under a doctor’s order to only perform light or moderate exercise
- If you aren’t willing to do the critical warm-up period before engaging in the high intensity training
- If you have just started a cardio exercise routine and your conditioning base is still developing.
Beginners Guide to Interval Training
The best way to get started with Interval Training is to choose a cardiovascular exercise that you already regularly perform and incorporate bursts of higher-intensity exercise into them.
NOTE: Before you perform any Interval Training it’s important to give your body and muscles a proper warm-up, including stretching and at least 10 minutes of light cardio to raise your body temperature and prep your muscles for the higher intensity training that lies ahead. Do not skip this step.
There are a several ways to increase intensity — especially if you are performing Interval Training on cardio machines at the gym such as treadmills, stairsteppers, elliptical machines or recumbant/stationary bikes:
- One tactic is to increase the resistance of the machine for 1-2 minutes. On a treadmill, you can accomplish this by increasing the incline on the treadmill, which requires you to do more work. The trick here is to try to maintain your previous pace, even with the increase in incline.
- On elliptical machines, stair steppers or stationary bikes, you can also increase the resistance on the machine, which will cause you to work harder (and increase your heart rate) in order to maintain the same pace as before you made the increase in resistance.
- Another method of boosting intensity is to simply increase the speed on the machine, while using the same level of resistance as you employed during your low or moderate-intensity cardio. On a stationary bikes or elliptical machines, you simply do this by pedaling faster. On a treadmill or stair stepper, you increase the machine’s speed to cause you to run faster in order to keep up. So if you are normally jogging on a treadmill at 3 MPH, you increase that to 4 or 5 MPH (or whatever speed is required to take your percentage of MHR up to around 80 percent) for 60 seconds, and then return to your normal pace for 2-3 minutes to allow you to recover. You then increase the speed again, and then cycle into a recovery period and continue this approach for the duration of your training session.
If you are trying to incorporate Interval Training into activities that aren’t performed on gym machines — for instance walking, jogging, running or blading — you’ll generally have to increase intensity by increasing your speed. The same basic principles apply to these activities as with machine cardio.
Interval Training with Sprints
One of the most effective methods of interval training is to substitute sprints in for some of your duration or solid-state cardio.
Again, it’s important with Interval Training — especially with sprints — to give yourself sufficient warm-up time and to stretch. Before sprinting, do a fast walk or jog.
Sprints can be performed as part of a street running/jogging routine, on a treadmill at the gym, or preferably at a local track.
The approach here is simple, but highly effective: Run or walk at a moderate pace, and then sprint as hard as you can for 1 minute. Return to your moderate pace for 2-3 minutes and continue repeating the cycle.
If you are sprinting at a track, run as hard as you can for 100 yards (think of that “hundred yard dash” from grade school “field day”) and use the short end of the circle track to recover, and then run another 100 yard dash on the opposite straight track.
The goal here isn’t volume, but pure intensity. Initially, you shouldn’t expect to be able to do this more than a couple of times before your legs turn into rubber. Over time, you can work your way up to a dozen or more dashes.
The benefit to this approach is that you are not only burning a lot of calories during the dash, but you are also building muscle in your legs — something you typically do not get with distance running or cardio. This translates not only into additional functional power and speed, but also increased cardiovascular endurance and possibly more fat burned. Plus, it’s a fun change-up to pounding the pavement for 5K.
What About Using a Heart Monitor with Interval Training?
A heart monitor — while not required — can be a great addition to your Interval Training. One of the key principles of High Intensity Interval Training is to momentarily raise your heart rate above what you would normally experience with light or moderate cardio exercise. Generally, this will be around 80% of your maximum heart rate (MHR).
Using a heart rate monitor with your Interval Training can help you gauge whether you’re sufficiently increasing your intensity enough to get the full benefits of HIIT. Many exercise machines at the gym will have built in heart rate monitors that will allow you gauge your percentage of MHR — however, a heart rate monitor is one of the best ways to measure this in the absence of a built in heart rate monitor or during activities outside of the gym such as running, sprinting or roller blading.
Controversies Around High Intensity Interval Training
High Intensity Interval Training isn’t without its critics.
There are a number of exercise physiologists and fitness trainers who will point out that the body of published, peer-reviewed research on HIIT and body fat oxidation is actually limited to less than a handful of studies which were conducted with small groups of research subjects. Larger studies are necessary to validate some of the initial findings in Canadian studies around Interval Training.
Most of the controversy around High Intensity Interval Training has to do with the fat burning claims of HIIT devotees, and not with the research around increases in VO2 Max, improvements in cardiovascular health and conditioning or strength and muscle gains as a result of higher intensity cardio training.
Interval Training and EPOC: What About That Post-Training Metabolism Boost?
In particular, critics of Interval Training have taken aim at the post-workout calorie expenditure and whole body fat oxidation claims associated with High Intensity Interval Training. Current research indicates that Interval Training does increase something called “excess post exercise oxygen consumption” or EPOC — which is the measure of how much oxygen your body uses after exercise is completed.
Oxygen consumption is required for fat oxidation, so if EPOC increases as a result of HIIT, then this could account for some of the additional post-workout whole body fat oxidation observed in the University of Guelph study.
However, HIIT critics will point out that the effect of EPOC on post-workout calorie expenditure and fat burning is overstated. Recent research into EPOC shows that post-exercise oxygen consumption is elevated for a much shorter time than previously thought — perhaps as little as one hour. This is much shorter than the previous claims of EPOC persisting for up to 24 hours.
Practically speaking, this means that Interval Training may burn only a few dozen more calories after exercise than solid-state low-intensity or moderate-intensity training.
So if you normally burn 500 calories after an hour of moderate cardio, if you perform Interval Training you’ll have to ensure that your intensity and duration is still long enough to consume an equivalent amount of energy, since the post-workout energy consumption from HIIT isn’t going to make up a 100-200 calorie difference between the two forms of training.
This doesn’t mean that you won’t lose fat on an Interval Training routine, but it does mean that if you are counting on EPOC to give you that extra boost, the impact is so small as to be negligible.
That said, the actual physiological and bio-chemical mechanisms for the increase in post-workout whole body fat burning observed by the University of Guelp researchers, isn’t entirely understood even by researchers themselves. The study’s authors hypothesize that there may be more going on physiologically than just EPOC, including possible changes in the how the body preferences its source of fuel (fat versus stored carbohydrates in the form of glycogen) during Interval Training.
The Best Approach to Cardio: A Mixture of Interval Training and Solid-State Cardio
Science aside, at the end of the day, variety in your exercise routine is always critical. If you are planning on doing HIIT solely for the additional fat burning claims, you’re results may not be as dramatic as some of the headlines around Interval Training would have you think.
On the other hand, anecdotally there are plenty of people who have either switched entirely to High Intensity Interval Training, or incorporated it into their existing solid-state cardio routines and report making more overall progress in their fat-loss and fitness goals than when they were exclusively doing duration cardio at low or moderate intensity.
For most people the debates over the science of HIIT are primarily academic. Each person responds differently to exercise, and what works for one person won’t necessarily have the same effect on another. At the end of the day, the overall benefits of HIIT are substantial enough to try it out. If it works for you, keep it up. If it doesn’t, try something new.
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