By Steve Edwards (Beachbody)

There are a lot of misunderstandings about the best way to reshape your body. This is because there are a lot of trainers out there who espouse different fitness philosophies. In general, the various regimens touted all have some merit. In this article, we’ll take a very simple look at various training strategies, bust a myth or two, and explain why interval training is the most efficient way to change your fitness level.

We’re just about to launch a program called Insanity™, featuring Shaun T, which is a high-intensity conditioning program that’s based on something we call MAX Interval Training. While it’s the most intense workout program we’ve produced, it’s not the first to use interval training to create fast results. In fact, every Beachbody® program uses some type of interval training.

What is interval training?

In short, you are interval training any time your workout includes a set wherein you perform at your maximum level, which is then followed by a lower-intensity set, which is then repeated to achieve a cumulative effect. An interval can be a set of curls, a dance move, or anything that tires you out over its given interval of time. The intervals can be short and hard, or long and easy, but they’re all intervals, just so long as there is some cumulative effect (you get more tired as you go). All interval workouts aren’t the same, though; the duration and intensity of the intervals are what define the workout.

Conversely, aerobic training is when you maintain a steady output at a low intensity level over the course of the workout. We do offer some workouts that do this, but they are generally either for recovery or for the second daily workout of a doubles program. This type of workout helps your aerobic efficiency but does very little for changing your body.

The myth of the fat-burning zone

It’s impossible to approach this topic without debunking the term “fat-burning zone.” You often hear uninformed trainers recommend that their clients reduce the intensity of their workouts so that their bodies will burn more fat. In reality, all these trainers are doing is lowering the overall effectiveness of their clients’ programs.

Here’s a quick explanation of the fat-burning zone. At an aerobic pace (see above), your body utilizes stored body fat as fuel to save its preferred fuel (stored blood glycogen) for more pressing matters. It sounds great because you’re burning body fat. And while this is true, you’re burning it at a very slow rate.

During higher-intensity work, your body turns to a limited supply of blood glycogen (often called blood sugar) for energy. While your body’s burning glycogen during this more intense period, and not fat, it’s breaking down more body tissue. Breakdown is a bad word for a good thing, because your body produces more hormones and increases its metabolism to repair this breakdown. As the tissue repairs itself, it builds more muscle so that next time you do a stressful workout it won’t be so taxing. This process of adapting to intense exercise is where your body makes rapid change.

Continually building on this process is called progressive overload. By continually adapting to stress and then adding more (either with weight or speed or programs like Insanity), you increase your body’s fitness so that it’s actually burning body fat for fuel as you rest. Interval workouts should be a key component in every phase of your training.

Techie science made simple

Asked what separates serious and recreational athletes, author and fitness trainer Steve Ilg replied, “Intervals.” But since “intervals” is an umbrella term for training that targets many different energy systems, it’s quite a cryptic statement requiring further explanation. It’s also pretty accurate. Recreational athletes like to train within their comfort zones. Interval training, regardless of the targeted intensity level, always forces you out of it. And you must be willing to leave your comfort zone if you want to see significant changes in your fitness level.

Interval levels can change dramatically. For example, HIIT (high-intensity interval training) workouts are very short, sometimes only lasting seconds, and completely anaerobic. Marathon runners will often run for 1- or 2-mile intervals, which can take many minutes and are obviously somewhat aerobic. The reason for the varying intensity of intervals is to train different energy systems in the body. These are defined by terms you may have heard of, AT (anaerobic threshold), VO2/max, etc. For our purposes, you don’t need to know these terms. Here’s the 101 version.

LSD. Not the hippie drug from the 60s, but rather long slow distance. This is not an interval; it’s a term you’re likely to hear especially if you know or are a runner or cyclist. Its purpose is for base-level aerobic conditioning. As I said above, it’s not very applicable for making significant body changes, unless you do it for a very long time. Yet many trainers still recommend it. I think this is primarily because their clients won’t complain about doing 30 minutes of easy exercise.

Sports-specific intervals. These can be anything, like the 2-mile example above. Interval training exists for all athletic endeavors. Since it’s targeted for sports performance, we won’t discuss it. You’ll learn plenty about it when you join a local group to train for a triathlon or something else.

Weight training intervals. All weight training could be considered interval training, but traditionally, you rest so long between sets that you don’t get a cumulative effect. All Beachbody weight training is done interval-style, which we call circuit training. During these workouts, you move from body part to body part without much rest between sets so that the workouts don’t just target muscle building but also improve your cardiovascular fitness. Power 90® and Slim in 6® are good examples of this kind of training.

What defines these circuits is your targeted number of repetitions. A low target using more weight will create muscular hypertrophy, or growth. A higher number limits muscle growth (you get some muscle growth) and gives you more cardiovascular improvement.

Cardio intervals. These are what most of you probably define as interval training. First, we must define the difference between cardio and aerobic. Cardio means heart, while aerobic means oxygen. Aerobic training is most easily defined by the word “easy.” It’s really defined by training below your anaerobic threshold, but we’re dispensing with science talk. Cardio, however, is all training that affects the heart. So it can include aerobic training but also all the high-intensity training associated with intervals.

High-intensity cardio intervals are performed in something we call heart rate training zones. Cardio intervals target these heart rate training zones for various periods of time. When you design your own interval workouts, you must do this yourself. When you have a trainer, he or she does it for you. This is why we at Beachbody always have test groups to make sure our workouts train you in your proper zone. That way, all you need to do is follow along.

MAX Intervals ‘n’ stuff

In general, the longer the interval, the easier the workout. Some interval sessions have long and moderate intervals with short aerobic breaks. Others have short, difficult intervals with long aerobic breaks. What makes Insanity’s MAX Interval Training unique is that it combines long, hard intervals with short breaks.

The MAX Interval system is based on HIIT, though it’s not HIIT. HIIT includes very short maximal intervals, followed by short breaks. It’s very intense and also effective. Its downside is that it’s so intense that your body can’t do it for very long. You can generally only see good progress for 2 to 3 weeks at a time using HIIT workouts until you need to transition to a different type of training.

Conversely, a more traditional approach to interval training, like Turbo Jam®, that relies on various intensities of intervals (mainly moderate) can be done for very long periods of time before you need to change workouts. Your fitness improvements won’t be as drastic, but they’ll be steady.

With MAX Intervals, we lowered the intensity of HIIT just enough to keep the high-intensity format but to also increase the time during which you can make rapid improvements before needing a break. The result is a high-intensity interval training system that keeps yielding results for a long time before you need a transition.

How to incorporate intervals into your workout program

Like every other aspect of fitness, your starting point should be based on your current physical condition. If you aren’t very fit, you’ll want to start with a very basic interval program, which will still feel hard. Workouts like Slim in 6 Start It Up! or Power 90 Sweat Cardio 1–2 are perfect introductory interval sessions. If you’re in doubt, start slow. It’s easier to increase your workout’s intensity than to go backward.

You never want to begin with HIIT or MAX Intervals, unless you’ve got a solid fitness base. This style of workout is so intense that you won’t even be able to finish each workout, negating the whole interval aspect. And even if you do finish, training this hard out of the gate increases the risk of injury.

Intervals are the most effective way to see quick results from a workout program. If you’re not doing them, add them right away. If you’re already doing intervals, perhaps it’s time to step up to the next level.