Interval training has become the hottest fad, with people decrying steady-state cardio, and promoting high-intensity interval training (HIIT) as if it were the only way to train. You’ll hear grandma’s discussing their Tabata Protocol numbers at bus stops, hear snickers as people walk by people jogging along slowly, and in general run into the belief that if you’re not HIITing it, you might as well not bother. What is HIIT? Is it really the ultimate way to train for cardio? What are its benefits, and what are its potential problems?

First, let’s define some terms so that we’re all on the same page. Interval training is any kind of training that alternates hard bits with easy bits. If you think about it, even lifting weights can be considered weight training, as you’re alternating resistance and rest. However, we’re going to narrow in the focus of this blog post to consider a specific kind of interval training, which is High Intensity Interval Training. However, even in HIIT there are variables, such that you can have different intensities, durations of work and rest, number of reps, number of sets, and rest intervals between sets. As you can see, there are scores of different ways to perform HIIT, but we’ll get to that in a bit.

HIIT tends to be any form of cardio work done in short bursts (typically from 15-2o seconds to maybe a few minutes), and the intensity that you measure is usually your lactate threshold, since it’s that overriding burn that will stop you from going on, rather than any other limitations. Heart rates aren’t generally useful here, because it takes your heart a couple of minutes to react to exercise, and since HIIT is so short, the workout is generally over by the time your heart rate begins to reflect your true state of exercise. The goal really is to go all out: you want to red line it as much as you can during your rep, so that you have nothing left when the set is over.

Now, let’s talk about something that most people never address, and which is crucial to understanding the benefits of HIIT. Take a car: it has a top speed, and a fuel tank. It’s ability to travel is dependent on both; it doesn’t matter if it can go 200 mph if it’s tank is only 1/4 gallon. Similarly, people have power (ability to generate force), and capacity (the ability to sustain it). HIIT affects these abilities, but often not in the way people think–or understand.

Why do HIIT? What’s the benefit? ‘To get tougher’ or ‘To get fitter’ are too vague to be of any real use. Let’s take a look at some specifics, and see how HIIT can benefit your system.

Ability to perform anaerobically: If you operate above a certain threshold, your body will start to rely on anaerobic processes, and will also begin to generate waste that will cause your muscles to fatigue. This generally occurs if you are working out at about 60-90 seconds, at which point your whole body is burning, you can longer breath, and have to slow down. Think about all-out sprints, and how long you can sustain them. Training to improve your anaerobic ability will usually look like this: 30-60 second all out effort, with several minutes break right after, repeated some 8-10 times. You generate a massive amount of waste, but raise your ability to generate immediate power and process that waste that your body generates.

Your VO2 Max. Now, this is a slightly technical idea, but bear with me. Your VO2 Max is the maximum amount of oxygen that your body can use. This is determined by your heart’s ability to pump blood, and your muscle’s ability to extract and use the oxygen in your blood. HIIT can help improve your heart’s ability to transport oxygen to your muscles, since it targets heart function first. Studies show that, in the short term, interval training can greatly improve your VO2 Max, much more than steady state cardio training. This is where a lot of the hype about interval training comes from–the fact that it can improve your heart function much faster than steady state cardio.


So why not do HIIT all the time? Because of certain key limitations. Studies have shown that the benefits accrued by interval training tend to stop after 3 weeks in most athletes, though beginners can still see benefits 8 weeks in. Beyond that point, your anaerobic and VO2 Max abilities tend to not improve much. Which means that if you keep on killing yourself (because HIIT is brutally, terribly hard to do) beyond those first two months, you’re generally wasting your time.

The other drawback is that HIIT can improve your top speed, but not necessarily the size of your gas tank. You’re basically training your ability to explode into action, to sprint, to generate immediate power. However, nobody can perform anaerobically for long. While you may improve your ability to process waste and last longer, you still need a good cardio engine to keep going. Which is why nobody should just do HIIT–you’ll be able to sprint incredibly for a few minutes, and then die as your system is overloaded with lactate.

Question: Is the INSANITY workout a HIIT workout? The answer? No. HIIT by definition is red lining. If you’re HIITing it, you can only go for a few minutes. INSANITY workouts can last up thirty or forty minutes (not including warm up and stretches). So what is the INSANITY workout considered? Is it not interval training? Find out tomorrow in our next blog post 😉

Photo credit: Matt Eastman