2012-03-14

HIIT Clarity

In a recent post called "Pop Fitness," I discussed the modern trend toward HIIT-dominant training in popular exercise regimens. One might almost be left with the impression that I advise against HIIT (high intensity interval training). If one did have that impression, though, one would be mistaken.

In short, HIIT is a great addition to any exercise regimen, but one should be careful viewing it as some sort of fitness panacea, and one certainly shouldn't use HIIT as the predominant cardiovascular exercise activity. In this post, I'd like to describe why I'm right about that.

Problems With the Clinical Studies Reinforcing the Supremacy of HIIT
At a cursory glance, all (or most) of the clinical evidence seems to suggest that HIIT is healthier than what we might call "traditional cardio training." To understand why this is not necessarily the case, I'd like to make a few points about these studies and their results.

1. Study Cohorts
In most of these studies, sedentary people are introduced to a new diet and exercise regimen. One group engages in traditional cardiovascular training, while the other follows a HIIT-dominant regimen. Invariably, the studies reveal that the HIIT cohort out-performs the control group.

What you do not see is a comparison of, say, marathon runners separated into classic marathon-training cohorts and HIIT-only cohorts.

While it certainly appears to be true that exercise newcomers can realize major gains from a cardio regimen that emphasizes HIIT, it is less clear to me whether experienced, life-long health nuts are better served with one over the other. As far as I can tell, no study has net tackled that particular question.

2. Short Follow-Up Periods
Another problem with these studies is that they typically range from about three to twelve months; usually, about six months. Six months is more than enough time for an otherwise-healthy, sedentary person to get into great shape. That said, a person with five years' exercise and fitness experience has already been training for ten times longer than a six-month study period.

In short, six  months is a drop in the bucket. I consider six months to be a short-run time horizon. While HIIT-dominant training has been repeatedly proven to yield excellent results in six to twelve months, it is less clear what are the comparative impacts of, say, a decade of HIIT training versus a decade of traditional endurance training.

One important question would be: is it even possible to engage in HIIT training for that long without experiencing over-training, injury, and eventually defaulting to more traditional forms of cardiovascular exercise?

3. Is An Exercise Program's Efficacy Simply A Question of Total Calories Burned?
Too often, the benchmark for concluding HIIT's superiority is the fact that the study participants burned more calories than their counterparts. Is that really all that matters?

As I alluded to in Point #2 above, doing HIIT absolutely every time you do cardio will almost surely fatigue your muscles and present a risk of injury. Recovery, including long periods of less-strenuous activity to help neutralize intramuscular acidity, is an absolutely vital aspect of using HIIT training effectively. A few weeks of HIIT plus a few weeks of injury-recovery is obviously inferior to the same number of weeks of consistent, injury-free exercise.

Moreover, muscle tissue basically comes in two varieties: that which serves strength/speed, and that which serves endurance. The strength/speed tissue is highly efficient in an anaerobic context, but it is the endurance tissue that burns fat cells most efficiently. (See my post on fitness trade-offs for more information.) A HIIT-dominant plan will get you burning calories and building muscle - and these two things are great! But only endurance training will maximize your body's ability to burn fat.

Finally, while HIIT is an effective way to burn calories and fat, it is probably not the best way to manage other aspects of physical fitness, such as flexibility, balance, agility, muscle coordination, and so forth. Which brings me to my next point...

Pop Fitness "Big Picture" Conclusions
If you spend all your time reading Women's Health or Men's Health or other such magazines, you begin to construct a view of the world that emphasizes diet to achieve weight loss and resistance training to achieve physical fitness. For your the remaining cardio-needs, you are advised to engage in HIIT. What this paradigm creates at its ultimate conclusion is much of what you see at the average fitness club: Lots of people with good body composition who haven't played a real competitive sport at a competitive level for years.

I'm not saying you have to, either.

What I am saying is that the question starts to become meta: What is fitness, anyway? If the average gym denizen is the picture of fitness, then where does that leave Lance Armstrong? Is he "fit" despite having smaller muscles and bench-pressing less weight than your Gold's Gym personal trainer? Is a world-class marathon runner "fit?"

Here's the point: I assert that competitive endurance athletes are more fit than the average CrossFit participant. This is not because I think endurance training is superior in every way, but rather it seems obvious to me that anyone whose body can perform any activity at a level that only a handful of other human beings even understand, it stands to reason that that person's body is in better physical shape than the average person who gets 3-6 days of weight training done per week.

And just to be perfectly clear, I think the same is true of world-class weight lifters, even though they could never run a 5K as quickly as I can. They are fitter than I am because their bodies can meet demands that can only be met by a small minority of people.

So, to sum up: Is fitness simply a question of eating right, lifting some weights, and doing some HIIT, or is there more to it than that?

Answer: There's More To It Than That
It is patently absurd to boil fitness down into three simple activities that will turn anyone into someone worthy of being on the cover of a magazine. You can't just eat walnuts and do CrossFit and turn yourself into the picture of perfect health.

That's not to say that walnuts and CrossFit are bad for you. They are obviously very good for you. Just like HIIT. But these things are not a panacea.

True physical fitness involves a wide array of training options. A good running program, for example, will include long runs, IT, HIIT, weight training, plyometrics, and recovery workouts.

See, fitness is the whole picture. HIIT is great, and highly effective, but you can't do it every day. Doing it once or twice a week, though, is a whole other story. In the right doses, HIIT can take your fitness to the next level. Too much is at best a sacrifice and at worst a risk of injury.

So don't just assume that HIIT is the only thing you need, just because it got some positive press. Use your head! Being fit means more than just exercise X or exercise Y. Being fit means pushing your body to the limits and reaping the rewards associated with a higher level of athletic performance.