We may have miscalculated folks. It is ever more apparent that HIIT, work in excess of 75% VO2 Max, high volume training protocols (think many thousands of reps/group functional fitness) and general glycolytic work comes with a host of unintended, unwanted consequences for many of its adherents. Moderate intensity exercise may be the sweet spot.

Much of the metabolic magic, for what I call us “normies”, appears to reside in the “easy” stuff. What I call Zone 2 work with my clients.

“Modern humans are physiologically better adapted to exercise intensities similar to ones their hominid ancestors evolved with rather than those supported by modern societies.These would have included daily bouts of prolonged, low-intensity, aerobic-based activities, which are primarily fueled by the body’s long-term energy source: fat.”
– Phil Maffetone

The problem with HIIT, high intensity cardio and group functional fitness.

1. Substrate Utilization

Generally speaking the more intense the effort becomes the more your body needs to burn sugar to fuel the metabolic engine and the less it is able to utilize fat as fuel. Below is a chart from Phil Maffetone’s site showing a progression of fuel utilization from less intense to more intense effort.

These figures are for a seasoned athlete capable of running a 5:25 mile. For the rest of us mere mortals you can bet the numbers are less optimistic. Which is to say you should slide everything backward in your mind and realize that it will take an even lower heart rate for you to burn the same amount of fat that the above individual burns at any given output.

The more volume of high intensity sessions you accrue and the less low end aerobic work you do, the more you will be more predisposed to burning sugar at lower intensities/BPM. This is precisely the effect you don’t want your exercise to have on your metabolism.

2. The Vicious Cycle

Most folks are obligate sugar burners by virtue of their diet and lifestyle choices. They likely may never realize 70% fat utilization in their current condition. This is to say they are not metabolically healthy or flexible.

Although we don’t typically refer to training protocols as “lifestyle”, it is a lifestyle choice. The same individuals that are not lean and/or are not metabolically healthy, also choose to fill their training time with high intensity aerobic or glycolytic sessions. In this case the majority of their “workouts” demand sugar/carbs while the brain turns a blind eye to fat (that pesky ring around the belly). And because of that intensity, guess what food substances they are left craving to fuel those efforts once they get home? More sugar and carbs of course.

Ever look around a functional fitness gym and see a room of faithful devotees, flogging themselves with intense exercise on a daily basis, that carry that same pesky ring around the belly? They can’t seem to lean out…I’ve seen it for years. Although we tend to focus on the beautiful people (chiseled like Spartans), they are largely outnumbered by the former, by the general population.

This begs a question around alignment. Do your goals, food choices, lifestyle and training align well?

3. The Price of Admission

Those high intensity sessions come with a host of consequences that are wildly unpopular to mention in online pop fitness ramblings, mags, tv etc. Free radicals and accelerated aging, hormone dysregulation, accelerated degradation of joints and connective tissue, and the previously mentioned vicious cycle issue with all of the accompanying metabolic damage that comes with it.

Consider the average devotees activity profile, it lacks a transition, a buffering effect. It looks like a richter scale for the most part. Zero to one hundred in no time flat. People are almost totally sedentary 90% of the time, then they walk into a gym and redline themselves for their exercise session. Then back to sitting. Almost nothing in between. You shouldn’t even operate your car like that. It’s a problem.

I’m not going to try and make some airtight scientific case here, you can go on PubMed, NCBI and other sites and try and make some sense of all this yourself. Suffice it to say I’ve watched it play out many times over the last 12 years of my career. I’ve personally paid a price for my early years of not being “in the know” around some of this and I’m certain many former clients and zealots have as well. You don’t need a double-blind, randomized, controlled study to verify something you have witnessed first hand – many, many times.

A lot of people are there for the “hit”. This is exercise as a drug. Others are there presumably because they think metabolically intense efforts are the best way to get what they want, namely to look good naked. Others for communion or perhaps for the suffering. Which is understandable. Whatever the case, the collective is logging a lot of volume of the wrong sort, a lot of intensity and paying a price they don’t fully understand while doing it. Unknowingly sabotaging goals and results along the way is just a slap in the face as a bonus.

Once that price has been sufficiently exacted, whether it is fully conscious or not, people realize that the path they’re on is not sustainable. There is no alignment between who they are, how they live, what they want and their training protocol. Then they jump ship. They are often at a loss for what to do next (insert latest “intense” exercise fad here or maybe a total bail out on any decent strength work moving forward). Often they are broken in one or more ways from too much intensity, too often, prescribed way too soon. They may be feeling bummed about their “failures” or their inability to continue with an exercise regimen they thought was on point.

So, is there a better way for the masses? The answer is a resounding “yes!” I call it “Zone 2” work. It doesn’t matter what you call it though, as long as you know what it is, why you should be devoting your time and energy to it and how to effectively execute it.

Remember we are only talking about metabolic work now, not strength work. Strength work is the most essential piece of a training program and should run concurrently with any metabolic efforts. As should a robust mobility and stretching program.

What is Zone 2? 

Let’s call it cyclical work somewhere between 60-70% (max HRM). This of course varies from individual to individual. Often drastically. It’s important to be honest in every regard when assessing where your own Zone 2 likely is. Basically, the more deconditioned, in poor health or older you are the lower your BPM will need to be (at least initially) to approximate this zone.  Metabolically healthy individuals and people that are more aerobically conditioned will be able to hit this sweet spot of training at higher BPMs.

Why should this constitute a majority or appropriately large percentage of my training time?

1. When we activate the Type 1 muscle fibers using Zone 2 work we stimulate mitochondrial growth and function. Many of the sharpest minds in medicine, physiology and health are well aware that the mitochondria and their function appear to be the foundation of our health, longevity and athletic performance. Conversely their lack of function and vigor appear to be deeply tied to the most serious pathologies of our time. Zone 2 training currently seems to be the method for fostering our mitochondria. Certainly in Type 1 fibers anyway.

2. Through Zone 2 training you maximize your body’s ability to use fat as fuel. Not only during the session but also while at rest. This is a cornerstone of metabolic health.

If you fancy improving your performance in any kind of endurance sport, you also train your body to spare all that glucose until such time as you really need it. In this way, you hedge against the “bonk”. You are making yourself less prone to bonking relative to those that did not dedicate sufficient time to Zone 2 training.

3. You improve your body’s ability to clear lactate. Also a kind of holy grail when we talk about athletic performance. Both in endurance work but also over the domain of shorter, more intense glycolytic efforts.

4. Doing Zone 2 work can be regarded as the definition of building a strong “aerobic base.”

5. It is the most appropriate work for the greatest number of people who exercise. Here’s the cold, hard truth—most of the population is broken. For example, the CDC reports that 88 million adults in the US have pre-diabetes! If we lump in all the Americans who demonstrate the hallmarks of metabolic syndrome, the numbers get even worse.

And then there’s the mundane. People are under slept and under rested, overworked, over stressed, have poor mental health and are generally in a bad place physically. They’re bound up and broken down. They’re on pills, Rx’d or over the counter, using alcohol in copious amounts and have all kinds of structural problems and injuries. A growing number have no basis for, and no resiliency to, the HIIT and Metcons they are subjecting themselves to day in and day out.

The beauty of Zone 2 is that it takes very little from you other than time. It doesn’t beat you up. And it does not require or make you crave large amounts of sugar and carbs in the way that high intensity sessions do.

Zone 2 optimizes your metabolism to burn to fat, provides the foundation of your aerobic base and improves your lactate clearance. Additionally it can be a better choice for the majority of sessions for folks who need to get more parasympathetic (read damn near everyone).

“ A training session should give you more than it takes out of you.”
– Pavel Tatsouline

How do I effectively train this energy system?

Currently I use Maffetone’s 180 Formula in my own training and for my clients as well. We do testing at the precise number arrived at by the formula and prescribe cyclical work up to that number but often lower. You can calculate it yourself by subtracting your age from 180 and then making the fine adjustments contained in the links to maffetone’s articles at the end of this post. Once you have what I would call your top end Rx BPM you need a decent heart rate monitor. A chest strap or the next gen arm bands are probably the best choice. Find yourself a cyclical machine (stationary bike, rower, treadmill etc.) and log some time between 10-15 BPM lower than the 180 Formula and up to that number.

It’s important to understand there are numerous “formulas” for isolating “Zone 2.” They are all imperfect. I currently like Maffetone’s the best for the general population. If you compare it to the standard 220-Age x .6-.7 method, you’ll see it may shake out closer to 70-75%. Hence my recommendation for doing work down to 15 BPM lower and topping out/testing at the 180 Rx. 

Over time you will get a good subjective feel for just where your Zone 2 is and the level of exertion that it entails (surprisingly low for many fitness enthusiasts). Then, when you don’t have a heart rate monitor, you should be able to reproduce a very similar effort in less perfect conditions such as a casual bike ride, walk, hike etc. Subjective measures of this effort are commonly associated with being able to pass the “talk test.” When doing Zone 2 work you should be able to hold a conversation. The pace should be continuous and stable with good blood flow and breathing. 

As far as the minimum effective dose and frequency, the jury is still out. Currently, I work with two times per week for at least 30 minutes. A better recommendation is likely 2-5 hrs/week. It varies by individual, but you have to start somewhere. Much of the impetus behind that particular minimum simply has to do with the scarcity of time. Busy people in 2020 have none. So again, use this as a starting point to build familiarity and consistency. You can always devote more time from there.

Zone 1

It’s worth mentioning Zone 1. If we view this as a pyramid, Zone 1 is the foundation. Easy movement, like walking. Some folks, very sedentary types, will have no business doing Zone 2 work initially. While they may represent a small percentage of this article’s readership, they represent a significant portion of Americans. Those folks need to begin with a focus on Zone 1. 

If Zone 2 allows you to have some level of intensity while still being glycogen sparing, Zone 1 may be the ultimate in terms of requiring virtually no sugar. A healthy individual on a ketogenic or very low carb diet should be able to do Zone 1 all day with no real cravings or necessity for dense carb and sugar sources.  

You wanna do it anyway? Go for it. But first..

  1. Understand the costs.
  2. Get your house in order and fix your food and lifestyle so that you can be more resilient to the aforementioned negatives. 
  3. Earn it! It takes time and smart, progressive work to get there. 
  4. Instead of impaling yourself on it every training session, use it sparingly (min dose max response) and use it intelligently (smart program design).

If you’re an athlete that regularly competes for points and medals, that’s a different story. It’s not to say that there’s nothing of value in this post for you but of course athlete’s do what they need to do to win. And the smart ones knowingly accept the cost of that choice.

In closing I’ll say that of course there are going to be positive adaptations that result from intense metabolic training. And for competitive athletes (individuals who regularly compete at the amateur/pro level) it’s essential for peak performance. However, it is hardly the panacea it has been made out to be when it comes to the general population. In fact, it’s often wholly inappropriate when you consider who they are, how they live and what they really want. When you combine that with the physical and metabolic costs of running an “intense” training protocol ad nauseum for years on end, you get sub optimal results.

Perhaps it’s time to rethink the template for the great majority. To create something that is more in alignment with the needs of the many.

For further reading enjoyment:

MAF 180: Personalizing Exercise Heart Rate

An update to the MAF 180

Zone 2 Training For Endurance Athletes

For a deep conversational dive on all this, check out Dr. Inigo San Milan‘s conversation with Peter Attia on “The Drive” podcast.