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'Zone In' for Cardio that Works

Updated: Mar 16, 2023

Whenever I start talking to clients about 'cardio,' responses typically fall into one of three categories:

1) Cardio is life (and they do too much, and usually too high-intensity)

2) Cardio sucks (and they do too little)

3) I do cardio because I sort of think I have to (but they aren't quite sure if they're doing enough, too much, or even what kind of cardio is 'worth it' to do)

With the Type 1 clients (aka the "cardio bunnies," aka the HIIT addicts, aka the Spinners), I find myself trying to explain the importance of moderate-intensity baseline cardio and not exceeding the anaerobic threshold (or worse, get injured from all the jumping around). With the Type 2 clients (aka the "heavy lifters," aka the ones that skip all cardio for fear of losing their gainz), I find myself trying to explain the importance of regular cardiovascular exercise for heart health, and why some level of cardio is necessary for body recomposition.

And with the Type 3 clients (aka "everyone else," aka the people who are a little confused about the role of cardio in a regular exercise program and how much is actually necessary), I find myself trying to advise around everything from F45 to marathon running to hot Pilates to answer the question, "does this count as cardio?"

Luckily, there's a singular answer for all three types, and it's backed by science: ZONE 2.

"Zone 2" exercise has gotten a lot of press lately as the cardio format du jour of experts like Peter Attia, Fergus Crawley, and Dorien van Aggel-Leijssen. The idea is that at a specific "zone" of intensity (measured most accurately by continuous exhalation testing like VO2Max), your mitochondrial activity is stimulated the most - meaning you burn the most fat (versus carbs) for fuel.

Sounds great, right?

Problem is, most recreational athletes are jumping straight to higher zones - think 3, 4, and 5 - which burn primarily carbs for fuel, missing out on the mitochondrial and fat-burning benefits of zone 2 entirely.

The great - and confusing, to seasoned exercisers - thing about Zone 2 cardio activity is that it isn't painful, and it doesn't take any great efforts to achieve. In fact, most professional (think Olympian) runners spend 80% of their training time in Zone 2 - meaning that, contrary to popular belief, what separates the pros from the amateurs is that they spend more time going slow and easy (relative to their training levels, of course).

So how does this apply to us non-Olympians out here just tryna get lean and fit?

It means that if one of your top fitness goals is to lose body fat, Zone 2 cardio is the most effective form of cardio to help you do that. Take note:

If you're really committed to knowing your exact, personalised Zone 2 threshold (because, yes, it is highly individualised depending on a variety of factors), your best bet is to schedule a VO2Max calorimeter test at our LIFT Lab and find out the exact intensity of exercise at which your body starts burning fat for fuel (as well as the exact point at which it starts burning carbs, so that you can stay beneath that intensity if fat burn is your goal).

If you want an easier approximation of Zone 2 effort, you can use your heart rate (Apple Watches and other trackers automatically record this data when you log your workouts - check the "heart rate" section of your Activity app afterwards to see your zones!). A "Zone 2" heart rate is generally 70-80% of your maximum heart rate, which you can approximate here (this calculator calls it the "moderate aerobic zone").

If you want something even easier than that, consider the "talk test" - if you were on a phone call while performing Zone 2 exercise, the person on the other end of the line should be able to tell you're exercising, but you wouldn't be so out of breath you can't talk comfortably for the full hour.

...which, yeah, brings me to my next point.

Ideally, you'll need to perform Zone 2 cardio for 45-60 minutes per bout, for a total of 150-180 minutes per week. The minimum effective dose is 45 minutes per bout, so this isn't one of those "break it up throughout the day" things - to get your mitochondria really rockin', you need to hit the 45-60 minute duration, and maintain Zone 2 intensity throughout (no fair dropping down to Zone 1 to "recover" or pushing hard to Zones 3 and 4 to "get that burn" - both of these are not-so-lovingly referred to as "garbage zones" when it comes to fat oxidation and maximum fat burn because they don't work).

A final note on Zone 2, in case I haven't convinced you already - Zone 2 cardio can be any form of cardio, as long as it's steady & sustainable for 45-60 minutes for you personally. You can swim, bike, jog, hike, row, or ruck your way into Zone 2 - just make sure you stay there.

Coming back to my three types of clients - as you can tell, there is a "best practice" when it comes to cardio, and it's a bit of a blend of all three approaches. You need some (not none), you need it to be moderate intensity (not too high, not too low), and you need to do it 150-180 minutes per week (an exact amount). Now take your marching orders and get Zone 2-ing!

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