When a friend asked me if I knew anything about Zone 2, I knew something was different. He wasn’t an endurance athlete and, at least I don’t think, trying to start a conversation for my benefit. It seemed like he wanted to share something he knew, something he recently learned. I found this both intriguing and perplexing. It’s not often I have someone from outside our clique approach me about training zones. I searched ‘Zone 2’ in Google Trends soon after our brief chat and, sure enough, search volume was through the roof. Was Zone 2 going mainstream? How did this happen and what does it mean?
Zone 2 is a moderate training intensity. At its most imprecise, an intensity that feels like you’re working, but allows you to hold a conversation comfortably (it’s called the talk test). At its most exacting, it’s a blood lactate concentration between 1.7 – 1.9 mmol/l (and requires a lactate analyzer- just back into heart rate and power numbers that correspond to the mmol/l values). Most of us use a middle way, or Zone 2 as a percentage of max heart rate or FTP. Just in case you’re new to endurance sport, FTP (functional threshold power) represents the most power you can hold for one hour.
Max Heart Rate 180 bpm X (Z2 Range 70% - 78%) = Z2 HR 126 bpm - 140 bpm
FTP 300 X (Z2 Range 56% - 76%) = Z2 Power 168W - 228W
The goal is to get your blood lactate concentration between 1.7 – 1.9 mmol/l. Because of the indirect measure, there are many interpretations and differing percentage allocations (I used the TrainingPeaks defaults above). But don’t sweat it, they’ll get you in the ballpark. If you want to be more exacting, go the lactate analyzer route.
It appears a special kind of magic (or transformation) takes place in the body when in Zone 2. First, you're in an aerobic state, which means there’s enough oxygen to fuel your working muscles. This is contrasted with an anaerobic state where there’s not enough, and your muscles are being starved. Important transformations happen in both conditions, but they are not the same, and it’s only recently that Zone 2 transformations are being fully understood and harnessed. The ‘magic’ that takes place is the increased mitochondrial density. Mitochondria are the ‘powerhouses’ of the cells and can’t function in an anaerobic environment, but flourish in specific aerobic environments. It’s here mitochondrial biogenesis takes place, the process that creates new mitochondria in your cells. These ‘powerhouses’ multiply and it looks like it’s Zone 2 that nurtures this development. There are many downstream benefits from here, such a greater utilization of fat and lactate as an energy source, greater lactate clearance and more efficient ATP production. Zone 2 tills the soil and mitochondria bloom.
Tadej Pogačar’s coach revealed the amount of time he spends in Zone 2: 80%. For those unaware, Tadej is the new Eddy Merckx, has won the Tour De France and Giro D’italia, monuments, and classics alike. He is being called (fairly in my opinion) the greatest of a generation – and he spends the majority of his training in Zone 2. To be clear, all other zones have an important place in workouts, and high-intensity interval training (hiit) remains especially critical to success, but the Zone 2 revolution has rearranged our priorities. It should also be noted that Tadej’s power in Zone 2 would be closer to my threshold (so he’s not actually going that slow), but all the same, he’s deliberately training a low-intensity zone to build up his mitochondrial function.
The Zone 2 insights (among others) have ushered in new training models for endurance athletes, new to me anyway. It seems the Norwegians have been playing with these themes for decades. It’s called ‘polarized’ training or ‘80/20’ and I’ve learned a lot from the work of Dr. Stephen Seiler of late. I’m not alone here; he’s now woven into the coaching certification process at USA Cycling. The long and short of it is that your calendar now has a more Zone 2 volume on it. As you approach A and B events, you’ll reduce this volume and layer in high intensity (as usual), but this approach emphasizes more time in lower intensity zones, strategic time in higher intensity zones, with middle intensity zones reduced (hence polarized). Dr. Seiler promotes a three zone model, each zone corresponding to a lactate turn-point. I won’t wade into the details, this is only to say Zone 2 as I’m defining it here is prior to the first lactate turn-point.
We endurance athletes are often carrying bags we don’t realize we are carrying. By this I mean we have in-built assumptions about what is required to get faster and many are false. I am delighted that the myth of ‘no pain, no gain’ is being dispatched. I’ve lugged this bag around for too long. On reflection, many of my most cherished memories as an endurance athlete are not winning races (there’s some of that) but of long slow rides with teammates and friends. The idea that these rides are just as critical to success as the grueling interval work portends a happier, healthier social environment less prone to burn-out and overtraining. It makes for a better scene.
Zone 2 has reached a more general audience for a simple reason, it promises a lot for doing a little. Anything that offers more benefit than cost is contagious, is shared and promoted, and functions with a memetic logic. Funny enough, the reason many endurance athletes are suspicious of Zone 2 is the very reason it was able to penetrate the mainstream; improvement doesn’t require herculean intensity. No pain with gain, Zone 2 promises. Personally I am thrilled with the popularization of Zone 2. At this point, we need as many barriers to exercise to fall as possible, even if popular notions of Zone 2 are misconstrued.
There’s no free lunch in the end because you need lots of time (volume) in Zone 2 to confer the benefits. I don’t mind because long slow rides with friends are pure joy, and knowing that they are now part of a serious training program makes them all the sweeter. For our general audience, I am thrilled that Zone 2 has punched into the zeitgeist. I read it as a sign that we’re getting ready to incorporate exercise back in our lives. We’re still looking for shortcuts, sure, but even looking at this point is progress. Zone 2 training for us endurance athletes shouldn’t be confused with a shortcut, you still the volume. But for those of you that think intensity is the only way to get faster, I’d recommend you go on a long slow ride and discuss it with friends.
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