체력 기르는 방법 등으로 찾아보면 요즘 많이 검색되는 것이 두 가지가 있다. 하나는 잘 알려진 최대 심박수를 왔다 갔다 하는 '인터벌 훈련'이고 상대적으로 덜 알려진 '존 2 훈련' (Zone 2 Training)이다. 존 2 훈련은 '장시간 저강도 유산소 운동'을 의미하며 저강도 존 2 훈련:고강도 인터벌을 80% : 20% 비율로 섞어서 해주는 것이 좋다고 한다. 많은 사람들이 연구해 보니 전반적인 체력 향상에 있어서 일종의 sweet spot을 찾아보니 80:20의 파레토 법칙을 따른다는 것이다.
여기서 존(Zone)이라는 것은 분당 심장 박동 수(심박수)의 범위 또는 영역을 말하며, 보통 자신의 최대 심박수의
. 50~60%를 Zone 1 (웜업, 일상적 움직임)
. 60~70%를 Zone 2 (Fat-burning=지방 연소)
. 70~80%를 Zone 3 (Cardio=유산소 영역)
. 80~90%를 Zone 4 (고강도 영역)
. 90% 이상을 Zone 5 (무산소)
라고 한다.
존 2 (Zone 2)
심박수를 존 2 영역에서 계속 머무르면서 하는 운동을 존 2 훈련이라고 하는데, 사이클이나 러닝에서 많이 적용되며 일반인뿐만 아니라 엘리트 운동선수들도 기초체력 강화를 위해서 존 2 훈련을 사용한다.
심박수는 개인별로 워낙 편차가 커서 정확하게 알기 어렵지만, 참고용으로 가장 간단한 공식은 다음과 같다.
Zone 2 심박수
= 최대 심박수의 60% ~ 70%
= (220-만 나이) x 0.6 ~ 0.7
참고로 본인이 평소에도 체력이 좋다고 생각하면 위 공식보다 + 10 정도 해도 되고, 반대로 체력이 약한 경우 -5 ~ -10 정도로 봐도 된다. 사실 공식 자체도 개인별 특성이 전혀 반영되지 않고 그저 나이만 입력하기 때문에 대략적인 범위만 참고하는 것이 맞겠다. 그래서 내 몸이 느끼기에 정말 부담 없는, 옆사람과 계속 대화하면서 몇 시간이고 갈 수 있는 정도를 각자 찾는 것이 중요하다. (정말 부담이 없는 강도로 오래오래 움직이는 것이 핵심)
또 다른 공식으로 180에서 만 나이를 빼는 것을 상한선으로 해서 뛰는 것이다. 예를 들면 위와 같이 40세인 사람은 (180 - 40 = 140 bpm이 최대 유산소 심박수가 되고 따라서 그 사람은 약 130~140bpm 사이의 심박수에서 뛰면 된다.
사실 사람마다 체력 수준이 서로 매우 다르기 때문에 심박수는 참고 수치가 될 수는 있으나 절대적인 것은 아니라고 하니 각자 '오래 달려도 호흡이 편안한 강도'를 잘 찾아보자.
체력을 기르는 존 2 운동
축구 선수들도 고강도 인터벌이나 공을 다루는 연습 자체만큼 중요시하는 것이 이러한 저강도 유산소 훈련인데, 코치진들이 선수들에게 아주 천천히 힘이 안 들게 뛰는 슬로우 조깅을 매우 오래 시킨다고 한다. 실제로 이러한 훈련이 질주한 다음 잠깐 쉬는 사이에 빠르게 원래 컨디션으로 회복하는 능력을 키워 준다니 '덜 지치고 & 힘들더라도 금방 회복되는 것'이 나 같은 일반인이 원하는 '체력'의 정의에 가장 가깝지 않을까?
마라톤 선수들도 전체 훈련 시간의 80%는 존 2 달리기에 사용하고 나머지 20% 시간 내에서만 존 5까지 왔다 갔다 하는 인터벌 달리기나 시합용 스피드 연습을 한다니 그야말로 쉽게 설렁설렁 오래 달리는 것이 기초 체력을 다지는 방법으로 참고할 만하다.
존 2 영역에서 오래 저강도 유산소를 진행하면 세포 속의 미토콘드리아 수가 늘면서 지방을 태워서 에너지를 발생시키는 공장이 많아지는 셈이라서 몸 자체가 지방을 잘 분해하는 체질로 바뀌는 효과가 있다고 설명한다. 그리고 금방 소진되는 당(글리코겐)과 달리 지방을 사용하는 시스템이 발달해서 이전보다 더 오래가는 체력이 길러진다고 원리를 설명하고 있으니 참고하자.
그리고 운동의 방법이 꼭 달리기만 있는 것은 아니고 달리기나 자전거 외에도 수영이라든가 버피라든가 로잉머신 등 각종 운동을 심박수를 컨트롤하면서 하면 된다. 하지만 러닝이나 사이클처럼 같은 동작을 단순하게 반복하면서 세기와 속도를 조절하면서 심박을 제어하는 것이 쉬운 운동이 드물어서 보통 이 두 가지 종목으로 존 2 훈련을 하는 것 같다.
존 2 달리기 연습
그래서 약 2개월 전부터 이러한 존 2 달리기 연습을 하고 있는데 이게 처음에는 생각보다 쉽지 않다. 이미 숙련된 러너라면 모를까, 내 경험상 달리기를 시작한 지 몇 개월 안되었을 때에는 Zone 2는커녕 조금만 달려도 Zone 3~4를 가뿐하게 넘어선다. 그리고 일단 올라간 심박수는 아무리 천천히 달려도 Zone 3 이하로 내려오지 않는 경험을 하게 될 것이다. 그래서 결국 달리지 말고 걸어야지만 한참 뒤에야 Zone 2로 복귀한다.
이런 시행착오 끝에 현재 결론은 아래와 같다. (단, 심박수를 모니터링할 수 있는 가민/삼성/애플 워치나 밴드 종류를 사용하는 것으로 가정했다.)
(1) 러닝머신을 '(내 생각보다 훨씬) 느리게 걷는 속도로 세팅'하고 나서 제자리 뛰기 하듯이 달리는 것이다.
(2) 초보자는 몇 분만 달리기 폼을 취해도 심박수가 Zone 2를 넘어갈 수 있는데, 너무 실망하지 말고 Zone 기준을 넘어가면 그냥 걷자. 걷다가 심박수가 Zone 2의 하한선(작은 숫자) 근처까지 떨어지면 다시 살살 달려본다. 이른바 걷+뛰 전략이다.
(3) 계속 연습하다 보면 본인이 정한 시간을 (Ex. 30분~1시간) 걷기 없이 달리기로만 심박수 Zone 2를 유지할 수 있게 되면 러닝머신 속도를 0.1~0.2km/h 정도 더 올리는 것을 반복하는 것이다. (속도를 올리는 건 필수는 아니고 너무 느린 속도면 달리기 자세가 잘 안 나오기 때문에 달리기 자세 연습할 정도 수준까지는 올려보자는 취지이다.)
보통 건강한 성인이 걷는 속력/속도가 4~6km/h 정도 될 것인데 이 정도 느린 스피드에서도 처음 해보는 사람은 몇 분만에 심박수가 많이 올라갈 수 있다. 심박수가 올라갈 때 이를 낮추기 위하여 러닝머신 속도를 2~3km/h 수준으로 확 더 낮추는 방법도 있지만 심박 변화가 잦기 때문에 심박에 따라서 러닝 머신의 속도를 조절하기가 쉽지도 않고 달리기 자세 연습에도 방해가 되니 평소 걷는 속도보다 좀 더 느리게 세팅하고 걷기+뛰기를 반복하는 방법을 추천한다.
30분 이상 zone 2에 머무르면서 (걷지 않고) 달리기 자세를 유지하는 것이 첫 번 째 목표다.
존 2 달리기와 함께 인터벌 달리기
그리고 위에도 언급했지만 유산소 운동의 80%의 시간을 존 2 달리기에 썼다면 나머지 20%는 인터벌 훈련을 해서 최대 퍼포먼스가 나오도록 하는 것이 좋다. 심박수를 최대 심박수 (Zone 4~5)까지 근접하게 올렸다가 짧은 휴식 동안에 Zone 2 근처까지 끌어내리는 것을 3~5회 반복하는 것이 인터벌 훈련을 매우 단순하게 설명한 것인데, 인터벌도 각양각색의 방법이 있겠지만 아래와 같이 간단한 연습 방법을 제안한다.
Example)
웜업 5분 정도 조깅 후, (질주 4분 + 걷기 or 슬로우 조깅 4분) × 4회 반복 = 총 37분 소요
질주하는 동안 심박계(시계)를 쳐다볼 틈은 없을 것이니, 타이머 앱을 활용하여 4분마다 알람이 울리게 해서 질주와 걷기를 반복하면 신경을 덜 쓰고 할 수 있다.
진정한 의미의 '전력' 질주로는 아마도 4분을 버티기는 힘들 테니, 평소 목표하던 달리기 페이스가 있다면 그것보다 좀 더 빠른 것을 질주의 스피드로 삼으면 적당할 것이다. 목표는 질주하는 구간 마지막쯤에는 최대 심박수의 90%를 넘어보는 것이다.
80:20 비율을 맞추려면..
일주일에 4일 달리기를 한다면 3일은 50~60분짜리 존 2 달리기를 해주고, 하루는 40분짜리 인터벌을 해주면 대략 비율이 맞는다.
만약 주 3일 달리기 계획이라면 (예를 들어 화/목/토) 화요일에 60분 존 2 달리기, 목요일에 40분짜리 인터벌, 토요일에 2시간짜리 존 2 달리기를 해주는 식이다. 다시 말하지만 존 2 달리기는 '너무 쉬워서 1~2시간 정도는 움직일 수 있는' 운동 수준이어야 한다. 처음 시작하는 사람들은 1~2시간 동안 총총걸음 또는 걷+뛰 수준의 산책이라고 생각하자.
인터벌을 더 짧고 굵게 20분 만에 끝낸다면 화/목/토 주 3일 달리기로 화요일 30분 존 2 달리기, 목요일 20분 인터벌, 토요일 1시간 존 2 달리기... 이런 식으로 할 수도 있겠다.
힘 안 들이면서 지방 태우는 가성비 운동 ‘존투’
힘은 안 들이면서 심폐지구력은 높이고 체지방은 뺄 수 있는 방법이 있다. ‘존투(Zone 2) 운동’을 하면 된다.
운동 강도는 최대심박수를 기준으로 다섯 구간으로 나눌 수 있다. 최대심박수의 ▲50~60% ▲60~70% ▲70~80% ▲80~90% ▲90~100%다. 존투 운동은 말 그대로 두 번째 구간(최대심박수의 60~70%)에 해당하는 운동을 말한다. 옆 사람과 대화를 나누면서 운동할 수 있는 정도의 강도로, 비교적 가볍고 편안하게 운동할 수 있다.
신체 부담은 덜한데, 효과는 좋은 가성비 운동이다. 특히 심폐지구력을 키우는 데 좋다. 존투 구간에서 우리 몸은 산소를 이용해 에너지를 생산하는 대사 활동을 한다. 이 대사는 세포 속 미토콘드리아에서 이뤄진다. 존투 운동을 할수록 미토콘드리아의 숫자와 에너지 생산 능력이 좋아진다. 심폐지구력이 높아져 긴 시간 지치지 않고 운동할 수 있게 된다. 미토콘드리아 숫자가 증가하면 면역력이 높아지고, 노화 속도도 늦출 수 있다고 알려져 있다. 세 번째 구간 이상에서는 나타나지 않는 효과다.
게다가 존투 대사 활동의 주재료는 지방이다. 30분 이상 존투 운동을 하면 효과적으로 체지방을 태울 수 있다. 건강관리 통합 플랫폼 콰트의 김하정 운동지도사는 "존투에서는 공급받는 산소량과 소모하는 산소량이 일치해 힘들지 않게 오래 운동할 수 있다"며 "미토콘드리아가 증가할수록 지방 소비 효율도 올라가, 살이 잘 빠지는 체질로 바뀔 수 있다"고 했다.
부상 위험이 낮고, 고강도 운동보다 지속할 수 있다는 장점도 있다. 정신 건강에도 좋다. 몸이 긴장하도록 하는 교감 신경 활성화를 완화해, 명상 효과를 준다. 존투 운동 효과를 제대로 보고 싶다면 최소 30분은 운동해야 한다.
존투 운동에 해당하는 심박수는 어떻게 계산할 수 있을까? 최대심박수는 사람마다 다르다. 정확한 측정값은 운동 부하 검사로 재야 해, 가정에서 확인하기 어렵다. 대신 계산식을 활용해 추정할 수 있다. 가장 쉬운 수식은 220에 만 나이를 빼는 것이다. 만 서른 살이면 220에 30을 뺀 190이 최대심박수인 식이다. 이 값에 0.6~0.7을 곱한 값인 114~133이 존투에 해당한다. 다만, 이 수식은 개인 체력 수준을 반영하지는 못한다.
더 정확한 최대심박수와 목표심박수를 알고 싶다면 카보넨 공식을 이용하면 된다. 개인 체력 수준을 반영할 수 있는 여유 심박수로 계산할 수 있다. 여유심박수는 최대심박수에 도달하기까지 남는 심박수를 말하는데, 앞서 계산한 최대심박수(220-나이)에서 편안할 때 잰 심박수인 안정시심박수를 빼면 된다. 존투에 해당하는 심박수는 여유심박수에 0.6~0.7을 곱한 뒤, 다시 안정시심박수를 더하면 된다. 안정시심박수는 웨어러블 디바이스, 핸드폰 등을 이용해 확인할 수 있다. 검지와 중지로 귀 아래나 손목 안쪽에서 1분간 측정해도 된다. 계산 방법이 복잡하다면 카보넨 공식 계산기를 포털에 검색해 값만 넣으면 확인할 수 있다.
다만, 단시간 내에 체지방을 빼는 게 주된 운동 목적이라면 존포(Zone 4)에서 운동하는 게 낫다. 효율성만 보면 지방을 주연료로 사용하는 심박수에서 운동하는 게 낫지만, 같은 시간 고강도(80~90%)로 운동했을 때 절대적으로 소모되는 총열량은 더 많기 때문이다. 연소하는 지방량도 비례해 많아지고, 운동 후 쉴 때 심박수가 지방을 효율적으로 태우는 구간으로 내려가면서 지방이 더 타는 추가 효과를 볼 수 있다.
A Guide to the Biggest Thing Missing From Your Fitness Routine: Zone 2 Training
I knew I was supposed to do cardio because it’s good for my heart and insulin resistance and whatnot. So when I did do cardio, I found ways to make the experience as not sucky as possible.
The first prong of my “make cardio less sucky” strategy was to get it done quickly by doing short sessions of high-intensity training. I’d go hard — sprinting, “cycling” on the Airdyne, or doing burpees and calisthenics — for 15 to 20 minutes and call it a day. But I wasn’t that consistent with my HIIT. I’d aim to do it at the end of my weightlifting sessions, but when the time came, I often found an excuse to skip this planned cardio cap-off.
The other prong of my “make cardio less sucky” strategy was to ruck. I enjoy rucking. But honestly, I tend to sandbag it — metaphorically — when I ruck. I’m just taking a leisurely stroll with 40 lbs on my back. My heart rate hardly gets above 100 beats per minute. I never feel like I’m really “exercising.” It’s better than doing nothing, certainly, but probably leaves a lot of the benefits of cardio on the table.
So, for all intents and purposes, the cardio portion of my exercise routine had been pretty non-existent.
But after my conversation with hybrid athlete Fergus Crawley on the AoM podcast, I’ve started to make cardio — in particular, slow and steady cardio — a bigger part of my life. And it’s all because of what he said about “Zone 2 cardio” and the benefits he’s seen it give him in his own life in terms of both his mental health and his strength-training performance.
Below I share what I’ve learned about Zone 2 cardio since that show. We’ll get into what Zone 2 cardio is, what it does for you, and how to make it part of your life.
What Is Zone 2 Cardio?
To understand what Zone 2 cardio means, you first have to understand how your body uses the food you eat to power your existence.
All cells in your body are fueled by adenosine triphosphate or ATP. When you walk, you’re using ATP. Deadlifting? Powered by ATP. Reading this article? ATP.
ATP can be produced in three ways:
Through oxygen-dependent metabolism that utilizes fatty acids (oxidization). This is how most of the ATP you use throughout the day is created. When you breathe, oxidation turns fatty acids into ATP. Oxidation creates a lot of ATP. You get a lot of bang for your buck. Oxidation occurs within your cells’ mitochondria. This is an essential point for Zone 2 cardio.
Through non-oxygen-dependent glucose metabolism (glycolysis). If you’re doing an intense exercise like sprinting or lifting weights, your body switches from oxidizing fatty cells to produce ATP to burning glycogen/carbs to replenish ATP stores. Glycolysis produces large amounts of ATP, but not as much as oxidation. Glycolysis doesn’t occur in your mitochondria but rather in your cells’ cytosol.
Through the recycling of previously-stored ATP. When ATP transfers energy to cells, it breaks off one of its phosphates and becomes adenosine diphosphate (ADP). Creatine then comes along and says, “Hey, ADP, you can have my phosphate,” turning it back into ATP to once more be utilized as energy. Creatine supplementation can help this process.
Note: we can also get ATP from lactate. Basically, our body can convert lactate into glucose to be used in glycolysis. It’s fascinating but pretty technical. You can learn more about this process here.
Over the years, exercise scientists have developed “training zones” to help athletes and coaches understand which energy systems and muscle fibers they’re using at a given exercise intensity level.
One such system divides training intensity into six zones. Zone 1 is the lowest intensity (sitting down, walking around your house, etc.), and Zone 6 is the highest intensity (all-out sprinting, deadlifting a heavy set of five, etc.).
Zone 1
Energy source mainly used: fat
Zone 2
Energy source mainly used: fat trending into carbohydrates
Zone 3
Energy source mainly used: fat trending into carbohydrates
Zone 4
Energy source mainly used: carbohydrates
Zone 5
Energy source mainly used: carbohydrates
Zone 6
Energy source mainly used: carbohydrates trending into creatine phosphate
As you can see, the type of fuel your body uses to create ATP changes as you go up in intensity. In zones 1 and 2, you’re using primarily fat. As you shift to Zone 3, you start using carbohydrates. When you reach zone 6, you use creatine phosphate to create ATP.
In Zone 2, your exercise intensity is at a level in which you are stimulating your cells’ mitochondrial function the most. You can meet your body’s demand for ATP using only fat and oxygen in your mitochondria. If you were to go a bit harder, your body would start using more carbs in your cells’ cytosol to create ATP through the process of glycolysis.
According to Dr. Iñigo San Millán, an expert in exercise physiology and sports medicine, most recreational athletes don’t spend a lot of time in Zone 2. Instead, they usually skip to zones 3, 4, and 5, where they primarily use carbs as their fuel source. He attributes this to the emphasis on high-intensity training over the past decade. When a lot of people start working out, they’ll do something like P90X or CrossFit — if not those exact programs, then a workout that includes the same kind of form and intensity. We have this idea that if exercise doesn’t feel painful and uncomfortable, it’s not doing anything.
We also jump right past Zone 2 because it’s simply really easy to do, unless you intentionally try to dial back your effort. When you go out for a jog, you probably run at a pace that isn’t a sprint, but does leave you huffing and puffing. This feels like a “normal” pace to you, but you’re almost assuredly in Zone 3 or higher.
Unlike the way most people typically do their cardio, Zone 2 doesn’t feel painful or uncomfortable. In fact, you could probably move at that intensity for hours at a time.
This is why people skip over Zone 2. It’s deceptively easy.
But according to a lot of research, you’re missing out on many health and performance benefits by giving Zone 2 cardio the short shrift.
The Benefits of Zone 2 Cardio
Increases the number and efficiency of mitochondria in your body. Zone 2 is the level at which you’re stimulating your mitochondria the most to create ATP. As you spend more time in Zone 2, your body will respond by creating more mitochondria to power your Zone 2 activity. The more mitochondria you have, the more you’re able to create ATP through fat oxidation. And remember, your mitochondria can make a lot of ATP.
Zone 2 training not only increases the number of your mitochondria, but improves their efficiency as well. The more you exercise in Zone 2, the better your body gets at burning fat for energy. The body’s inefficiency at using fat for fuel contributes to many health problems like insulin resistance, dementia, and even cancer. Basically, if you want to move better, have more energy, and live longer, you want to exercise a lot in Zone 2.
Improves your performance as an endurance athlete. If you’re a runner or cyclist, spending more time in Zone 2 will allow you to go faster for longer. Zone 2 cardio has been used for decades by elite athletes. As I discussed in my podcast with running coach Matt Fitzgerald, one of the things that separates professional runners from amateurs is that the latter spend about 80% of their workout time in Zone 2. In contrast, the weekend warrior runner will spend most of his time in zones 3 and 4. Pros go slow (relative to their fitness, of course).
What’s counterintuitive about spending more time in Zone 2 during your runs and rides is that while it doesn’t feel like you’re going that hard, it does make you a better athlete. You are able to go progressively faster and longer, while your heart rate remains low. As you train your body’s ability to use fat for fuel, you’ll be able to increase your pace without shifting over to carb-burning. And because you’re using fat, you’ll be able to go faster for longer because you have a nearly unlimited supply of fat.
Kate has been doing Zone 2 cardio for six years now, ever since hearing primal-living guru Mark Sisson talk about the idea on the podcast. She’s noticed that even though the bulk of her running workouts are “easy,” her finish times in races are significantly better than they ever were, even in her younger years. That’s the paradox of Level 2 cardio: you go slow, to go fast.
Improves cardiovascular health. Besides exercising your mitochondria, Zone 2 cardio also gives your heart and blood system a workout. Your heart will get stronger and will require fewer pumps to pump blood; it will become more efficient. Your body also expands its vascular system, better enabling it to deliver oxygenated blood to the different parts of your body. This improvement in cardiovascular fitness will result in better performance when exercising as well as a lower resting heart rate. An average adult’s resting heart rate is 60-100 bpm. Kate’s resting heart rate is around 40 bpm. Mine is in the low 60s (that’s what I get for being a late adopter!). I’m hoping it will decrease further the longer I stick with the Zone 2 habit.
Improves work capacity. This is of interest to me as a strength athlete. Zone 2 cardio can help you recover more quickly between lifting sets which in turn can allow you to do more work in a training session. I’ve noticed that I’ve gotten less winded during my barbell sessions as I’ve added Zone 2 cardio to my routine. I just feel like I can get everything I need done during my one-hour workout.
Prevents injury and aids recovery. Zone 2 stresses the body very little. It thus enables you to add volume to your training routine without getting sidelined by injuries or fatigue. Even after doing a long session of Zone 2 cardio one day, you’ll be ready for another the next.
Zone 2 cardio also serves as great “active recovery exercise.” When you’re in Zone 2, you get the blood pumping, which delivers nutrients to your muscles to help them bounce back from a weightlifting session. My physical therapist recommended that I do some Zone 2 training to help my recovery from tennis elbow and an issue with my knee. “It helps get some blood there to help heal things,” he told me, and it indeed seems to work.
Boosts mood. Fergus mentioned how he’s noticed that his mood has gotten better as he’s incorporated Zone 2 cardio into his fitness routine. I’ve noticed these mood-boosting benefits as well. Probably because you’re getting the muscles moving and blood flowing, but aren’t severely stressing the body, Zone 2 cardio generates plenty of feel-good endorphins. It just feels fantastic.
How to Determine If You’re in Zone 2
To exercise at optimal Zone 2 intensity, you want to be exerting yourself at a level where you’re primarily using fat oxidation to power your movement and maxing out mitochondrial function, without switching into burning carbs; you want to butt right up against the boundary to Zone 3, without crossing over into it.
How do you know if you’re residing in this cardiovascular sweet spot?
There are several different ways to figure it out:
Heart Rate Method
The most common way people determine whether they’re in Zone 2 is by tracking their heart rate while exercising.
The idea is that our heart beats at a certain percentage of our maximum heart rate, depending on what zone of intensity we’re in.
When you’re in Zone 2, your heart beats at 70-80% of your maximum heart rate, more or less.
So if your maximum heart rate is 180, your Zone 2 heart rate would have a minimum threshold of 126 and maximum threshold of 144; the more you can stay around the 144 mark without exceeding it, the better.
But how do you figure out your maximum heart rate?
Do a max heart rate test. The best way to determine your maximum heart rate is to test it by running on a treadmill or cycling on a stationary bike. You start running and cycling and increase the speed every 2 minutes until you can’t sustain the pace any longer. Your heart rate at that moment is your maximum heart rate.
Estimate based on your age. If you don’t want to do a max heart rate test, you can estimate your maximum heart rate using your age. The formula is 220 minus your age.
So if you’re 30 years old, your maximum heart rate would be 190 (220 – 30 = 190).
70-80% of 190 would give you a Zone 2 heart rate range of 133-152, and you would want to stay as close to that 152 number as possible, without going over.
This method isn’t very accurate. Your max heart rate might be more or less depending on your fitness level, but this will at least get you in the general ballpark.
Maffetone Formula
Athletic performance coach Phil Maffetone was a pioneer of the “train slow to go fast” idea, having advocated this approach back in the 1980s. While he had plenty of critics over the decades, a lot of folks have now come around to, if not the exact formula he uses to get your Zone 2 heart rate, his general philosophy.
That formula, like the age-based equation described above, isn’t very accurate, but will get you in the Zone 2 ballpark.
The number the Maffetone formula gives you is the heart rate that will put you at the upper limit of Zone 2. The formula is as follows:
Subtract your age from 180, then modify based on the categories below:
If you have or are recovering from a major illness (heart disease, any operation or hospital stay, etc.), are in rehabilitation, are on any regular medication, or are in Stage 3 (chronic) overtraining (burnout), subtract an additional 10.
If you are injured, have regressed or not improved in training or competition, get more than two colds, flu, or other infections per year, have seasonal allergies or asthma, are overfat, are in Stage 1 or 2 of overtraining, or if you have been inconsistent, just starting, or just getting back into training, subtract an additional 5.
If you have been training consistently (at least four times weekly) for up to two years without any of the problems mentioned in a) or b), no modification is necessary.
If you have been training for more than two years without any of the problems listed above and improved competitively, and are without injury, add 5.
So if you’re 40 years old, the upper limit of your Zone 2 heart rate using this formula would be 140, more or less.
Talking Test
The easiest (and yet still surprisingly accurate) way to determine if you’re in Zone 2 is to do the “talking test.” When you’re exercising in Zone 2, you can comfortably have a conversation, but will still sound a little breathy; you’re not able to talk as clearly as when you’re at rest, but you’re still capable of talking.
Physician and health/performance guru Peter Attia has the best description of what this feels like. He says when he’s in Zone 2, he can comfortably have a conversation with someone on the phone for hours, but the person on the other end of the phone would notice that he was exercising.
Personally, how I determine if I’m in Zone 2 is a combo of the Maffetone formula and the talk test. I use the Maffetone formula to figure out roughly where my Zone 2 heart rate is. I’ll work up to that heart rate and then use the talk test to refine my intensity.
Measure Your Lactate
The most accurate way to determine if you’re in Zone 2 is to measure your lactate after your training session. If your lactate is between 1.7 and 1.9 mmol, then you were in Zone 2.
The downside of this method is that you have to stick yourself to get a drop of blood for the test. That’s annoying. Also, the test strips are expensive — like $4 a pop.
This method is for the people who really want to geek out on this.
How to Get Your Zone 2 Cardio
You can get your Zone 2 cardio however you want. If you like to run, run. If you like to bike, bike.
You could even do Heavyhands or rucking, if you sufficiently push yourself to get your heart rate up to the right zone.
Regardless of what exercise modality you choose to get your Zone 2 cardio, the tricky part about this kind of training is consistently keeping your heart rate within its parameters. You want your heart rate to pass from Zone 1 and into the upper strata of Zone 2, but not rise into Zone 3 — which is an easy jump for it to make, even when you’re not pushing yourself very hard.
Let’s say you start jogging right now. Your heart rate will likely surge way above your Zone 2 target. You then have to start walking to bring it down. At which point it falls below your Zone 2 threshold. So you start jogging again. And your heart rate once more jumps past your Zone 2 upper limit. So you start walking again. Your workout ends up being a series of frustrating fits and starts.
For this reason, full-body, high-exertion exercises like running and swimming are hard ways to do Zone 2 cardio, at least when you’re first getting going with it. Look to do less taxing forms of cardio instead. Since cycling only uses half your body, it’s a good option. So is using cardio machines like the elliptical. Or crank a treadmill up to its highest incline and take a walk. In our experience, using a special incline treadmill, where you can set the incline all the way to 30-40 degrees (a standard treadmill tops out at 15 degrees) and then walk while holding onto handles, is especially good for getting your heart rate high-but-not-too-high, and offers the perfect, highly satisfying Zone 2 workout.
Whichever cardio machine you choose, the benefit of using one is that you can set a very steady pace/resistance/incline (without sudden heart-rate-spiking hills) which will allow you to consistently stay in Zone 2. Start each workout slowly, as your heart rate has a tendency to spike when you first initiate exercise, and, as long as you’re keeping your warm-up nice and easy, don’t worry too much if your heart rate spikes some during the first 5-10 minutes of your training session; it takes awhile for your heart to settle into a steady state rhythm, which is why, as we’ll discuss below, it’s recommended that every Zone 2 session be a minimum of 45 minutes long.
It’s possible and desirable to eventually do your Zone 2 runs out of doors. As Fergus told me, it’s the combination of Zone 2 cardio + nature that has most helped his mental health. With high intensity exercise, and its attendant spike in heart rate, your higher-level thinking starts to shut down. With Zone 2 training, the engaged-but-near-automatic movement pattern of your run keeps your body occupied, while your mind remains unstressed and clear; it’s a great way to find flow. Fergus says it’s his version of zen. Even though he’s out there for hours at a time, he trains without headphones, as he loves the opportunity to switch off and let his mind wander as he runs for mile after mile through fields and along rivers. In fact, he makes a list of things he wants to think about before he heads out, giving himself prompts as what he’d like to reflect on as he runs. You may find that your outdoor Zone 2 training sessions become your best brainstorming times. Kate often receives and refines Sunday Fireside ideas while she’s out trail running.
If you want to do outdoor Zone 2 runs, without having to run 15-minute miles and move in walk/jog fits and starts, first build up your Zone 2 fitness base by walking on an incline on the treadmill. This obviously isn’t the same as running, but it will improve your cardiovascular fitness using a similar movement pattern to running.
Next, start jogging on a flat/non-inclined treadmill. You should be able to stay in Zone 2 by running at a slow pace, like 5 miles per hour. As your training progresses, increase your pace while staying in Zone 2. You should be able to run progressively faster, while keeping your heart rate in the same place.
Once you’ve built a solid Zone 2 training base on the treadmill, take your running outside, starting by running a flat course (no hills). Once you can run a flat course while staying in Zone 2, you can start running a route that includes hills. No matter how fit you get, though, there may be hills you’re never able to ascend while staying in Zone 2 without walking up them.
How Much Zone 2 Cardio Do You Need?
There are a lot of numbers thrown around as to how much Zone 2 cardio you need each week.
Based on all the articles and podcasts I dived into, 150 to 180 minutes a week of Zone 2 cardio is a good number to shoot for as a minimum.
According to Dr. Iñigo San-Millán, to get the full benefits of Zone 2 cardio, you want your sessions to be at least 45 minutes long. That seems to be the minimum effective dose to get the mitochondrial benefits of Zone 2 training.
So if you’re aiming to do 180 minutes of Zone 2 cardio a week, you could do four 45-minute weekly sessions, or you could do your 180 minutes in one very long session. Find what works for you.
Personally, I’ve been doing three 60-minute sessions a week. That works for me.
60 minutes is a pretty long time to be slowly spinning along on an elliptical. To make my Zone 2 cardio something I look forward to, rather than avoid, I’ve done some temptation bundling with it and watch movies and TV shows while I work out. Right now, I’m rewatching 30 Rock during my Zone 2 sessions. Three episodes will get me through an hour of Zone 2 cardio, and as someone who doesn’t watch any television outside of exercise hours, this makes the workout feel like a treat.
While the above is ideal, San-Millán is quick to point out that any amount of Zone 2 cardio is better than none. If you can’t squeeze in 180 minutes a week, then get what you can. Don’t let the perfect be the enemy of the good!
Finally, while Zone 2 cardio should make up the majority of your cardiovascular exercise — 80% is a good proportion to aim for — doing a small amount of high intensity cardio is still important for health, fitness, and athletic performance. One weekly HIIT session, where you go all-out, should do it.
What you don’t want to be doing is spending all your time in what Attia calls the “garbage zone,” where you’re not exercising at a high enough intensity to improve your anaerobic fitness, and you’re not exercising at a low enough intensity to improve your aerobic fitness. Get out of this all-too-typical no-man’s-land of exercise! Really push yourself when you push yourself, and the rest of the time, take up residence in the slow-and-steady, health-wonder-working Zone 2.
Take a deep dive into the ins and outs of Zone 2 cardio in this podcast interview I did with Alex Viada:
Zone 2 Resources to Check Out
If you’d like to learn more about Zone 2 training, I highly recommend listening to these two podcasts with Peter Attia and Iñigo San-Millán. They take a deep dive into what’s happening in your body with Zone 2 training, the benefits, and how to measure it. They were a really useful resource for me as I learned about Zone 2 cardio. Really fascinating stuff!