Milroe had 75 total touchdowns over the last two seasons as Alabama’s No. 1 QB.
January 2025
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Nobody Can Agree on What ‘Zone 2’ Cardio Is
This post is part of Find Your Fit Tech, Lifehacker’s fitness wearables buying guide. I’m asking the tough questions about whether wearables can really improve your health, how to find the right one for you, and how to make the most of the data wearables can offer.
“Zone 2” is the term the fitness world has (mostly) agreed upon to describe the low intensity cardio most of us should be doing regularly. When you’re in zone 2, you’re working hard enough that you start breathing more heavily, but easy enough you could hold a conversation doing it. You stop a zone 2 session because your workout time is up, not because you’re too exhausted to continue.
But what heart rate should you expect to see on your fitness smartwatch when you’re in zone 2? That’s where people disagree.
What is zone 2 training?
As I’ve explained before, the name “zone 2” comes from heart rate training. To train by heart rate, you use either a wristwatch with an optical heart rate sensor (that green light on the back) or a chest strap paired to your watch or just to a phone (chest straps are more accurate, and I recommend a good $25 one here).
To train by heart rate, you aim to keep your heart rate in the “zone” that gives you your desired workout. In most of the popular systems, there are five zones. Zone 1 is your resting or recovery zone; zone 2 is low intensity cardio; and zones 3, 4, and 5 are for harder efforts, usually done for only a few minutes with recoveries in zone 1 or 2 in between. (I have a more detailed guide to the zone system here.) While zone 2 is the trendiest at the moment, the other zones still have uses. Personally, I think zone 3 is underrated, and probably most of us would be better off getting a mix of zones 2 and 3 for our steady cardio rather than pure zone 2. But that’s a story for another time.
Heart rate zones are usually defined as percentages of your maximum heart rate. So when I set my Apple Watch to keep me in zone 2 during my runs, it wants my heart rate to be between 60% and 70% of maximum. Even at an easy effort, I found I was commonly exceeding that limit. On the other hand, when I hop on a Peloton bike, my heart rate is often still in zone 1 when I could swear I’m riding at a zone 2 effort. It turns out that system defines zone 2 as 65% to 75% of my max.
Who is right? Well, everybody. “Zone 2” isn’t a term with scientifically designed boundaries. Anybody can split up heart rate zones any way they like. (Stay tuned for my patented eight-zone system, coming as soon as I can find a way to monetize it!) If you train with more than one gadget, or if you find yourself discussing heart rate training with a friend who uses a different system than you do, it’s worth knowing the differences.
What heart rate percentage counts as zone 2?
Let’s take a tour of some of the more popular wearables and fitness systems that measure heart rate in a five-zone system, or something like it.
First, it’s important to know that most (not all) of these percentages are based on your max heart rate. To know your max heart rate, you need to do a real-world test, not just calculate it from a formula. For example, one formula calculates my max heart rate as 178 beats per minute, and another says it should be 169; in reality, I’ve seen as high as 207 when I’m running, and 198 on a spin bike. (And yes, your max can differ for different types of cardio. My heart rate while I’m swimming would probably be lower still; when your body is horizontal, your heart has an easier time moving your blood around.)
There are other systems to consider too. “Heart rate reserve” (HRR) means that you take the difference between your max and your resting heart rate (instead of between your max and zero) and calculate from there. Some gadgets will estimate a different benchmark, like your lactate threshold, and use that as a basis for the zones.
So, here are the zone 2 percentages from a variety of popular wearables, along with what they are percentages of:
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Apple Watch: Zone 2 is 60-70% of your heart rate reserve, with your “resting” heart rate set to either 72 or a number the watch has picked up automatically, and your maximum calculated with the 220-age formula. (You can choose to set the zones manually, instead.)
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Fitbit: instead of “zone 2,” Fitbit devices have a “moderate” zone (formerly called “fat burn”) set at 40% to 59% of your heart rate reserve. To find your heart rate reserve, your max is calculated according to the “220 minus age” formula, and your resting heart rate is measured by the device. You can set your max and your zones manually if you prefer.
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Garmin: Depends on your device and on how you’ve chosen to set up your zones. As a percentage of max heart rate, zone 2 is 73-81%. As a percentage of heart rate reserve, it’s 65-75%. And as a percentage of your lactate threshold heart rate (which the watch can automatically detect for you, and which normally falls between zones 4 and 5), it’s 79-88% of that heart rate. Note that these numbers won’t necessarily line up with each other. A heart rate that is in zone 2 on one of these systems may be in zone 3 on another. And, of course, you can set your max and/or your zones manually.
Some other fitness platforms have defined heart rate zones to be used with your training. To name a few:
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Orangetheory gets its name from the “orange” zone it wants you to be in during workouts. Its equivalent of zone 2 would be the “blue” zone, at 61% to 70% of max heart rate. It uses an “industry standard formula” to determine your max, which Self reports is 208 minus 0.7 times your age. After you’ve taken 20 classes, an algorithm will pick out a new max heart rate for you.
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Peloton defines heart rate zone 2 (no relation to Power Zone 2) as 65% to 75% of your max heart rate. Max heart rate is 220 minus your age unless you adjust it manually in your settings.
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The American College of Sports Medicine defines “light” training, arguably its version of zone 2, as 57% to 63% of maximum heart rate. “Moderate” is 64% to 76%.
How do you know which benchmark to use?
Rather than obsessing over numbers, think about the big picture and decide what training effect you are trying to achieve with your workouts.
If you want to build your endurance with low-intensity cardio, or if you want to rack up minutes in this zone to help with weight loss, it doesn’t matter exactly what your heart rate works out to be. What matters is that you can do the exercise for a long time without fatiguing, but that you’re also not slacking off and barely doing any work at all.
In other words, you can use your gadget’s heart rate numbers as a guide, but keep them honest with a reality check based on what fitness professionals call “perceived exertion.” If you want a number to focus on, you can rate your exertion on a scale of 1 to 10—called RPE for “rating of perceived exertion”—and aim for an RPE of about 3 to 4.
Over time, you’ll start to notice what heart rate tends to show on your watch when you’re at that level. I know that if my heart rate is in the 150s, I’m doing a good job of keeping my jogging to a “zone 2″ sort of effort. If it pokes up into the 160s at the beginning of a run, that’s probably harder than I’m going for—but if it hits 160 at the end of a long run on a hot day, that’s fine. (Heart rate changes with the temperature and the length of your workout, a phenomenon called cardiac drift.)
Ultimately, this is probably the most accurate way of using heart rate to determine exercise intensity: figure out the intensity you want first, and use heart rate as a guide to be able to hit that same intensity on a consistent basis. After all, if there were one correct number that was easy to determine, the different gadgets and platforms would have all gotten on board with it by now. So trust your body more than your watch.
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How Much Exercise Do You Really Need?
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You probably know zero exercise is not enough and that going for a walk every day is generally a good thing. And if you’re training for a marathon, you’ll be on your feet for a couple hours of hard workouts every week. But what is the benchmark for a human being just trying to squeeze enough healthy exercise into their life? Let’s break it down.
The basics: 150 minutes of cardio and two days of strength training every week
Fortunately, all the major public health organizations are in agreement. The World Health Organization, the Centers for Disease Control and Prevention, and the American Heart Association are all on board with the following guidelines for aerobic exercise:
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At least 150 minutes per week of moderate intensity (cardio) exercise like walking or easy jogging, or 75 minutes per week of vigorous exercise like running, or a combination. (If you can easily meet that, more is better.)
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At least two days per week of muscle strengthening activity, like lifting weights or doing other strength training like pushups, resistance band exercises, or even heavy manual labor like shoveling.
A previous edition of the guidelines said that you need to do your cardio for a minimum of 10 minutes at a time for it to count, but the current recommendation is to get it in however you can, even if that includes some shorter bursts here and there.
If that’s too easy, level up to 300 minutes
If you’re pretty athletic, the above won’t sound like much. Good news! The WHO has set a secondary goal for folks like you. It’s simple: just do double the above. So you can aim for 300 minutes of moderate cardio, or 150 minutes per week of vigorous activity. Here’s what that might look like:
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An intense, hour-long martial arts class three times a week (60 x 3 = 180, but this is vigorous cardio, so the minutes count double)
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Go on a 45-minute after-dinner walk every day (45 x 7 = 315 minutes of moderate cardio)
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Commute by bike to work, 20 minutes each way (40 minutes per day x 5 days per week = 200 minutes moderate cardio) and play recreational league soccer for two matches per week (50 minutes each game, for some combination of moderate and vigorous cardio, definitely puts us over 300).
What do “moderate” and “vigorous” exercise mean?
Walking at a purposeful pace counts as “moderate” cardio, and jogging counts as “vigorous.” I have a detailed breakdown here of what exercises count as moderate versus vigorous. The distinction is not based on heart rate or effort level, but rather on a scientific metric called METs that relates to how much energy and oxygen the exercise takes. Moderate exercise is anything that scores between 3 and 6 METs, and vigorous exercise is 6+ METs.
That said, you can estimate by effort level. When you’re doing moderate exercise, you’ll be a little bit sweatier or breathing a little harder than when you’re at rest, but you can do it continuously without feeling tired. It may not even feel like a workout. Here are some examples of moderate cardio:
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Commuting or doing errands by bike, on relatively flat ground
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Using a spin bike or other cardio machines like the elliptical, at a low intensity, steady pace
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Housework and light yard work, like washing windows or mowing the lawn with a power mower
By contrast, vigorous exercise includes activities where you’re working hard and breathing hard. You might still be able to keep up a conversation, but it’s not likely to feel easy. Vigorous exercise also includes the really hard stuff where you might not be able to keep it up very long. This could include:
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Running fast
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Bicycling uphill
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Pushing yourself to finish a Crossfit WOD with a good time
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Swimming laps
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Playing a game of soccer or basketball
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Tougher housework and yard work, like chopping wood or using a push mower
Can I combine moderate and vigorous cardio?
You can mix and match these two intensities. The math is simple if you think about 150 minutes as your target and consider every minute of vigorous cardio counting double. Here are some examples:
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A 20 minute brisk walk every weekday morning (20 minutes x 5 days = 100 minutes moderate cardio) plus a 30-minute spin class that has you working pretty hard (30 minutes counted double is 60; add that to the 100 and you’re at 160 minutes).
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An hour of hiking, three days a week (60 minutes x 3 sessions = 180 minutes moderate cardio)
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Three 30-minute jogs (30 minutes x 3 = 90 minutes moderate cardio) plus a workout with 10 minutes easy jogging for a warmup and then 20 minutes of hard running, followed by a cooldown of another 10 minutes easy. (20 minutes vigorous x 2 is equivalent to 40 minutes moderate cardio, plus we can add the warmup and cooldown for another 20 moderate minutes). That gives you 150 total.
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Go for a 30-minute easy bike ride on Monday. Try a 45-minute water aerobics class on Wednesday. Take a short hike on Saturday. Mow the lawn for an hour on Saturday. (30 + 45 + 30 + 60 = 165 moderate cardio)
How much strength training do you need?
So far we’ve been talking about aerobic exercise, which is the kind where you’re continuously moving (or, perhaps, doing quick work/rest intervals) and your heart rate is up. But there are other important forms of exercise, too. The WHO and other organizations recommend two days per week of “high intensity muscle strengthening activity,” which includes anything where you’re thinking in terms of sets and reps. (Three sets of eight to 10 reps is a good structure to start.)
That activity can be anything that challenges your muscles, and where the last rep is a lot harder than the first. This could include lifting weights, or resistance band exercises, or bodyweight exercises like push-ups. So if you run three days per week and have time for more exercise, don’t just fit in extra runs; try adding two days in the weight room.
The strength training recommendations are for two days per week, per muscle group. If you like to work your upper body and lower body separately, that would mean two upper body days and two lower body days. If you prefer workouts that work all your muscles, you only need to do two of those full-body workouts per week (at minimum).
Can you get too much exercise?
What about an upper limit on how much exercise you get? There isn’t one, from a public health point of view. More is better. (And even if you are doing less than the recommendations, anything is better than nothing.) That said, it is always possible for you, as an individual, to do more exercise than your body is ready for. Don’t jump from a life of occasional strolling to a marathon training plan. (And if you are on that marathon training plan and you’re feeling worn down, take a break already.)