Zone 2 Training Can Boost Your Cardio Fitness — Here’s How to Do It

Training for your first distance race? Just looking to improve your health so you can live better, longer? Zone 2 training is being touted everywhere lately as the best option for optimizing just about every facet of your health and wellbeing. But is it really the type of exercise you should be focusing on?

In the world of endurance sports, overall health and longevity, it feels like every coach, doctor and podcast host is going off about zone 2 training.

"We tend to swing back and forth on a pendulum," elite performance coach Steve Magness author of ‌Do Hard Things: Why We Get Resilience Wrong and The Surprising Science of Real Toughness‌, says. "For a while, it swung to 'We need some intensity!' and everyone was talking about HIIT training. Now people are going back to the other thing — which is zone 2 training."

Aaron L. Baggish, MD, director of the Cardiovascular Performance Program at Harvard Medical School, agrees. "Zone 2 is nothing new," he says. "But many people are finally realizing they can 'get in their cardio' at an intensity that is pleasurable and simultaneously beneficial — both for health and athletic performance."

We've broken down what zone 2 training is all about and the best ways to put it into practice in your own workout routine.

The definition of zone 2 training depends on who you ask. Generally speaking, zone 2 training is aerobic or steady-state cardiovascular training, according to the National Academy of Sports Medicine (NASM). Some experts will say zone 2 is 80 percent of your maximum heart rate, or for cyclists, 80 percent of your maximum power output. Others will say it's 60 to 70 percent of your maximum heart rate or power output.

"Strictly speaking in the world of applied exercise physiology, we stay away from the use of numbered zones," Dr. Baggish says. "But zone 2 typically refers to workloads done below the first ventilatory or lactate threshold. Work done at this intensity is sustainable for long periods of time, and represents what most athletes would consider base building."

For recreational exercisers, this level of exercise provides substantial health benefits with minimal risk, Dr. Baggish says, while for competitive athletes, most of their training will be done at this intensity level.

"[Elite athletes] do this because they and their coaches realize that 'slow' training, when coupled with the right amount of 'fast' training — aka less time, but more intense — translates into better race performance," Dr. Baggish says.

Doctors and medical professionals are typically referring to something a little bit different. Zone 2 in this sphere is focused more on metabolic and cellular health, and it is defined as the highest metabolic output that you can sustain while keeping your lactate level — an acid produced by your muscle cells — below a certain level (two millimole per liter, which can only be determined by specific tests).

A quick biology primer: Right now, your cells are busy at work converting glucose (aka sugar) into energy using oxygen. That's called cellular respiration, and it happens pretty much 24/7, using the food you eat to help create the energy your body needs to live.

When exercising, that process picks up the pace. At higher intensities, there's not enough oxygen within the cell. The cell can still make the energy it needs, but it also produces a by-product called lactic acid, or lactate, which is released into your blood. Basically, lactate levels in your blood help signal that your body has gone from aerobic exercise (utilizing oxygen) to anaerobic exercise (utilizing energy in the muscles).

"Any time you're undergoing cellular respiration, your body is basically converting glucose or fatty acids into [energy]," Peter Attia, MD, author of ‌Outlive: The Science & Art of Longevity‌, says. "That process can be done very efficiently with oxygen. But as the demand for [energy] gets higher, your body has to start making trade-offs and it has to start doing this process outside of the mitochondria. In doing so, one of the by-products of this is lactate. So we use lactate as a proxy for any time your body is exceeding the capacity of the mitochondria."

Dr. Attia explains that there can often be discrepancies between the definition he follows and the definition used when calculating zones on your heart rate monitor. Zone 2, by his definition, might actually put someone closer to zone 3 on their watch, for example.

It's important to remember that there's a lot of nuance between how people (specifically MDs and endurance coaches) talk about zone 2 training. "It's two different conversations talking about something similar," Magness says.

Adding zone 2 training (i.e., steady-state cardiovascular training) to your routine can support your health and improve your performance, while lowering your risk of training-related injuries. These are the benefits often cited by medical professionals and doctors.

A June 2019 review in ‌Oxidative Medicine and Cellular Longevity‌ found that zone 2 training increases mitochondrial size, number and function. This means more efficient workouts and better overall health, Dr. Attia says.

Too much buildup of lactate in your bloodstream at one time is thought to be one of the reasons you feel fatigued after a workout. A very small June 2013 study in the ‌Journal of Applied Physiology‌ found that, in 12 men, regular endurance training improved lactate production, disposal and clearance.

While not much newer research has been done, a landmark October 2004 study in the ‌Scandinavian Journal of Medicine in Science‌‌ and Sports‌ found that keeping the majority of workouts in zone 2 helped increase performance and recovery.

The study was conducted with a small group of elite athletes who performed 75 percent of sessions below a lactate threshold of 2 mmol (or millimoles) — that's zone 2 — 5 to 10 percent of sessions in between 2 and 4 mmol, and 15 to 20 percent of sessions above 4 mmol.

For sports performance experts and coaches, the conversation around zone 2 is focused on the idea that you need a lot of easy training. Coaches find everyday athletes tend to push too hard on their easy days and not hard enough on their hard days, increasing their risk of injuries and overtraining.

"I think 'zone 2 training' as a term just came about as a way to help categorize a certain type of effort," Magness says.

When it comes down to it, zone 2 training is just sustained, easy effort. It's a great tool in your overall fitness toolbox and has a bunch of proven benefits. But stressing too much about what ‌exact‌ level of effort zone 2 is — or whether your heart rate is in precisely the right range — is not needed.

Not only is it tough to accurately gauge (you'd need to do regular blood testing to really know you're at the proper intensity), but training at zone 2 is not some miracle pill or solution.

The short answer: Yes. Very much.

"If we're looking at general fitness and improving health, then the best way to do it is to make sure you're getting a variety of stimuli so that your body keeps adapting and you're covering your bases," Magness says.

But that doesn't mean you want to evenly distribute your hard and easy days. "We're probably going to do more easy stuff — the lower zones — because it's easier, and we know because it's easier, it takes longer to adapt and grow from that," Magness says.

When it comes to the harder stuff (think: zone 4 or 5, or more than 80 percent of your maximum heart rate), you just need a little dose of it. If you were to do a series of short, all-out intervals on a bike or row machine, you're going to feel wiped out pretty fast.

"That's going to help you adapt to that pretty quickly — even after one workout," Magness says. "Why? Because it's hard. Your body goes 'Oh my gosh, this is a lot! It's like poison, I better adapt to this right away.'"

For well-rounded fitness, the volumes of the work will differ, but it's important to make sure there's a variety of intensities.

Like Dr. Baggish noted, most experts and coaches recommend up to 80 percent of someone's weekly training to be around a zone 2 intensity. The other 20 percent is reserved for harder efforts. This balance is called periodized training.

This, of course, depends on your fitness goals and on your current fitness level. If you're not in great shape or not regularly active, aim for 30 minutes three times a week of zone 2 training to start.

For fitter individuals, 45 minutes is the recommended minimum duration per session for zone 2 training. As fitness increases, you can build that time up to 90 minutes. Anywhere from three to four times per week is the suggested frequency, but you could do it more if you want — there's little downside to zone 2 training.

If you're new to zone 2 training, the big thing is not to get too bogged down by the specifics. "This is where we go totally off with the conversation," Magness says. "Of course the volume or the amount of work matters, but what the research shows and what we know from experience is just getting started and doing something will have some health benefits."

When it comes to zone 2 training, does it matter whether you choose to do it while swimming, biking, running or using the elliptical?

"It depends on your goals," Dr. Baggish says. "If your goal is health and general fitness then no, it doesn't matter at all. The body benefits from 'zone 2' in any modality."

But if your goal is something sport-specific — say, running a marathon — then yes, you'll want to focus on running. That gives you an opportunity to use zone 2 training time to help learn and improve your technique for that specific activity and goal, Dr. Baggish says.

• ‌Pick an enjoyable activity:‌ The best way to get started is to find something that makes you want to get moving. That could be walking your dog, going on a bike ride with a friend or going on a jog through your local park. Most often, people tend to exercise at harder intensities because they want to "get it over with." By selecting something you enjoy doing, you'll be more likely to keep the pace and effort in a zone 2 range.
• ‌Use the talk test:‌ "We have to learn to listen to our body a little bit, and the talk test is wonderful for that," Magness says. The talk test is just talking to a friend (or if you're alone, talking out loud to yourself) during your workout. You should be able to speak in full sentences without having to catch your breath. "Nine times out of 10, if you can do that, you're in a good easy pace or zone 2."
• ‌Bring your workout indoors:‌ Performing zone 2 training may be easier indoors. Why? You can control so many more variables — like temperature, humidity and elevation — during your workout.

You'll hear this term discussed a lot in the conversations around zone 2 training.

"Cardiac drift refers to the gradual uptick in heart rate that occurs during steady-state training," Dr. Baggish says. "This happens naturally as the body makes more adrenaline during prolonged exercise."

While it can't be fully avoided, adequate hydration can offset it dramatically, Dr. Baggish says. And ultimately, "it should not concern people as it is a natural response to sustained exercise."

If you notice your heart rate starting to rise toward the end of your workout, it's a great time to check other performance indicators. Try the talk test or listen to your breathing. Does your effort still feel as easy as when you started? If so, you can continue at that intensity, even if your heart rate shows you on the upper limits of (or outside completely) zone 2.

If your breathing is heavy, your legs feel especially tired or you're finding it hard to maintain a conversation speaking in full sentences, then you might want to consider slowing down your pace to help bring your heart rate down.

There's a lot of talk about zone 2 training today, and for good reason. It has a ton of health and performance perks, and there's not many people who ‌can't‌ benefit from doing more of it.

But don't feel like you won't get any benefit if you're not perfectly hitting zone 2.

"We use zones to categorize, but they're not perfect," Magness says. "The reality is that some days you're going to be on the bottom end of your zone 2, and that's great; some days you're going to 'go past' zone 3 for your easy workouts and that might be great, too."

Using zone 2 as a guide is great, but so is having a variety of intensities in your workouts.