Is Zone 2 Cardio Really the Best Kind of Cardio?

By Dr. Sean Hiller | PT, DPT, CSCS, BFR-L2, USAW-L1

If you've spent time on fitness social media recently, you've probably heard about Zone 2 training.

Zone 2 is everywhere. It has been promoted as the secret to improving cardiovascular health, increasing mitochondrial function, burning fat, and even supporting longevity.

And while there are legitimate benefits to training at a lower intensity, there is a problem with the way Zone 2 is sometimes presented:

It is not the only way, or necessarily the most efficient way, for the general population to improve cardiovascular fitness.

For many people, incorporating some higher-intensity training can provide a significant cardiovascular stimulus in much less time.

So should you abandon Zone 2? Absolutely not.

The better question is: What type of cardiovascular training gives you the most benefit for the time and effort you are willing to invest?

What Zone 2 Cardio Means

Heart-rate zones are simply a way of describing exercise intensity.

Zone 2 generally refers to relatively low-intensity aerobic exercise. You can sustain it for a long period of time, and you should be able to carry on a conversation while exercising.

Think:

- Brisk walking
- Easy cycling
- Easy jogging
- Hiking
- Light rowing

It is challenging enough to elevate your heart rate, but not so difficult that you feel like you are pushing your limits.

That is part of what makes Zone 2 so useful. It is relatively easy to recover from, which means you can do more of it without feeling wiped out.

Zone 2 Is Useful, But It Is Not Magic

There is nothing wrong with Zone 2 training. In fact, it is an excellent form of exercise. The problem is when we start treating it as though there is something uniquely magical about keeping your heart rate in one narrow range. Your cardiovascular system responds to exercise across a spectrum of intensities. You do not suddenly stop getting cardiovascular benefits because your heart rate goes above Zone 2.

In fact, as exercise intensity increases, the cardiovascular demand increases as well. That is where higher-intensity training becomes interesting.

Why Higher Intensities Matter

Zone 4 and Zone 5 represent much higher exercise intensities. At these intensities, you are working hard. You are breathing heavily. Holding a conversation becomes difficult or impossible, and you cannot maintain the effort indefinitely.

But that is also why these intensities can be so effective.

High-intensity exercise places a substantial demand on your cardiovascular system, giving your body a strong stimulus to adapt. For someone who only has 20 to 30 minutes available to exercise, that can be important.

Let's say you have an hour available for exercise. You could spend that hour walking at a comfortable pace, and that would be excellent.

But what if you only have 20 minutes?

You may be able to create a significant cardiovascular stimulus by incorporating periods of higher-intensity work.

This is one reason I do not want the general population to become obsessed with Zone 2 while ignoring higher-intensity training. The best exercise program is not necessarily the one that follows the latest fitness trend. It is the one that produces meaningful results within the constraints of your life.

Intensity Should Match the Individual

When we talk about Zone 4 or Zone 5 training, that does not mean you should walk into a gym tomorrow and sprint until you collapse.

Intensity should be appropriate for the individual. Someone who is completely sedentary needs a very different starting point than someone who has been training consistently for years. Higher-intensity work can be introduced gradually as your fitness improves.

For example:

Warm up → short hard interval → recovery → repeat → cool down.

The exact duration and intensity can be adjusted based on your fitness level, goals, and exercise modality.

For people with certain medical conditions or significant cardiovascular risk factors, it is appropriate to discuss exercise intensity with a healthcare professional before beginning vigorous exercise.

So, Does Zone 2 Still Have a Place?

Yes.

Zone 2 has a major advantage: you can do a lot of it.

You can walk for an hour without destroying your recovery. You can ride a bike while talking with a friend. You can hike on the weekend. You can accumulate aerobic activity throughout the week without making every workout feel like a battle.

That matters.

For the general population, simply becoming more physically active is one of the most important things you can do. Zone 2 is an easy way to accomplish that.

Instead of asking: "Should I do Zone 2 or Zone 5?"

Ask: "How can I use different intensities to build a well-rounded fitness program?"

Maybe you strength train three days per week. You could add walking or other lower-intensity aerobic activity throughout the week. Then you might incorporate one or two higher-intensity cardiovascular sessions, depending on your goals and ability to recover.

Now you are training multiple components of fitness instead of obsessing over a single heart-rate zone.

The Right Mix Depends on Your Goals

If you are training for a marathon, your program is going to look very different from someone who simply wants to improve general health.

If you are a competitive cyclist, you need a different program than someone who wants to walk without getting winded.

And if you are a 50-year-old who wants to stay active with your kids and grandchildren, you probably do not need to spend hours optimizing your mitochondrial function.

You need to be strong, mobile, and cardiovascularly fit enough to live the life you want.

That is a much more useful way to think about exercise.

The Bottom Line

Zone 2 training is valuable. But it is not magic, and it should not come at the expense of higher-intensity training.

For the general population, a combination of intensities is often more practical and effective than obsessing over one particular training zone.

Use lower-intensity exercise to accumulate activity, build aerobic fitness, and recover. Use appropriately prescribed higher-intensity work to challenge your cardiovascular system and improve your ability to perform at higher intensities.

And most importantly, do not let the pursuit of the "perfect" heart-rate zone keep you from doing something much more important:

Exercise consistently.

You do not need to optimize every workout. You need to build a body that can handle the demands of your life.

Move with purpose.

Sources:

• World Health Organization, *Guidelines on Physical Activity and Sedentary Behaviour*. Useful for supporting the recommendation that adults benefit from a combination of moderate- and vigorous-intensity aerobic activity, plus strength training.
   https://www.ncbi.nlm.nih.gov/books/NBK566046/
• U.S. Department of Health and Human Services, *Physical Activity Guidelines for Americans*. Useful for explaining moderate versus vigorous activity and how different intensities can count toward weekly activity goals.
   https://health.gov/sites/default/files/2019-09/Physical_Activity_Guidelines_2nd_edition.pdf
• Edwards et al., *Much Ado About Zone 2: A Narrative Review Assessing the Efficacy of Zone 2 Training for Improving Mitochondrial Capacity and Cardiorespiratory Fitness in the General Population*. Useful for a nuanced discussion of Zone 2 claims and the limits of treating Zone 2 as uniquely optimal.
   https://pubmed.ncbi.nlm.nih.gov/40560504/
• Wen et al., *Effects of Different Protocols of High Intensity Interval Training for VO2max Improvements in Adults: A Meta-Analysis of Randomised Controlled Trials*. Useful for supporting the idea that interval training can be an effective, time-efficient way to improve cardiorespiratory fitness.
   https://pubmed.ncbi.nlm.nih.gov/30733142/
• Weston et al., *Effectiveness of High-Intensity Interval Training and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials*. Useful for comparing interval training and traditional endurance training effects on aerobic fitness.
   https://pubmed.ncbi.nlm.nih.gov/26243014/

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