The Science Behind Zone 2 Exercise

A man bikes as a way to practice zone 2 exercise.

We all know “exercise is good for us.” But when it comes to what kind of exercise to prioritize, advice runs the gamut. (There are a lot of options!) Fortunately, we have science to guide us.

Exercise science research suggests that zone 2 exercise is one of the best forms of exercise you can do to maintain metabolic health throughout your life. Ultimately, zone 2 exercise is an essential — and we’d argue even foundational — component of a healthy, longevity-focused lifestyle. 

What Is Zone 2 Exercise?

Zone 2 is moderate-intensity exercise that can be maintained for quite a while — well over 30–60 minutes. That’s in part because, at this intensity, your body achieves peak fat burning, and even the healthiest among us won’t run out of fat reserves sooner than we’ll stop exercising.

To better understand zone 2 exercise, let’s put it on a spectrum: 

  • Zone 1: Very light intensity. Some people might call this “active recovery”; it encompasses any activity that is more rigorous than rest. Examples include leisurely walking, stretching, or yoga.
  • Zone 2: Sustainable, moderate-intensity exercise. This type of exercise maximizes your fat burning, which we’ll discuss more in a minute. Examples include power walking, jogging, or cycling.
  • Zone 3: Vigorous aerobic exercise. Here’s the level where effort level is high enough that you shouldn’t be able to maintain a conversation. When you’re in this zone, you should be able to keep up the effort for 30 minutes or less.
  • Zone 4: Intense anaerobic exercise. Now effort is ramped up even more. Your muscles are going to hurt, and you’ll start panting. You are unlikely to be able to sustain this exercise for longer than 10 minutes.
  • Zone 5: Top-end anaerobic/sprint exercise. In this zone, you’re at or near max capacity. You’re exerting yourself to such a degree that you might feel a little nauseous, like during a bout of HIIT or a 100-meter sprint. This exercise will only last 5 minutes at most.

Virtually all physical activity, regardless of zone, will benefit your health in some way. However, from a longevity standpoint, zone 2 provides specific benefits that are linked to the way your body produces energy during this type of exercise. 

The Zone 2 Energy System

Your body has a number of ways to produce the energy you need, whether you’re relaxing in a chair, doing hours of yard work, or sprinting to catch a bus. Generally speaking, there are two major energy production systems: aerobic (with oxygen) and anaerobic (without oxygen). The aerobic system requires active involvement of mitochondria — which, if you remember high school biology, are the “powerhouses of the cell” — to help turn the oxygen we breathe and the food we consume into energy. The anaerobic system, on the other hand, can produce energy without mitochondria. It does this when you’re exercising so intensely that slower aerobic energy production pathways can’t keep up with the demand for energy. The anaerobic system is also the one that produces lactic acid. 

Zone 2 exercise is unique because it’s precisely the intensity at which your cells achieve peak fat burning. At this intensity, you’re relying heavily on aerobic energy production, and you’re still able to clear lactic acid at the pace it’s being produced, so levels stay low (at 2mM or less). This means you can settle into a comfortable work rate while jogging, cycling, rowing, swimming, or even speed walking, since low lactic acid permits you to continue an activity for a long time without having to take rest breaks.

Building Your Own Zone 2 Exercise Habit

In order to see improvements in your health, build toward completing at least three zone 2 exercise sessions each week. Of course, we recognize that for many people, this goal is not the starting point.

Consider the following as you begin to build your zone 2 exercise habit:

  • If you exercise at all, you’re less likely to die. Science clearly shows that physical activity decreases mortality, regardless of demographics or age
  • While you’ll want to work your way up to 60-minute sessions, zone 2 exercise needs to last at least 20 minutes to stimulate fat burning. And the effort needs to be continuous, so try not to take breaks!
  • Mitochondria abide by the “use it or lose it” axiom, so if they’re not getting a signal frequently enough, they won’t gain the fitness they need to be ready for your next exercise session. That’s why the goal is to get at least three sessions of zone 2 exercise per week — you want to keep those mitochondria working. If you can build all the way up to five to seven sessions each week, that’s even better.
  • If you like to use heart rate to judge your effort, your heart rate during zone 2 exercise will typically fall between 60% to 80% of your maximum heart rate (HRmax) — toward the lower end of that range if you’re just beginning to build your exercise habit, and toward the higher end if you’ve been exercising for some time.

As you build your zone 2 exercise habit, you’ll likely feel and even see the physical benefits. However, tangible results can take time. To stay motivated in those early days, know this: A regular zone 2 exercise habit is also shown to help prevent chronic disease. According to CDC data gathered from over 86,000 participants between 18-64 years old, 70% of those who completed at least 150 minutes of moderate physical activity per week (fewer than four 45-minute sessions!) have zero chronic disease. How’s that for motivation to move?

References

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Buowari, D. Y., & Kanmodi, K. K. (2022). Exercise, Health, Longevity and Social Media: A Discourse. In Healthy Lifestyle(pp. 143-155). Springer, Cham.

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Myers J, Kokkinos P, Arena R, LaMonte MJ. The impact of moving more, physical activity, and cardiorespiratory fitness: Why we should strive to measure and improve fitness. Prog Cardiovasc Dis. 2021 Jan-Feb;64:77-82. doi: 10.1016/j.pcad.2020.11.003. Epub 2020 Nov 5..

Carroll DD, Courtney-Long EA, Stevens AC, Sloan ML, Lullo C, Visser SN, Fox MH, Armour BS, Campbell VA, Brown DR, Dorn JM; Centers for Disease Control and Prevention (CDC). Vital signs: disability and physical activity–United States, 2009-2012. MMWR Morb Mortal Wkly Rep. 2014 May 9;63(18):407-13.

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