Let’s do Zone 2
Zone 2 Exercise and Metabolic Health
Zone 2 exercise has received growing attention for its potential benefits to metabolic health, and I’m a huge fan. Personally, it’s easier for me to commit to a Zone-2-ish brisk walk than a more vigorous workout like running. In Nature Wants Us to Be Fat, Dr. Richard J. Johnson (2022) recommends endurance-type exercise in Zone 2—about one hour, three or four times per week—to support mitochondrial health. The goal, as described in the book, is to keep exercise intensity around 70% of maximum heart rate, below the threshold where lactate begins to accumulate.
What Is Zone 2 Training?
Practically speaking, Zone 2 corresponds to roughly 60–70% of your maximum heart rate, often called a “conversational pace” (American College of Sports Medicine [ACSM], as cited in Elder, 2023; Cleveland Clinic, 2025). At this level, you should be able to maintain conversation but not sing.
There is some question, however, about whether this intensity is vigorous enough. Recent research indicates that while Zone 2 training is beneficial, it may not be uniquely optimal for mitochondrial or cardiorespiratory adaptations; higher-intensity intervals can sometimes yield greater benefits in less time (Storoschuk et al., 2025). Still, for many people, the accessibility and sustainability of Zone 2 activity make it a practical cornerstone of long-term metabolic health.
Physical Activity Guidelines for Americans
According to the Physical Activity Guidelines for Americans (U.S. Department of Health and Human Services [HHS], 2018), adults should engage in 150–300 minutes of moderate-intensity aerobic activity per week, or an equivalent combination of moderate and vigorous exercise, to achieve substantial health benefits and lower the risk of chronic disease.
Moderate-intensity activity is defined as 3.0–5.9 METs on an absolute scale or about a 5–6 on a 0–10 perceived-exertion scale. In practical terms, this is an effort level where a person can talk but not sing.
HHS also created the Move Your Way campaign to help Americans apply these guidelines in daily life.
The “Active Couch Potato” Problem
Even when people meet weekly exercise recommendations, too much sitting can diminish the benefits. The term “active couch potato” describes individuals who exercise regularly yet spend most of their day sedentary (Owen et al., 2010; Dunstan et al., 2012).
Prolonged sitting—eight or more hours daily—has been linked to impaired glucose regulation and lipid metabolism, independent of structured exercise. I relate to this personally: during years of doing vigorous HIIT workouts, I’d often spend hours afterward sitting at my desk.
To counter these effects, research suggests adding short movement breaks throughout the day—standing, stretching, or walking for a couple of minutes every 30–60 minutes—to improve metabolic flexibility and reduce sedentary time.
Balancing Strength and Aerobic Training
The key takeaway: we need to move, and likely more than most of us do. Regular movement supports health and helps prevent metabolic dysfunction, but it’s not just about weight loss.
A growing social media narrative claims that strength training is more important than aerobic exercise. In truth, both are essential. Strength training builds muscle mass and metabolic resilience, while aerobic exercise supports cardiovascular and mitochondrial health.
The best approach is to create realistic, individual activity goals that can be maintained over time.
Measuring Activity: Understanding METs
If you’re looking for ways to assess or diversify your physical activity, the Compendium of Physical Activities from Arizona State University’s Healthy Lifestyles Research Center is a valuable tool. It lists hundreds of activities with their corresponding MET values—from sleeping (0.9 METs) to intense running (18 METs).
MET stands for Metabolic Equivalent of Task and represents the energy cost of physical activity relative to resting.
1 MET = energy expenditure while sitting quietly, roughly equal to consuming 3.5 mL of oxygen per kilogram per minute, or about 1 kcal/kg/hour.
Examples:
Light activity: < 3 METs (slow walking, light chores)
Moderate activity: 3–5.9 METs (brisk walking, gardening)
Vigorous activity: ≥ 6 METs (running, fast cycling)
The Compendium allows users to browse activities by type—household, recreational, or occupational—and compare MET values to national guidelines for a more informed fitness strategy.
Final Thoughts
Zone 2 exercise offers an accessible, sustainable way to support metabolic and mitochondrial health, especially when combined with other forms of movement and reduced sedentary time. Ultimately, consistency matters most: find the balance of aerobic and strength activities that fits your life, and keep moving regularly for long-term wellness.
Disclaimer
This content is for general educational purposes and should not replace individualized medical or exercise advice. Always consult a qualified healthcare professional before starting a new fitness or training program.
References
Johnson, R. J. (2022). Nature wants us to be fat: The surprising science behind why we gain weight and how we can prevent—and reverse—it. BenBella Books. (See exercise recommendation: sustained ≥1 hour, 3–4×/week.)
Storoschuk, K. L., Moran-MacDonald, A., Gibala, M. J., & Gurd, B. J. (2025). 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. Sports Medicine, 55(7), 1611–1624. https://doi.org/10.1007/s40279-025-02261-y PubMed
Cleveland Clinic. (2025). Exercise heart rate zones explained (Zone 2 ≈ 60–70% HRmax). Cleveland Clinic
American College of Sports Medicine (via Elder, 2023). Moderate intensity ≈ 64–76% HRmax. Technologies, 11(3), 66.
U.S. Department of Health and Human Services. (2018). Physical Activity Guidelines for Americans (2nd ed.). U.S. Department of Health and Human Services. https://health.gov/paguidelines
Dunstan, D. W., Howard, B., Healy, G. N., & Owen, N. (2012). Too much sitting—a health hazard. Diabetes Research and Clinical Practice, 97(3), 368–376. https://doi.org/10.1016/j.diabres.2012.05.020
Owen, N., Healy, G. N., Matthews, C. E., & Dunstan, D. W. (2010). Too much sitting: The population-health science of sedentary behavior. Exercise and Sport Sciences Reviews, 38(3), 105–113. https://doi.org/10.1097/JES.0b013e3181e373a2
U.S. Department of Health and Human Services. (n.d.). Move Your Way. https://health.gov/MoveYourWay/
Ainsworth, B. E., Herrmann, S. D., Jacobs Jr., D. R., Whitt-Glover, M. C., Tudor-Locke, C., & Barreira, T. V. (2024). The Compendium of Physical Activities (Adult, Older Adult & Wheelchair versions). Arizona State University Healthy Lifestyles Research Center. https://pacompendium.com/
Ainsworth, B. E., Haskell, W. L., Herrmann, S. D., Meckes, N., Bassett, D. R., Tudor-Locke, C., ... & Leon, A. S. (2011). 2011 Compendium of Physical Activities: A second update of codes and MET values. Medicine & Science in Sports & Exercise, 43(8), 1575–1581. https://doi.org/10.1249/MSS.0b013e31821ece12
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