Finding Balance: The Underrated Value of Zone 2 Training

After decades practicing emergency medicine and now as an integrative physician, I've seen how exercise impacts long-term health. While high-intensity interval training (HIIT) dominates fitness headlines for aerobic activity, I want to encourage a new appreciation for something that might seem less exciting but is equally vital, if not more so: Zone 2 training.

What is Zone 2 Training?

Zone 2 refers to moderate-intensity exercise where you can still carry on a conversation. Technically, it's just below your first lactate threshold—around 60-70% of your maximum heart rate. At this intensity, your body will learn to increasingly burn fat for fuel while building cardiovascular endurance.

In practical terms? You're working hard enough to feel it, but not so hard that you're gasping for breath. You should be able to speak in short sentences while maintaining steady breathing.

The Cultural Bias Toward HIIT

Our society gravitates toward maximum results in minimum time. This cultural preference has fueled the explosion of HIIT workouts, which promise significant fitness gains in sessions as short as 4-20 minutes.

There's compelling research behind HIIT's effectiveness. Studies show short, intense workouts can improve VO₂max (a key measure of cardiovascular fitness) similar to longer, moderate sessions. In one landmark study, participants performing just 4 minutes of intense intervals saw comparable aerobic improvement to those doing an hour of steady cardio.

This efficiency appeals to our busy lifestyles. When "lack of time" is the most common barrier to exercise, it's no wonder we've embraced the "no pain, no gain" mentality. The fitness industry has capitalized on this with branded experiences like CrossFit, F45, and OrangeTheory.

But this preference for quick, intense workouts has overshadowed the unique benefits of slower, steadier exercise.

What Elite Athletes Know: The 80/20 Rule

Professional endurance athletes—cyclists, runners, swimmers—have long known something that recreational exercisers often miss: the power of Zone 2 training. Elite cyclists spend approximately 80% of their training time in Zone 2.

Why would professionals dedicate so much time to "easy" exercise? Because they understand it builds the cardiovascular foundation necessary for peak performance. They're going slower to eventually go faster, longer and more easily climb those hills.

This approach, sometimes called the "polarized training model," combines large volumes of low-intensity exercise (Zone 2) with strategic doses of high-intensity work. Research shows athletes following this 80/20 pattern often outperform those who focus mainly on moderate or high-intensity training.

The Science-Backed Benefits of Zone 2 Training

Zone 2 training offers numerous health benefits that complement and sometimes even parallel those of HIIT:

1. Mitochondrial Adaptation

Zone 2 training is often called "mitochondrial training" because it significantly increases the number and efficiency of your mitochondria—the cellular powerhouses that produce energy. At this intensity, your body maximizes fat oxidation while improving metabolic flexibility.

2. Cardiovascular Improvements

Regular Zone 2 training increases stroke volume (how much blood your heart pumps per beat) and improves capillary density in muscles. These adaptations enhance oxygen delivery throughout your body, improving endurance and exercise efficiency.

3. Metabolic Health

Studies show moderate-intensity exercise like Zone 2 training improves insulin sensitivity by about 20%—comparable to the improvements seen with HIIT. This makes it valuable for preventing and managing conditions like type 2 diabetes and metabolic syndrome.

4. Recovery and Sustainability

Unlike high-intensity exercise, Zone 2 training doesn't create significant muscle damage or stress hormone elevation. This means you can do it more frequently without overtraining, making it excellent for active recovery between harder sessions.

5. Longevity Benefits

High cardiorespiratory fitness strongly correlates with longevity and reduced disease risk. Zone 2 training builds this fitness foundation in a joint-friendly, sustainable manner that's accessible to people of various ages and fitness levels.

Finding the Right Balance: My Recommendations

Based on both research and clinical experience, here's how I suggest incorporating Zone 2 training into your routine:

For general health and longevity: Aim for at least 2-3 sessions of Zone 2 training per week, each lasting 45-60 minutes. This could be brisk walking, easy jogging, cycling, swimming, or using cardio machines at a (not easy) conversational pace.

For optimal results: Combine this with 1-2 weekly sessions of higher-intensity work (either HIIT or resistance training). This balanced approach provides the benefits of both exercise modalities while minimizing injury risk. As an alternative I tell my patients to do a steady 45 minutes of Zone 2 then add a 10-15 minute period of high intensity work through 30 sec to 1 minute repeats where you push hard for 30-60 seconds then ease off for 30-60 seconds repeating that pattern. That way they save 2-3 days a week for resistance work. 

For beginners: Start with more Zone 2 and gradually add intensity as your fitness improves. Zone 2 is especially valuable if you're new to exercise or returning after a break because it builds foundational fitness with lower injury risk.

For busy professionals: Even one or two weekly Zone 2 sessions can significantly benefit your health. Consider walking meetings, biking for transportation, or breaking up your day with movement breaks.

The Takeaway: Slow Down to Go Farther

Our cultural bias toward maximum efficiency has led many to view slower exercise as "wasted time." But the science tells a different story. Zone 2 training isn't less effective—it's complementary, providing unique benefits that high-intensity work alone can't deliver.

By rebalancing your exercise approach to include more Zone 2 training, you're investing in long-term health and performance. You're building the cardiovascular and metabolic foundation that supports everything else in your fitness journey.

So next time you exercise, consider slowing down. Find that conversational pace where you're working steadily but not straining. Your heart, muscles, and mitochondria will thank you—and you might be surprised at how this "slower" approach helps you go farther in the long run.

Notes

1. https://www.heart.org/en/healthy-living/fitness/fitness-basics/aha-recs-for-physical-activity-in-adults (www.heart.org)

2. https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2014.00033/full (Frontiers)

3. https://link.springer.com/article/10.1007/s40279-024-02120-2 (SpringerLink)

4. https://journals.humankinetics.com/view/journals/ijspp/aop/article-10.1123-ijspp.2024-0303/article-10.1123-ijspp.2024-0303.xml (Human Kinetics Journals)

5. https://www.youtube.com/watch?v=ptZCObCiQn8 (Dr. Iñigo San Millán interview on Zone 2) (YouTube)

6. https://pubmed.ncbi.nlm.nih.gov/8897392/ (Tabata et al., 1996) (PubMed)

7. https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0154075 (Gibala et al., 2016 sprint‑interval study) (PLOS)

8. https://pubmed.ncbi.nlm.nih.gov/32492705/ (Ryan et al., 2020 HIIT vs moderate training) (PubMed)

9. https://journals.lww.com/acsm-healthfitness/fulltext/2017/11000/worldwide_survey_of_fitness_trends_for_2018__the.6.aspx (ACSM fitness‑trend survey) (Lippincott Journals)

10. https://mcpress.mayoclinic.org/nutrition-fitness/zone-2-cardio-what-is-it-and-why-is-it-trending-online/ (mcpress.mayoclinic.org)