Zone 2 cardio: what it is, what it isn't, and how I actually use it.

If you follow health content online, you've probably heard about Zone 2 cardio. Peter Attia talks about it. Andrew Huberman talks about it. Instagram trainers talk about it. By the time most clients come to me asking about it, they've absorbed a lot of conflicting information and aren't sure what Zone 2 actually is or whether they should be doing it.

Here's my honest, grounded take. Zone 2 is genuinely valuable. It's also been slightly overcooked in the current wellness conversation. Both things can be true, and both things matter if you want to apply it well.

What Zone 2 actually is

Zone 2 refers to a specific intensity of aerobic exercise, roughly the intensity at which your body is primarily burning fat and lactate isn't meaningfully accumulating in your blood. In practical terms, it's the pace you can maintain while still being able to hold a conversation in full sentences, but where holding that conversation requires a little effort.

For most people, Zone 2 lives at about 60-70% of maximum heart rate, depending on individual physiology. More precisely, it's the intensity just below your first lactate threshold. If you have a lactate meter or can do a structured test, you can pin it down exactly. For most people, the conversation test is accurate enough.

Zone 2 training has been the foundation of endurance athletes' programs for decades. It builds mitochondrial density (the energy factories in your cells), improves metabolic flexibility (your body's ability to shift between burning fat and burning carbs), and increases capillary density (better oxygen delivery to tissue). These are real, measurable adaptations backed by decades of sports science research [1].

> Zone 2 is real training. It's the base of the pyramid, not the whole pyramid.

Why it's having a moment

The reason Zone 2 got popular in the mainstream wellness conversation is that it maps well onto healthspan research. Studies on mitochondrial function, metabolic flexibility, and longevity have shown that adults with better aerobic capacity in middle age have significantly better outcomes in old age [2]. Zone 2 training is one of the best tools we have for building that aerobic capacity without the recovery cost of harder intervals.

So when longevity-focused doctors and coaches started talking about it, they were pointing at something real. Aerobic base matters for healthspan, and Zone 2 is a reasonable tool to build it.

The issue is that the messaging got a little breathless. People started treating Zone 2 as a cure-all, spending hours a week on stationary bikes, stressing about whether they were in the exact right heart rate window, and ignoring other parts of their training because Zone 2 was supposed to be the main thing.

What Zone 2 isn't

Zone 2 isn't:

• A replacement for strength training. Aerobic base matters. So does muscle. Losing muscle mass in middle age is as consequential as losing aerobic capacity. The person who does only Zone 2 and no resistance training is missing the other half of the program.

• Necessarily the most efficient use of your cardio time. For certain goals (VO2 max, race performance), higher-intensity intervals are more efficient per unit of time. Zone 2 shines at building a long-term base. It doesn't build everything.

• A magic bullet. Mitochondrial density is one adaptation. Metabolic health involves sleep, nutrition, resistance training, stress management, and sunlight exposure, not just aerobic work.

• Only effective at a precise heart rate. People get anxious about being in "exactly" Zone 2 and check their watch every 30 seconds. The range is wider than the internet makes it sound. Being in the right ballpark is enough.

How I actually program Zone 2 for clients

For most clients, Zone 2 shows up in one of two ways depending on their background and goals.

Path 1: Walking. For the majority of my clients (busy professionals who want to be healthier and live longer, not race), the simplest way to get Zone 2 is brisk walking. Walking at a pace that makes you breathe a little harder but can still hold a conversation. 30-45 minutes, 3-5 times a week. Outside if possible. No heart rate monitor needed.

This might sound too simple to count. It does count. For someone with a sedentary job, walking 30-45 minutes a day at a brisk pace is meaningful Zone 2 work, and it's the version of Zone 2 most people can actually sustain.

Path 2: Bike, row, or run (for clients with goals or a base). For clients who are already training and want more structured aerobic work, I'll program 2 sessions of Zone 2 per week at 30-60 minutes each. Stationary bike, rower, or easy jog. Heart rate in the 60-70% of max range. Still able to hold a conversation.

Two sessions is plenty for most people. Four or five sessions is overkill unless you're training for an endurance event.

What to combine it with

Zone 2 is one lever. It works best inside a program that also includes:

• 2-3 strength sessions per week (non-negotiable, for all the reasons in my post on strength training after 35)
• One shorter, higher-intensity session per week (intervals or tempo work) for VO2 max adaptation
• Adequate protein to support recovery and muscle retention
• 7+ hours of sleep to allow the adaptations to happen

Zone 2 alone doesn't make someone healthy. Zone 2 as part of a complete program does.

The honest take

I'm not anti-Zone 2. I think it's a valuable part of a program. I also think the current wellness conversation has slightly oversold it, and a lot of busy professionals are getting the impression that if they just add Zone 2, they'll solve their health. They won't. They'll solve one piece, which is important, but they'll also still need the rest of the foundation.

If you're not currently doing any aerobic work, adding Zone 2 (even in the form of brisk walking) is one of the highest-ROI changes you can make. If you're already doing a lot of it and ignoring resistance training, you might be overweighting one variable at the expense of others.

The goal is a balanced program, not a single magic bullet. Zone 2 is one lever. Strength is another. Sleep is another. Nutrition is another. Pull all of them and your outcomes get better. Pull one and ignore the rest and you leave most of the gains on the table.

How to start this week

1. Add 3-4 brisk walks of 30 minutes each to your week. That's Zone 2 for most people, and it's the easiest entry point.

2. If you already walk a lot, add one structured session on a bike or rower. 30-40 minutes, heart rate in the 60-70% of max range.

3. Don't drop strength training to make room. Zone 2 is additive, not a replacement.

4. Don't stress about the exact heart rate window. Being in the right ballpark is fine. Perfection isn't the goal.

5. Track how you feel over 6-8 weeks. Morning energy, afternoon crash, workout recovery, mood. Zone 2's benefits compound slowly but reliably.

Zone 2 earned its moment. It's a real tool. Use it alongside the other real tools and you'll get the full picture of what your body can do.

Sources

• [1] Seiler, *What is best practice for training intensity and duration distribution in endurance athletes?*, International Journal of Sports Physiology and Performance, 2010.
• [2] Mandsager et al., *Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing*, JAMA Network Open, 2018.
• Peter Attia, *Outlive*, on Zone 2 training and metabolic health.