The Real Role of Zone 2 in a Smart Training Plan

I remember this ad campaign by Reebok called Run Easy.

It endorsed running at a talking pace and poked fun at athletes who nearly killed themselves in a mission to be their best.

Reebok followed up that 2007 crusade a few years later with the title sponsorship of the CrossFit Games—where finishing in a pool of your own body fluids became the hallmark of a great workout.

And again, my friends… how the pendulum swings.

The remarkable rise of Zone 2 training has taken over my news feed and is now all the rage.

I’ve seen a barrage of articles praising slower training as the key to going faster, while fitness influencers position it as a cornerstone of longevity.

So what’s actually going on here?

Background on the Zones

There are many variations of training zones—some use 5, 6, or even 7 zones.

But regardless of the system, Zone 2 consistently represents an easy aerobic effort that elevates breathing just enough to feel like a workout.

Key characteristics of Zone 2:

• Comfortable pace: You can hold a conversation without gasping for air
• Fat oxidation: A higher reliance on fat as a fuel source
• 60–70% of max heart rate: A common guideline (with plenty of individual variability)
• Lower stress: Easier to recover from compared to high-intensity efforts

If you want to dive into the complexity of the physiology of zone 2, then check out this podcast series with Iñigo San Millán, one of the leading researchers on the topic.

To boil down the science behind San Milláns zone 2 message, it's that for performance and health, we need strong and healthy mitochondria. 

The mitochondria are needed to create energy for sustained muscle contractions that work over a super long time by using primarily fat for fuel. Interestingly, mitochondria can also burn lactate as a fuel source.

With a robust system of mitochondria, our bodies become metabolically flexible to efficiently create a vast supply of energy for long, slow efforts, which then can also support the intense stuff by turning waste products into more fuel.

Notice the difference between elite athletes, weekend warriors, and metabolically sick people. 

(Source: San-Millán, I., & Brooks, G. A. (2018.) The elite endurance athletes have a massive capacity for burning fat as fuel, and they also maintain low lactate levels at high intensities—indicating huge aerobic engines powered by massive mitochondria.) 

The True Value of Zone 2

There is a message here worth spreading, but as a secret performance hack or the key to longevity, I find that zone 2 is largely overhyped.

For me, the value buried in the Zone 2 promotion is the realization that sustainable fitness isn't about constantly pushing ourselves to the brink but finding balance, longevity, and enjoying the journey.  

For example, I remember picking up road cycling in college, not to hone my mitochondrial density but to hang with friends. We would occasionally hammer it, but it was mostly coffee rides on open highways.   

Similarly, I've found that some of my best escapes aren't listed on my training plan. Easy runs with my wife, hikes with the dog, or exploring the outdoors add huge value to my life, but not because it checks the box as my zone 2 for the week.

My main message is for the go-getters who rolled their eyes as the 25-year-old me did at the run easy Reebok ad—sometimes movement provides gains more valuable than muscle growth or fitness.  

It's also a valuable note for those just starting. It's common to get inspired and jump head-first into a crush-your-soul fitness plan that quickly fizzles out.  

Instead, I like the message that there is some value even at manageable levels of exercise. If that's where you're at, go easy and enjoy the lifelong ride.

Zone 2 as a Training Tool

For those looking to maximize their fitness, some time in zone 2 helps build a well-rounded training program, but it's probably not the panacea we're making it out to be.

For starters, for the majority of people, efficiency is paramount. And if you're looking for the biggest bang for the buck, an hour on most days of interval training and strength work checks every box for one's fitness needs.

To highlight my point, if you do 4-5 hours per week of HIIT training, you could likely knock out a 90-minute zone 2 ruck without training. But simply rucking 4-5 hours per week would leave you ill-prepared for something like a CrossFit workout.

Then, for racing, the hype about slowing down to speed up doesn't do it for me either. First, you must test your lactate threshold in the lab to actually know your zone 2 pace.

But beyond that, I believe that the "sweet spot" for endurance exercise is the area just beyond Zone 2, which will push your physiology a bit harder, yet it is still sustainable.  

This chart shows what I mean,

(Source: Cycling Power Zones Explained by Andrew Coggan)

The Cherry on Top

For fitness enthusiasts and competitive endurance athletes, what we're truly getting at with zone 2 is the benefits of active recovery.

Getting out and sweating some is better than doing nothing to prepare your body for the next hard workout. And, your 5-mile trail run at 185 heart rate is not an "active recovery" day.

Overall, Zone 2 training has merits, but it's the cherry on top of the peak fitness plan, not the main course.