Yes, Zone 2 Training Is Important. (Just Don’t Forget the Other Stuff.) 

Right now in the fitness community, the hottest topic is Zone 2 training.

Everywhere you look, both coaches and runners are extolling the benefits of running at a Zone 2 effort, while advising runners to be wary of running too hard on easy days.

Make no mistake: there are great reasons for running most of your mileage at an easy effort around Zone 2. No coach worth her salt will tell runners that easy running isn’t advantageous. In fact, a lot of easy running is the key to racing faster and building a strong body that’s resilient against injuries.

But with all this focus on Zone 2, are we ignoring other zones? What about Zone 1? Or what about Zone 3 (which seems to have become the boogeyman of running efforts)? Despite the baggage of Zone 3, and most athletes ignoring Zone 1, these zones still have value.

In fact, every zone has a place in a well-designed training program. Let’s get into the weeds, explore the nuance, and discover each shade of gray about zone training.

What is Zone 2 Running?

Zone 2 running is best defined as easy running where you’re still able to hold a conversation with a friend. The effort usually corresponds to about 60-70 percent of maximum heart rate.

This zone is part of the 5-zone system:

• Zone 1: very easy intensity that is considered “light exercise” with a heart rate of 50-60 percent of maximum
• Zone 2: easy intensity that is within about 60-70 percent of maximum heart rate
• Zone 3: moderate intensity that is within about 70-80 percent of maximum heart rate
• Zone 4: difficult intensity that usually corresponds to lactate threshold or 80-90 percent of maximum heart rate
• Zone 5: very difficult intensity that requires very hard exercise to reach 90-100 percent of maximum heart rate

Zone 2 is often considered the lowest intensity that produces meaningful training adaptations. It’s receiving a lot of attention in the running community because it has a lot of benefits with very little risk of over-training or injury. But this is not new. Runners have been married to the idea of easy running since the 1970s, when US marathoner Bill Rodgers was winning major marathons while running up to 180 miles per week—nearly all at an easy effort.

We’ve called long runs LSD (“Long Slow Distance”), short runs “recovery jogs,” and bemoaned our training partners for not running at “conversational pace.” In Boulder, Colorado, there’s a weekly “fun run” at such an easy effort it’s called “soft hour.”

Runners know and understand the value of easy, comfortable running. It’s just currently being rebranded into something new called “Zone 2 training” (just like, a decade ago, we heard all about High Intensity Interval Training—or hard track workouts).

Zone 2 is Just One Piece of the Puzzle

There’s no denying that Zone 2 is a key pillar of any endurance runner’s training—in fact, it’s likely the most important intensity zone for every runner—but that doesn’t mean it’s the only actor in the play. While it’s vital, it’s just one piece of the puzzle.

Zone 1 running can be enormously helpful for base building, especially with longer efforts that last multiple hours. A four-plus hour fast hike at altitude up a mountain is a good example of beneficial Zone 1 training.

However, Zone 1 isn’t as productive at producing endurance adaptations, so it’s usually reserved for cross-training, very long efforts, or just parts of certain runs (where most of the effort is Zone 2). A good example is a short recovery run where the first 10 minutes might be at a Zone 1 effort before gradually transitioning to a Zone 2 effort.

And while Zone 3 is often presented as a “danger zone” or the “gray zone” of training, it also has its place. High-level, competitive athletes have the talent to spend more time during an easy run at these moderate intensities. And beginners who are running low mileage can also do a fair amount of Zone 3 running because their volume is low, and they likely won’t make as many adaptations without it.

Just be careful with too much Zone 3 running: if more than 40-50 percent of your mileage is at this intensity, it presents a higher injury risk due to additional mechanical stress and less recovery due to higher intensities.

Of course, any performance-oriented runner with goals of running a certain finish time will want to spend time in both Zones 4 and 5, too, which we can consider “workout zones.” Race paces of 10K and faster fall into these zones and can be used for structured workouts for approximately 15-20 percent of total weekly volume.

An example week with mileage levels, workouts, and zones illustrates this concept:

• Monday: Rest Day
• Tuesday: 4 miles (Z1 and Z2)
• Wednesday: 7-mile workout (3 x mile at 5K pace/Z5)
• Thursday: 5 miles (Z2)
• Friday: Rest Day
• Saturday: 4 miles (Z1 and Z2)
• Sunday: 10 miles (with 3 miles at marathon pace/Z3)

In this example, the athlete is running 80 percent of their total weekly volume at a Zone 1 or Zone 2 effort, 10 percent of their effort in Zone 3, and 10 percent in Zone 5.

As we think about the complete training program over the course of a season, we can see that many intensities (like Zone 2) will remain constant throughout the season. Some intensities will have a stronger presence during the base phase, like Zone 1, while others will be prioritized late in the season (like Zone 5).

Just like a delicious soup, every ingredient has its place.

The Bottom Line

Clearly, I’m a Zone 2 stan. It’s an integral intensity zone for any runner, whether you’re a professional track and field athlete, frequent half marathoner, or a first-time ultramarathoner. If I was forced to choose the single-most important zone for running, I’d choose Zone 2.

But it’s not the only party in town. Every runner should strive to be a well-rounded athlete who’s capable at every intensity zone. Simply put: Zones 1-3 build capacity while Zones 4 and 5 sharpen your existing fitness. Any good training program should include a healthy mix of all zones because these energy systems all contribute to an athlete’s ability.

Ultimately, good runners have range at a variety of distances because they don’t ignore any zones or over-prioritize a specific zone. And that range—the ability to run well at the 5K, half-marathon, and ultra distances—is a testament to preparing every energy system during training.

Jason Fitzgerald is the host of the Strength Running Podcast and the founder of Strength Running. He writes The Performance Corner column for Trail Runner.