In Defense of Zone 3: The Most Misunderstood Training Zone

Recently Zone 2 training has become all the rage. Well, the term “Zone 2” is the rage. This type of training has been around for a long, long time. Arthur Lydiard was one of the key pioneers who presented the idea of jogging at a slower, more relaxed effort than race pace to develop your aerobic system. This concept has been one of the foundations of long-distance training for decades, but only recently has it been somewhat rebranded as “Zone 2.”

There are many different models for tracking training zones and paces, and you know what? I quite enjoy the five-zone model. It is fairly simple and easy to understand. I feel as though runners and coaches sometimes feel the need to overcomplicate things, getting too precise and nitpicky, when in reality most of us would be just fine following the classic adage: “Run often, run easy, sometimes hard.”

Having said all that, within the five-zone model I do feel that Zone 2 and Zone 4 get all the glory, while Zone 3 is a bit of the black sheep. It is often regarded as the “Grey Area” or as “Junk Mileage” — too fast for that nice, relaxed Zone 2 aerobic base-building pace, and too slow to reap the rewards of pushing your precious threshold in Zone 4 (or the sexiness of Zone 5 VO₂ max development). But I believe that when done with intention and purpose, Zone 3 can be quite beneficial. There is a why and a when for Zone 3 in run training.

Often described as tempo or “steady state,” Zone 3 can play an important role in developing a runner’s ability to sustain faster paces for longer periods of time. In terms of metrics, Zone 3 corresponds to approximately 70–80% of maximum heart rate, or about a 6–7/10 on the RPE scale. This is when conversational pace becomes difficult and you really need to start to focus. Zone 3 also typically aligns with marathon to half-marathon effort for most runners.

The why of Zone 3 training is its potential to support lactate management. Zone 3 intensity sits just below the anaerobic threshold, meaning the body learns to process and clear lactate more efficiently while still operating primarily through aerobic metabolism. This helps runners sustain faster speeds without accumulating fatigue as quickly.

Zone 3 also serves as a useful bridge between easy aerobic running and high-intensity interval work. It improves an athlete’s ability to maintain moderately hard efforts for long periods — which just so happens to be the demand of many road races such as the half marathon or marathon.

This brings us to the when of Zone 3 training. It is particularly valuable during the transition from a base phase to a race-specific build phase, when workouts begin to resemble the intensity and duration of competition.

A couple of my favourite Zone 3 sessions are a simple 30–45 minute steady-state effort within the zone. This offers great physiological benefit, and I also find it mentally beneficial as the athlete has to focus for a long duration without a break. Another added benefit of the long steady-state run is pacing practice. It will feel easy early on, but the effort will gradually grind on the athlete, providing useful information for longer races.

Another standard Zone 3 session is cruise tempos of 3–4 × 10–15 minutes with short 2–3 minute breaks between reps. I find these very useful early in a build when intensity and race-specific work are starting to pick up. Incorporating these sessions can also help runners develop durability and race-specific endurance without the excessive fatigue associated with harder interval training.

In summary, Zone 3 training is valuable because it enhances aerobic efficiency, improves lactate clearance, and builds the ability to hold long, steady efforts that closely replicate race-day intensity. When incorporated into a structured training program alongside a foundation of easy mileage and periodic high-intensity work, it becomes a powerful tool for improving race pace durability and overall endurance performance.

Rob Watson is a former professional runner and a current triathlete focused on the 70.3 distance. He is also the Head Coach of Mile2Marathon Vancouver: visit https://mile2marathon.com for more information.