Zone 3 Training + Avoiding The Grey Zone of Junk Miles

Plus, how to add zone 3 workouts to your training plan!


Perhaps one of the most counterintuitive things about running is that you often need to run slower to actually run faster and improve your performance.

Many endurance athletes end up in the “gray zone,” described as Zone 3 training, which can ultimately inhibit potential improvements.

Zone 3 running or training refers to running, or performing any type of exercise, between 70-80% of your maximum heart rate.

In this article, we will discuss Zone 3 running, if there is a grey zone in running, and whether Zone 3 training is junk miles a valuable part of your endurance training.

A person running on the coast.

What Is Zone 3 Training?

Zone 3 running refers to running, or performing any type of physical activity, in zone 3 of the heart rate training zone model.

In the traditional model of heart rate training, there are five intensity zones that correlate to different ranges of your relative maximum heart rate. Zone 1 is the lowest-intensity heart rate zone, and Zone 5 is the highest-intensity heart rate zone.

Here is a quick rundown of the five heart rate zones from low intensity to high intensity:

What Are The Heart Rate Zones?

ZonePercentage of Maximum Heart RateFeels LikeTraining Goals and Uses
Zone 150-60%Very easy recovery, barely joggingComplete recovery, getting the body moving without stressing it
Zone 260-70%Easy recovery jogging, conversational paceRecovery runs, long runs, aerobic cross training, building endurance 
Zone 370-80%Challenging, but doable, sustainable for longer distance races (10k-marathon)Tempo runs and race pace work for longer races
Zone 480-90%Uncomfortable; around 84% of your max heart rate, you hit your ventilatory threshold, so your body starts relying on anaerobic metabolism to produce energy Interval training, shorter races, boosting performance, the upper end of tempo runs
Zone 590-100%An all-out effort, usually only sustainable for 30-60 seconds Increasing speed, strides, finishing kick, short intervals, hill repeats, plyometrics

How Do I Determine My Zone 3 Heart rate For Effective Training?

To determine your heart rate zones, you multiply your maximum heart rate metric by the corresponding percentage of each heart rate zone. 

You can estimate your max heart rate with the Fox Formula: 220-age in years.

However, according to researchers, a more accurate estimation for max heart rate can be found through the following formulas:1Shargal, E., Kislev-Cohen, R., Zigel, L., Epstein, S., Pilz-Burstein, R., & Tenenbaum, G. (2015). Age-related maximal heart rate: examination and refinement of prediction equations. The Journal of Sports Medicine and Physical Fitness55(10), 1207–1218.

  • Maximum Heart Rate for Males = 208.609-0.716 x age 
  • Maximum Heart Rate for Females = 209.273-0.804 x age

Let’s take a look at an example of how to calculate your zone 3 heart rate zone.

Calculate Your Zone 3 Target Heart Rate Pecentages

42-year old female, intermidiate runner, using the Fox Formula:

1. 220-42 = 178 bpm Max Heart Rate
2. 178 x .7 = 124.6 bpm
3. 178 x .8 = 142.4 bpm
4. Zone 3 heart training range: 125-142 bpm

A person running trail.

What Are the Benefits of Zone 3 Training?

Zone 3 training is intended to develop your ability to run simultaneously farther and faster.

It is not meant to be a training zone for everyday distance runs or recovery workouts on easy days but rather specific targeted workouts like tempo runs and threshold intervals. 

Tempo runs and threshold training sessions span Zones 3 and 4, and these types of workouts have important training benefits. 

They condition the body to “get comfortable being uncomfortable“ for longer periods of time.

They also increase your lactate threshold, or the intensity level at which your body shifts from being able to produce nearly all of the necessary ATP (cellular energy) from aerobic metabolism (with oxygen) to anaerobic metabolism. 

The metabolic changeover that occurs at this physiological point is associated with a rapid increase in fatigue and a sensation of heavy, tired, burning legs.

Therefore, from a physiological standpoint, tempo runs improve your ability to produce energy aerobically, at higher intensities, and to clear acidic metabolic waste products as quickly as they are being produced so that you do not experience an appreciable decrease in pH, an acidic environment that causes a significant decrease in performance.

Although the lactate threshold can occur a bit higher (in Zone 4) for fit, conditioned runners, it often occurs in Zone 3 for beginners and less trained runners.

A person running in te suburbs.

According to research, typical lactate threshold values for different fitness levels are as follows:

  • Untrained or beginner runners: Corresponds to 60% of your VO2 max.
  • Intermediate runners: Corresponds to 65% to 80% of VO2 max.
  • Elite and highly competitive runners: Corresponds to 85% to 95% of VO2 max.

Therefore, because Zone 3 corresponds to a heart rate range of 70-80% of your maximum heart rate (which roughly correlates to the same percentage of your VO2 max), Zone 3 running for beginners and intermediate runners is right around the lactate threshold.

There are also mental benefits of adding Zone 3 workouts and goal race pace runs in heart rate zone 3 to your training plan.

Because the intensity level is somewhat uncomfortable, you are always flirting with the desire to ease up and slow down a bit. 

However, because many distance races, such as the half marathon and sometimes the 10k, are run predominantly in Zone 3, spending time with Zone three running workouts can help “harden“ your mental toughness to handle being uncomfortable for an extended amount of time.

Two people running in the suburbs.

Why Is Zone 3 Training Considered the Grey Zone of Running?

Zone 3 training becomes controversial because many runners spend too much time in this zone, particularly when they should be doing easier recovery runs in Zone 2.

This can either occur because the runner is not running with a heart rate monitor, so he or she isn’t aware that they are actually running faster and harder than they should be for an “easy“ run.

Or more often, many runners simply run their “easy runs“ and recovery runs too fast because they believe that running slowly will make them a slower runner and that pushing the pace will improve their performance.

For the first group of runners, wearing a heart rate monitor while running can be a very effective tool to help you be more informed and in control of your training.

For runners who do wear a fitness watch or heart rate monitor or generally just have the mindset that if they can run faster, they should run faster and that running faster will make them a faster runner, it could be helpful to understand why this is not true.

Teo people running on the beach.

Should You Train In Zone 3?

Not all Zone 3 training is considered running in the grey zone or “grey zone running.”

When you are deliberately running in Zone 3 by doing a tempo run or specific threshold or goal pace workout, any mileage that you do in Zone 3 is indeed highly valuable, effective training.

Where Zone 3 running becomes grey zone training, is when you are supposed to be doing a recovery run or easy run, and you are pushing the training intensity too high.

Easy runs should be run in Zone 2, not Zone 3.

When easy runs are run in heart rate Zone 3, your body is having to work too hard, and you are not actually facilitating any type of recovery.

In contrast, you are further stressing the body and digging yourself into a deeper hole regarding how much recovery will be needed to get yourself back to 100% for your next hard workout.

Two people running in the city.

The purpose of easy runs and recovery runs is to improve your aerobic capacity and fitness without overtaxing your cardiovascular, metabolic, and muscular systems.

Your body can make all of the necessary physiological adaptations for increased cardiovascular efficiency and improved aerobic endurance by running at a lower heart rate (those in heart rate Zone 2 rather than Zone 3).

Therefore, it is unnecessary to push the pace and bring your heart rate up in Zone 3 during these training runs, and more importantly, it is actually deleterious to your overall performance.

By running harder than you need to, your body isn’t getting the relative rest and recovery it needs, but rather continuing to be stressed and depleted. 

Over time, this can lead to overtraining syndrome because your body is never able to recover fully, and you keep stacking more training stress on the body. It is like trying to climb up an avalanche as it pommels down the mountain.

A person running next to a lake.

Additionally, on a more immediate time scale, Zone 3 training or running in the grey zone for your easy runs can compromise your performance in your key workouts during the week.

Imagine a scenario where you do a speed workout on the track on Tuesday.

If you are supposed to do a recovery run in Zone 2 on Wednesday before doing a tempo run on Thursday, but you do your recovery run in zone 3, your body will not fully recover by the time the tempo run rolls around. 

Then, when you try to run your tempo run, you will already be starting without a “full tank.“ This can reduce your ability to perform well in the workout and hit the proper paces at the appropriate corresponding heart rates.

Therefore, to avoid grey zone running or accumulate “junk miles,” let go of your ego, run your easy runs actually easy, and use Zone 3 for what it is intended to facilitate.  

To delve into more detail about tempo and threshold runs to add zone 3 workouts to your training program, check out our guides:

Tempo Runs

Threshold Run Guide

A runner zone 3 training.


  • 1
    Shargal, E., Kislev-Cohen, R., Zigel, L., Epstein, S., Pilz-Burstein, R., & Tenenbaum, G. (2015). Age-related maximal heart rate: examination and refinement of prediction equations. The Journal of Sports Medicine and Physical Fitness55(10), 1207–1218.
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Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a NASM-Certified Nutrition Coach and UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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