Struggling with Zone 2 Running? You May Have Set Your Heart Rate Zones Incorrectly

The frustration is all too common: you know you should run a majority of your training easy, so you decide to start using a heart rate monitor. However, when you try to stay in zone 2 heart rate while running, you have to slow down so much you can barely shuffle. Does that mean you have “aerobic deficiency syndrome?” (No, it doesn’t.) Instead, research shows us that neither “zone 2” definitions nor predicted maximum heart rate formulas are one-size-fits-all. In this article, you’ll learn how to know if you set your zones incorrectly – and how to individualize your heart rate training zones.

(Importantly, heart rate training is not the superior method of training. Later in the article, I’ll describe other ways to gauge intensity on easy runs. For myself and my athletes, I do not rely on heart rate training, due to numerous confounding variables.)

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What the Newest Research Teaches Us about Heart Rate Zones

A recent 2025 study’s conclusions have significant impacts for how to use heart rate training – particularly, why zone 2 may feel too hard for some runners. This new study used a sample size of 50 endurance athletes – 30 male and 20 female. The athletes performed ramp and step tests in laboratory settings to assess lactate production, ventilatory rates, and substrate utilization. All three of these indicate metabolic thresholds (and therefore training intensities) with more precision than heart rate. Remember, heart rate is a proxy measure for these metrics.

The researchers found that standardized formulas, such as those that use heart rate max to set zone 2, are not accurate enough for training. The researchers noted that heart rate formulas had approximately a 5% interindividual variation. +/-5% may sound minor, but it actually can result in zone 2 being off by up to 10 bpm. 10 bpm is significant in practical training application, since that can mean an athlete’s training is off by a whole standardized zone. Ventilatory measurements provided accurate marker than standardized zone two predictions. (Meaning: the talk test may be more reliable than “70% of 220 minus your age.”)

What do these findings mean? Your zone 2 heart rate range may be different than another runner. For some, they can run at 80% of heart rate max and be in zone 2 – but maybe yours is at 69% HRmax.

Relying on inaccurate heart rate zones has training consequences. For some runners, these zones are too high, and they overreach in their training. For others, these zones are too low, and they do not reach their full training potential. Or, as I’ve observed, they become frustrated with easy running and give up on this valuable training practice altogether.

The diversity of zone two definitions reflects this study’s findings. Methodologies may delineate the zones differently, even when all use maximum heart rate as a reference point.

• The Norwegian Olympic Federation (and many research articles) define zone 2 as 72-82% of maximum heart rate.
• Dr. Stephen Seiler’s seminal 2006 study on training intensity zones found that low intensity running cut off at 81% heart rate max in trained runners (+/- 2).
• In a study of training qualities that predict performance, Casado et al. (2021) defined easy runs as “62 to 82% of HRmax,” with minimal mental strain.
• A 2024 study synthesizing 92 sub-elite marathon training plans defined zone 2 (”extensive endurance” as 73-80% of max heart rate.
• Jack Daniels’ Formula defines easy zone training as 65-79% of max heart rate.
• Polar defines it as 60-70% of maximum heart rate.

The Joe Friel method using lactate threshold heart rate defines zone 2 as 85-89% of lactate threshold heart rate. (Some though use <85% of LTHR to calculate easy zone heart rate, if they are functioning in a three-zone training paradigm.)

Other studies reflect the limitation of standardized heart rate formulas – this time, in regards to zone 2. A 2023 study with a sample size of 4043 runners (average age 33) looked at maximum heart rate formulas compared to cardiopulmonary exercise testing. Eight formulas overestimated HR by 4.9 beats per minute, while five formulas underestimated by 4.9 beats per minute. Another 2018 study of marathoners echoed these findings.

These minor discrepancies may seem insignificant, but precision matters for heart rate training. For example, let’s say your maximum heart rate is 188 bpm, but the standard formula estimates 184 bpm. Let’s then assume you use the most common zone two estimate from social media (70% MHR), but your actual zone 2 is at 79%. The standardized formulas predict your zone 2 ceiling as 129 bpm, while your actual zone 2 ceiling rests at 148 bpm.* No wonder you struggle with easy running!

Importantly, if a running coach is quick to prescribe your zone 2 heart rate range, without field testing your zones, be wary. A heart rate cap of 70% could undertrain you – or at least create undue frustration in training.

*Importantly, you don’t “go anaerobic,” get injured, or spontaneously combust when you exceed your zone 2 heart rate on a training run. You do shift from a higher ratio of fat oxidation to a higher ratio of carb oxidation, but you are still oxidizing substrate (using oxygen to produce substrate). Training intensities are a spectrum, not sharply delineated. You don’t want to do all training runs in zone 3, since it is more fatiguing. But you also aren’t undoing the whole session if you briefly spike up.

Field Tests for More Accurate Heart Rate Zones

Thankfully, you can use field tests to set your individual heart rate zones, if you want that training metric.

Max heart rate can be tested in a field test, although it’s not necessarily a pleasant experience. Using lactate threshold heart rate may be more reliable than using HRmax formulas, as this estimates the upper-end aerobic heart rate. (Lactate threshold heart rate will be at a varied percentage of maximum heart rate based on genetics, training, and other variables.)

To estimate lactate threshold heart rate (LTHR):

• Warm up with 10-20 minutes of easy running.
• Run 30 minutes as hard as you can while maintaining relatively even pacing. This should be solo-paced, on a flat and uninterrupted route. The test will start feeling as hard as a threshold run for the first 10-15 minutes, and become increasingly more difficult.
• Since heart rate takes time to elevate, you take the average heart rate over the final 20 minutes as your LTHR.
• Use <85% of LTHR as a safe estimate for easy zone heart rate.

To estimate maximum heart rate (from the Jack Daniels Running Formula):

• Warm up with 10-20 minutes of easy running.
• Run either 2 minutes all-out uphill, or 800m all-out on the track
• Check your heart rate at the end of each repeat
• Walk down the hill or for 2 minutes between the 800m
• Repeat 3-4 times (Your heart rate should be the same on the final 2 reps. If it keeps rising with each rep, repeat until you get the same reading for two consecutive reps.

Additionally, heart rate zones should be retested semi-regularly. Depending on your training status, your zone 2 heart rate may shift as you gain or lose fitness.

Whenever establishing heart rate zones, you want to be able to calibrate off of other physiological measures. This calibration allows you to learn how effort should feel based on internal variables and not just technology. Developing a sense of what is truly easy paces allows you to be less reliant on your heart rate monitor. Less reliance is valuable for when technology fails (your monitor’s battery dies, it doesn’t measure correctly for any reason one day, etc.) or in situations when heart rate isn’t as reliable (race day, interval workouts, etc.)

You can calibrate your zone two heart rate with these metrics:

• Talk test: Can you speak multiple full sentences without gasping for breath? Zone 2 running is a conversational pace (and natural conversation does involve pauses). You will have more labored breathing than at rest; however, speech should not be difficult.
  
• Observational test: How well can you take in your surroundings? Are you relaxed enough to observe people and animals? Your surroundings shouldn’t blur around you when you run at an easy pace.
  
• Fatigue assessment: You should feel minimally fatigued after an easy run (of less than 90 minutes; a long run may become more fatiguing even at an easy pace).
  
• Paces: A rough estimate is that easy pace is 1-2 minutes per mile slower than marathon pace (36-70sec/km) or 2-3 minutes per mile slower than 5K pace (70-110 sec/km) – although you can certainly go slower. Alternatively, you can estimate 65-85% of marathon pace or 50-70% of 5K. Don’t try to hit these paces, but rather use them as speed limits.

It’s important not to become so obsessive about zone two that you become anxious before each run. Not only does that remove the enjoyment of running, but stress and anxiety can literally elevate your heart rate. For many athletes, retrospective data and calibration are useful. Check your breathing rate during your run. Afterward, review your heart rate. If it stayed above zone 2 a majority of the run, make a conscious effort to slow down more next time.