While there are many benefits of training by pace, it is also an equally valid approach to training—and sometimes even preferable—to always (or at least occasionally) ditch your pace and run by heart rate.
Heart rate training1Habibi, E., Dehghan, H., Moghiseh, M., & Hasanzadeh, A. (2014). Study of the relationship between the aerobic capacity (VO2 max) and the rating of perceived exertion based on the measurement of heart beat in the metal industries Esfahan. Journal of Education and Health Promotion, 3(55), 55. can help you truly tune in to how your body is feeling and slow down if need be without feeling pressure to hit a certain pace or distance.
The bulk of the training time for endurance athletes should be zone 2 cardio, despite the fact that we often want to run at a higher intensity.
In this guide to zone 2 heart rate training, we will briefly discuss how to train by heart rate and the five heart rate zones, what zone 2 cardio should feel like, and the benefits of zone 2 workouts for runners and endurance athletes.
What Is Considered Zone 2 Cardio?
Before we look at the benefits of zone 2 runs, let’s briefly review heart rate training and the target heart rate zones.
Heart rate zones are exercise intensity levels stratified by specific percentages of your maximum heart rate because your HR during exercise closely correlates to the percentage of VO2 max.2Cunha, F. A., Midgley, A. W., Monteiro, W. D., Campos, F. K., & Farinatti, P. T. V. (2011). The relationship between oxygen uptake reserve and heart rate reserve is affected by intensity and duration during aerobic exercise at constant work rate. Applied Physiology, Nutrition, and Metabolism, 36(6), 839–847. https://doi.org/10.1139/h11-100
The most common heart rate training model uses five heart rate zones. The five heart rate zones are as follows:
| Heart Rate Zone | Percentage of Maximum Heart Rate | Feels Like | Training Goals and Uses |
| Zone 1 | 50-60% | Very easy recovery, barely jogging, very low intensity exercise | Complete recovery, getting the body moving without stressing it |
| Zone 2 | 60-70% | Easy recovery jogging, conversational pace | Recovery runs, long runs, aerobic cross training, building endurance |
| Zone 3 | 70-80% | Moderate intensity sustainable for longer distance races (10k-marathon) | Tempo runs, race pace work for longer races |
| Zone 4 | 80-90% | Uncomfortable; around 84% of your max heart rate, you hit your ventilatory threshold, so your body starts relying on anaerobic metabolism to produce energy | High-intensity interval training, shorter races, VO2 max interval workouts, upper end of tempo runs |
| Zone 5 | 90-100% | All-out effort, usually only sustainable for 30-60 seconds | Sprinting, strides, hill repeats, plyometrics |
Zone 2 cardio workouts can be any modality of aerobic exercise that keeps your heart rate in the 60-70% of your maximal heart rate.
For example, Zone 2 running would be a lower intensity run at a pace where your heart rate is somewhere between 60-70% of your max heart rate.
How Do I Know If I’m In Zone 2?
Before you can do zone 2 training, you have to calculate your target heart rate for Zone 2.
Zone 2 is defined by a heart rate range of 60-70% of your max heart rate.
If you know your true maximum heart rate, you should use that for calculations; otherwise, you can estimate your age-predicted maximum heart rate using the following formula:
- Maximum Heart Rate for Males = 208.609-0.716 x age
- Maximum Heart Rate for Females = 209.273-0.804 x age
For example, if you’re a 36-year old male: 208.609-0.716 x 36 = 183 bpm.
If you’re a 36-year old female: 209.273-0.804 x 36 = 180 bpm.
Some people set up target heart rate zones using just maximum heart rate, but using heart rate reserve with the Karvonen formula is thought to be even more accurate for heart rate training, particularly for elite athletes and fit endurance athletes.
Your heart rate reserve (HRR) is your maximum heart rate minus your resting heart rate (HRR = Maximum heart rate — resting heart rate), so you can think about it as your “working heart rate range.”
For example, if your maximum heart rate is 180 bpm and your resting heart rate is 60 bpm, your heart rate reserve is 120 bpm.
Make sure to measure your resting heart rate first thing in the morning while you’re still lying in bed using a heart rate monitor, fitness wearable, or manually taking your pulse.
Then, you can use the Karvonen formula to calculate your zone 2 heart rate range as follows:
- Lower end of the heart rate range = 0.60 x HRR + resting heart rate
- Upper end of the heart rate range = 0.70 x HRR + resting heart rate
For example, with a max HR of 180 bpm and a HRR of 120 bpm:
- Lower end of the Zone 2 heart rate range = 0.60 x 120 + 60 = 132 bpm
- Upper end of the Zone 2 heart rate range = 0.70 x 120 + 60 = 144 bpm
This means the runner’s target heart rate for Zone 2 is 132-144 bpm.
What Are the Benefits of Zone 2 Training?
Here are some of the benefits of zone 2 cardio workouts for endurance athletes:
- Zone 2 cardio workouts build your aerobic base.3Pinckard, K., Baskin, K. K., & Stanford, K. I. (2019). Effects of Exercise to Improve Cardiovascular Health. Frontiers in Cardiovascular Medicine, 6(69). https://doi.org/10.3389/fcvm.2019.00069
- The cardiovascular adaptations of Zone 2 training include strengthening the heart muscle and increasing blood plasma volume, both which increase stroke volume.
When stroke volume is higher, the heart can pump more blood—and thus oxygen—to the muscles with every heartbeat. This can effectively reduce heart rate because the heart becomes more efficient.
- Additionally, there is an increase in capillary density, allowing for better delivery of oxygen and nutrients to working muscles, and an increase in mitochondrial density in skeletal muscles.
Mitochondria are specialized organelles, called the powerhouse of the cell, that produce ATP (energy) using aerobic metabolic pathways (in the presence of oxygen).
The more mitochondria the muscle fibers have, the better able the muscle fibers produce ATP through aerobic metabolism, helping increase your anaerobic threshold. This can help you run at a higher intensity or faster pace without fatigue.
- The cardiovascular adaptations and increase in mitochondria help increase VO2 max.4Filipas, L., Bonato, M., Gallo, G., & Codella, R. (2021). Effects of 16 weeks of pyramidal and polarized training intensity distributions in well‐trained endurance runners. Scandinavian Journal of Medicine & Science in Sports, 32(3). https://doi.org/10.1111/sms.14101
- Zone 2 training reduces the risk of overtraining syndrome by still providing a good cardiovascular workout to improve aerobic endurance while supporting the body’s ability to recover5Hwang, J., Moon, N.-R., Heine, O., & Yang, W.-H. (2022). The ability of energy recovery in professional soccer players is increased by individualized low-intensity exercise. PLOS ONE, 17(6), e0270484. https://doi.org/10.1371/journal.pone.0270484 by increasing blood flow and muscle repair.
Doing too much running at a moderate intensity (zone 3) is not easy enough to recover from high-intensity interval training (HIIT), speed work, sprinting, races, etc.
Because zone 2 workouts are lower intensity, you can recover faster6Hwang, J., Moon, N.-R., Heine, O., & Yang, W.-H. (2022). The ability of energy recovery in professional soccer players is increased by individualized low-intensity exercise. PLOS ONE, 17(6), e0270484. https://doi.org/10.1371/journal.pone.0270484 so you can do your next high intensity workout (in zone 4 or zone 5) with your energy levels recovered and good to go.
- Zone 2 running workouts help polarize your training, which can reduce the risk of injury from overuse that happens when you always run at the same moderate intensity pace.
- The Zone 2 heart rate is often called the “fat burning zone” because studies suggest7Carey, D. G. (2009). Quantifying Differences in the “Fat Burning” Zone and the Aerobic Zone: Implications For Training. Journal of Strength and ConditioningResearch, 23(7), 2090–2095. https://doi.org/10.1519/jsc.0b013e3181bac5c5 that maximum fat oxidation occurs around 70% of your max heart rate (and lower).
So, Zone 2 cardio workouts can help the body become more efficient at burning fat as an energy source rather than glucose (carbohydrates) as the only fuel source. This can be beneficial for preventing glycogen depletion for endurance athletes during long workouts and races.
How Much Should You Run In Zone 2?
Many endurance athletes, such as distance runners and cyclists, end up doing a lot of zone 3 running workouts, incorrectly thinking that this is still a good aerobic workout zone and that by pushing a little bit harder, they will experience cardiovascular and metabolic adaptations to training even faster.
However, heart rate zone 3 is often considered the “gray zone.“
This is because it isn’t easy enough to be considered an easy run pace or recovery pace, yet it’s not high intensity enough to derive some of the anaerobic improvements in VO2 max and running performance we hope for with interval training and speed workouts.
Rather, slowing down your easy run pace so that you are in zone 2 is a great way to reap the cardiovascular benefits of long runs and endurance workouts without taxing the body as much.
This allows for polarized training—running your easy runs at a truly low intensity and your hard workouts at a high intensity, which has been shown to be more effective for improving performance and reducing the risk of injury.8Kenneally, M., Casado, A., & Santos-Concejero, J. (2018). The Effect of Periodization and Training Intensity Distribution on Middle- and Long-Distance Running Performance: A Systematic Review. International Journal of Sports Physiology and Performance, 13(9), 1114–1121. https://doi.org/10.1123/ijspp.2017-0327
Most running coaches recommend you do at least 60-75% of your weekly running volume in zone 2 cardio.
Beginners especially should spend an even greater portion of their initial training at a lower intensity like Zone 2 aerobic exercise while the body begins to make cardiovascular adaptations.
Despite the fact that zone 2 runs usually feel super easy and slow, even elite athletes like Rich Roll spend most of their training time in the zone 2 intensity level!
For more heart rate training advice, check out this next guide:
