Many runners assume you have to train fast to get faster, and while speedwork is an essential component of becoming a faster runner, it’s equally important to build your aerobic base with easy running.
That’s right—you actually have to run slow to run fast.
Heart rate zones denote different effort levels or exercise intensities, ranging from zone 1—very light effort—to zone 5, all-out, maximal intensity. Zone 2 training should be an integral component of any distance runner’s workout program.
In this guide, we’re going to look at:
- What Is Zone 2 Training?
- How Do You Calculate Your Zone 2 Heart Rate?
- Is Zone 2 Training Too Easy?
- What Are The Benefits of Zone 2 Training?
- How Much You Should Train In Zone 2?
Ready to train like an elite runner and smash your PRs? Keep reading for our complete guide to the science and benefits of zone 2 training.
What Is Zone 2 Training?
Zone 2 cardio, or zone 2 training, refers to performing workouts at an intensity level that lands your heart rate in zone 2. Heart rate zones are intensity levels stratified by specific percentages of maximum heart rate.
Because your heart rate increases with the effort or intensity level of a workout, and correlates with the percentage of your VO2 max, training by heart rate zones is a practical and feasible way to be precise and specific in quantifying effort level.
The five heart rate zones are as follows:
|Zone||Percentage of Maximum Heart Rate||Feels Like||Training Goals and Uses|
|Zone 1||50-60%||Very easy recovery, barely jogging||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%||Challenging, but doable, sustainable for longer distance races (10k-marathon)||Building aerobic fitness, getting a challenging aerobic workout|
|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||Tempo runs, interval training, shorter races, boosting performance|
|Zone 5||90-100%||All-out effort, usually only sustainable for 30-60 seconds||Increasing speed, strides, finishing kick, short intervals, hill repeats, plyometrics|
Zone 2 training involves running or cross-training at a pace that keeps your heart rate within 60-70% of your maximal heart rate. At first, this may feel painfully slow—almost impossible, at times, particularly if you hit a hill. However, over time, your body will adapt and you’ll be able to run faster paces while maintaining a zone 2 heart rate.
Even though it’s at the low end of the effort scale and can feel “too easy” to be beneficial to some runners, if you’re looking to run faster and improve your performance, you should actually be spending the bulk of your training time and mileage in your zone 2 heart rate.
In fact, if you look at the training logs of any elite or professional distance runner, you’ll find that the fastest runners are doing a significant percentage of their volume at paces that are slower than mid-pack finishers. This is because they are capitalizing on the benefits of zone 2 training.
How Do You Calculate Your Zone 2 Heart Rate?
Of course, you need to calculate your zone 2 heart rate in order to ensure you’re actually doing zone 2 training. Zone 2 is defined by a heart rate range of 60-70% of your maximum heart rate. If you know your maximum heart rate, you can use that; otherwise, you can estimate your 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.
Once you have your maximum heart rate, you need to calculate your heart rate reserve (HRR), which is your maximum heart rate minus your resting heart rate (HRR = Maximum heart rate — resting heart rate).
Measure your resting heart rate first thing in the morning while you’re still lying in bed. For example, if your maximum heart rate is 180 bpm and your resting heart rate is 60, your heart rate reserve is 120 bpm.
From there, you can determine your zone 2 heart rate with the following formula:
- 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
With an HRR of 120 bpm, for example, you would end up with the following:
- Lower end of the heart rate range = 0.60 x 120 + 60 = 132 bpm
- Upper end of the heart rate range = 0.70 x 120 + 60 = 144 bpm
This means the runner’s Zone 2 heart rate is 132-144 bpm.
Is Zone 2 Training Too Easy?
Competitive runners may worry that spending too much time training in zone 2 will make them slower, not faster, as the zone 2 heart rate is so low that running at that pace is typically much slower than their race pace.
However, research shows that the most successful approach to getting faster involves what is known as polarized training—running both very slow and very fast rather than just sticking at one constant pace day in and out.
In other words, it’s more effective to vary your intensity from workout to workout rather than mindlessly lace up the sneakers and plod along at the same pace every day. Some top endurance athletes like Rich Roll credit their peak performance and athletic success to zone 2 training.
What Are the Benefits of Zone 2 Training?
Besides being a good way to induce polarized training and change up the stimulus and stress placed on your body, Zone 2 training for runners is beneficial for the following reasons:
#1: Reduces the Risk of Musculoskeletal Injuries and Overtraining
Many runners fall into the trap of running almost every run at the same pace, landing somewhere in the moderately difficult intensity level. This can lead to overtraining and overuse injuries because the same stresses and intensities are placed on the body stride after stride, run after run.
In contrast, when a runner is constantly changing paces—running speedwork and slow runs—they introduce more stride variability and shift stresses on bones, muscles, and connective tissues. This can reduce the risk of injury and increase overall strength.
#2: Cardiovascular Benefits
Cardiovascular adaptations are among the top benefits of zone 2 training for runners. Because zone 2 training takes place squarely in the aerobic zone, zone 2 cardio strengthens the heart and lungs.
As the heart gets stronger, stroke volume increases, which means that the heart is able to pump more blood—and thus oxygen—out to the body every time it beats. This can effectively reduce heart rate because the heart becomes more efficient.
Capillary density increases, allowing for better perfusion of working muscles. Additionally, training in zone 2 stimulates an increase in blood plasma over time. This, in turn, also increases stroke volume, cardiac output, oxygen transport and delivery, and, ultimately, VO2 max.
#3: Metabolic Benefits
In addition to cardiovascular adaptations, zone 2 training induces metabolic benefits. Running at the same pace everyday limits improvement because the same physiological stresses are placed on the body with every run.
From a metabolic standpoint, the intensity level of a workout has a significant impact on the energy production pathways utilized.
Training too much at the same mid-range effort level, rather than capitalizing on the vastly different effort levels of polarized training, minimizes the potential training adaptations and metabolic improvements that can be gained by varying your paces and spending a lot of time running in zone 2.
Running in zone 2 increases the mitochondrial density in skeletal muscles, particularly in Type I muscle fibers. Mitochondria are cellular organelles, or structures, that produce ATP (energy) aerobically (in the presence of oxygen). The greater the mitochondrial density of your muscles, the more energy your muscles can produce to fuel your activity, delaying fatigue.
Zone 2 training relies on aerobic metabolism (Krebs cycle and electron transport chain) whereas speed work and effort levels in zones 4 and 5 utilize anaerobic energy pathways (glycolysis and the phosphocreatine (PC) system).
Again, by spending time training in zone 2 as well as zones 4 and 5 with polarized training, the body is forced to rely on different pathways of energy generation. This induces favorable adaptations in each pathway, making your body better equipped to handle the metabolic demands of running without your muscles accumulating painful, fatiguing acidic waste.
For this reason, polarized training involves your metabolic flexibility, meaning your body can easily produce energy through any of the metabolic pathways, and seamlessly flux between the reliance on different energy systems.
Finally, the metabolic adaptations of zone 2 training allow the body to become more efficient at using fat for energy rather than glycogen.
When your body gets better at meeting its energy needs by burning fat rather than stored carbohydrates, you delay potential “bonking” or “hitting the wall.” Seasoned marathoners may be aware of the dreaded onset of significant fatigue that may creep in around the 20-23 mile mark of a marathon, which is induced by depletion of the body’s glycogen stores.
Our bodies have a limited capacity to store carbohydrates in the form of glycogen, whereas even the leanest runners have enough body fat to fuel hours upon hours of exercise.
Zone 2 training causes favorable adaptations in fat metabolism, allowing you to run faster while still burning fat for fuel rather than carbohydrates. Ultimately, this can be hugely beneficial for marathoners as well as those looking to burn body fat.
#4: Recovery Benefits
Because zone 2 training is fundamentally quite easy, it allows your body to fully recover from hard workouts. This not only reduces the risk of injury but allows you to be ready to attack the next speed workout with more energy and intensity.
If you run a tough interval workout on the track on Monday, and head out for a moderately-intense zone 3 distance run Tuesday, your body will carry over more accumulated fatigue to a Wednesday tempo run than if you have taken your Tuesday recovery run as a true recovery workout in zone 2.
As a result, your performance on Wednesday’s effort may suffer and your risk of overtraining increases. In this way, training in zone 2 helps your body bounce back and recover after hard workouts.
How Much Time Should You Train In Zone 2?
The bulk of your training should actually take place in your zone 2 heart rate. Most top coaches recommend at least 60-75% of your weekly running volume should be zone 2 cardio, as this is the intensity level that forms your aerobic base. To reap the benefits of zone 2, long runs, recovery runs, and easy runs should all be run in zone 2.
For more information on heart rate training, check out our Heart Rate Training Zones Guide.