Many beginners to running share a common belief: "To improve, I must push my limits in every workout; when the workout is over, I should be covered in sweat and completely exhausted." However, the biggest secret of endurance sports (running, cycling, swimming) is exactly the opposite: To become faster, you must spend most of your time running slowly. At the center of this rule, which sounds like a paradox, is "Zone 2" heart rate training. So what is Zone 2, why is it so important, and how can you find your ideal Zone 2 pace using our Running Pace Calculator tool?
What is Zone 2 (Heart Rate Zone 2)?
Our heart rate is generally divided into 5 different zones based on our effort level. While Zone 1 represents very light effort, Zone 5 means maximum effort (sprint).
Zone 2 is the effort level that corresponds to approximately 60% to 70-75% of your Maximum Heart Rate (MHR). The most distinguishing feature of this zone is that you produce energy entirely aerobically (using oxygen). Lactic acid does not build up while running at this pace, you can breathe comfortably, and theoretically, you can sustain this effort for hours.
How Do You Know You Are at a Zone 2 Pace?
If you don't have a heart rate monitor, the most classic way to tell if you're in Zone 2 is the "Talk Test." If you can chat with a friend next to you while running, forming full sentences without getting out of breath, you are at the right pace. If you are struggling to speak, having to break up sentences, or can only say "yes, no," you have probably moved into Zone 3 or higher; meaning you are too fast!
Why Should We Run Slowly? Benefits of Zone 2
Spending most of your time (80% of the training volume of all runners, including elite athletes) at this slow, conversational pace creates tremendous physiological changes in your body:
1. Mitochondrial Development
Mitochondria, the power plants of our cells, are stimulated to their maximum level and increase in number during Zone 2 training. An increase in the number of mitochondria means your cells can use more oxygen and produce more energy (ATP). This makes you more enduring.
2. Increased Fat Burning Capacity (Metabolic Flexibility)
At high heart rates (Zones 4-5), your body primarily uses carbohydrates (glycogen) for energy. Glycogen stores are limited, and when they run out, you "hit the wall." In Zone 2 training, the main energy source is fats. The slower you run, the more you teach your body to use fat as energy. This way, in long races like marathons, your body can endure much longer by burning fat without depleting carbohydrate stores.
3. Expansion of the Capillary Network
Long runs at a low heart rate expand the capillary network (capillarization) going to your muscles. This means more blood and oxygen are transported to your working muscles. As the oxygenation capacity of your muscles increases, you get less tired running at the same speed on race day.
4. Reduced Risk of Injury and Faster Recovery
Constantly running at a high pace puts a huge stress on your joints, tendons, and immune system. Zone 2 runs, on the other hand, strengthen your musculoskeletal system while causing much less wear and tear. The next day, you wake up with a fresh body, not with aches. This ensures training continuity.
How Do You Find Your Ideal Zone 2 Pace?
Zone 2 pace is often challenging for the egos of runners aiming to get faster. Many people unknowingly increase their pace and move into Zone 3, the "gray zone" (neither fully aerobic nor fully anaerobic), out of fear of "running too slowly, looking like I'm walking from the outside." This is the mistake that slows progress the most.
Your personal Zone 2 pace depends on your fitness level. For an average amateur runner, this pace is generally:
- 1.5 - 2 minutes slower than their target 5K race pace.
- 1 - 1.5 minutes slower than their target 10K race pace.
For example, if you can run your 5K race in 25 minutes (5:00 pace), your pace in Zone 2 training should most likely be in the 6:30 - 7:00 pace range.
To calculate your own values, you can follow these steps:
- Note the time of a distance you recently participated in or tested yourself on.
- Open our Running Pace Calculator tool.
- Enter the distance and time to find your "race" pace.
- Add 1.5 minutes to this race pace you found (especially if it's 5K or 10K) to create an estimated Zone 2 range for yourself.
The Place of Zone 2 in a Training Program (The 80/20 Rule)
The golden rule in the running world is the 80/20 rule. 80% of your total weekly kilometers (or time) should be spent at a low heart rate (Zone 2), and 20% at a high heart rate (Zones 4-5 interval and tempo runs).
If you are running 4 days a week:
- 3 of your days should be "very comfortable," conversational pace (Zone 2).
- 1 of your days should be challenging as an interval or tempo run (speed work).
In Summary
Leave your ego at the door. Don't mind if the pace on your watch looks slow. Your body needs that slow pace to build endurance at the cellular level. As you run patiently in Zone 2, you will find that within months you are able to run much faster (at a lower pace) at that same low heart rate. This is exactly how real acceleration begins.
