In this article we'll cover what zone 2 training is, why it's important, and how to do it.
What is zone 2 training?
The "zones" are the different heart rate zones that exercise physiologists use to describe exercise intensity. The scales vary a bit but typically go from 1 to 5. Zone 1 is an easy walk, whereas zone 5 is a maximal effort. Zone 2 is a level of intensity that is moderate and just below your aerobic threshold, generally where your muscles are using the greatest amount of fat as fuel rather than glucose.
Physiologically, the body's aerobic threshold is the point during exercise at which the body shifts from primarily relying on aerobic metabolism to anaerobic metabolism. It is the exercise intensity at which there is a significant increase in the production of lactate in the blood.
At lower exercise intensities below the aerobic threshold, the body can meet its energy demands primarily through aerobic metabolism. Oxygen is readily available, and the majority of energy production occurs through the breakdown of glucose and fatty acids in the presence of oxygen.
However, as exercise intensity increases and reaches the aerobic threshold, the body's demand for energy surpasses the oxygen supply available. This leads to an increased reliance on anaerobic metabolism, specifically anaerobic glycolysis, which produces lactate as a byproduct.
Why it's important
Training near your aerobic threshold can help improve aerobic capacity and endurance, as well as the body's ability to clear lactate more efficiently. It also helps determine optimal exercise intensity for individuals aiming to enhance fat burning during exercise. Since this is a low to moderate level of intensity, you are less likely to get injured and are less prone to chronic inflammation and burnout.
Perhaps more importantly, zone 2 training can help you live longer – a lot longer. Training in zone 2 trains your mitochondria (the parts of your cells that produce energy) to become more efficient at metabolizing fuel, especially fat. Burning fat as fuel is like burning an oak log. It burns cleanly and steadily for a long time. Burning glucose, which comes primarily from carbohydrates, is like burning newspaper. It burns hot and fast but can cause inflammation in the process. The human body is designed to burn both fuel sources, but metabolizing a greater percentage of fat is associated with improved health.
Zone 2 training can significantly reduce your risk of heart disease, neurodegenerative diseases (like Alzheimer's and Parkinson's), type 2 diabetes, and cancer. In fact, it's the single most powerful defense science has yet to find for these diseases of aging. By improving mitochondrial function, you literally slow down the aging process of your body at a cellular level. This is not some woo-woo claim or loose correlation. The science is robust.
How to train in zone 2
Zone 2 training can be done with various forms of activities that allow for a constant level of intensity, such as running, biking, rowing, swimming, or "cardio" equipment. Once you pick an activity you like, the next step is to determine your aerobic threshold heart rate. It's important that you use a chest strap to measure your heart rate for accuracy. I use a Garmin chest heart rate monitor that broadcasts to my Garmin watch.
You might see all kinds of formulas online about how to find your aerobic threshold based on some percentage of your maximum heart rate. In my experience, these are way off the mark. Here are a few different ways to subjectively gauge aerobic threshold without pricking your finger to measure blood lactate or measuring gas exchange.
Use Phil Maffetone's formula of [180 minus your age] to determine your aerobic threshold heart rate.
Talk test: You should be able to have a conversation at this intensity if necessary, but you probably wouldn't want to.
Nose breathe: You should be able to breathe through your nose but approaching your limit.
Feeling the burn: You should be at an intensity close to feeling the "burn" in your muscles, but you should NOT feel the burn from lactic acid building up.
I suggest doing these tests on a piece of equipment that you can keep your heart rate and pace steady, such as a stationary bike, treadmill, or elliptical. Once you determine your aerobic threshold, then you can train doing your activity of choice. Use the above 4 tests to hone in on your aerobic threshold. The best place to start is using the 180 minus your age formula pioneered by Phil Maffetone. So if you're 35 years old, try a heart rate of 180 – 35 = 145. Then use the other subjective tests to fine-tune. For me, 180 minus my age puts me exactly in the right zone. It's important to note that aerobic threshold will vary among individuals based on fitness levels, genetics, and training status. You might be a little frustrated at first that you're going too slow. That's normal. If you're accustomed to high-intensity, no pain no gain all the time, then this will feel slow. That's probably a good indication that your mitochondria and cardiovascular system need this type of training.
Once you determine your aerobic threshold heart rate, you'll want to stay at or just below it during your training. The beauty of zone 2 training is that it's pretty much impossible to overtrain at this intensity. More is usually better. A little is better than none. A good place to start is 3-4 sessions a week for at least 45 minutes.
You can measure your progress by doing the same route or activity every week or so. Stay in your zone 2 during your activity, and you'll see that over time, on average, you will get faster at the same heart rate and perceived level of effort. This is evidence that your mitochondrial function and fat-burning capacity are improving – clear indicators of health.
I've been doing this type of training with trail running for over 7 years, and I can say for sure that it works!
Here are some great resources if you'd like to learn more:
The book Natural Born Heros, it's one of the most influential books I've ever read!