A while back, I read a very interesting article about heart rate zone training. (Thank you to my old YMCA director for sending it to me.) I found the article interesting because it took a deep dive into the benefits of training in different heart rate zones and how they’re linked to longevity. The unfortunate part of the article was that the author, Dr. Howard J. Luks, a leading Orthopedic Surgeon & Sports Medicine Specialist, jumped into the article as if everyone knew all about each of the 5 training zones.
Since the original article had so much great information, I’m going to fill in the gaps and start at the beginning. I want you to be able to reap all the benefits of understanding heart rate zone training, specifically the benefits of training in Zone 2.
What is Heart Rate Zone Training?
In the original article, Zone 2 Heart Rate Training for Longevity and Performance, it’s made very clear that training in different heart rate zones engages different aspects of our physiology. For this very reason, it’s important to vary your training intensity using heart rate as your guide.
If you wear some sort of heart rate monitor, it’s easy to track. If you have no monitor, use your first 2 fingers to check your pulse at your wrist (follow the line of your thumb down to find the spot) or at your carotid artery at the side of your neck and count the number of beats for either 30 seconds and multiply by 2 or count for a whole minute or 60 seconds.
The 5 Heart Rate Training Zones
As I mentioned, there are 5 training zones. Below, you’ll see how the zones are related to heart rates and the physiological effects that take place in each zone.
Zone 1 (Recovery/Easy) 55%–65% Heart Rate Max
Used to get your body moving with minimal stress and exertion. This zone might be used for an easy training day, warming up, or cooling down.
Zone 2 (Aerobic/Base) 65%–75% Heart Rate Max
Used for longer training sessions. You can sustain this basic-effort zone for many miles, yet still chit-chat a little bit with your workout partner.
Zone 3 (Tempo) 80%–85% Heart Rate Max
This is a zone where you push the pace to build up speed and strength; conversation is reduced to single words.
Zone 4 (Lactate Threshold) 85%–88% Heart Rate Max
In this zone, your body is processing its maximum amount of lactic acid as a fuel source. Above this level, lactic acid builds up too quickly to be processed and fatigues the muscles. Training in this zone helps your body develop efficiency when you’re operating at your maximum sustainable pace.
Zone 5 (Anaerobic) 90% Heart Rate Max & Above
This maximum speed zone (think closing kick in a race) trains the neuromuscular system—your body learns how to recruit additional muscle fibers and how to fire muscles more effectively.
How to Find Heart Rate Max
For reference, the physical activity guidelines state that adults should try to do at least 150 to 300 minutes a week of aerobic activity at moderate-intensity, which is 50%-70% of your Heart Rate (HR) max, so basically Zones 1 & 2. Or you should try to do 75 to 150 minutes a week of vigorous-intensity aerobic activity, which is 70%-85% of Heart Rate (HR) max, and will place you in Zones 2 & 3.
As you look through the zones, you see that everything is based on your Maximum Heart Rate (HR Max). Your HR Max is the absolute fastest rate your heart can beat. The rate is determined by your body, age, and fitness level. Note: your heart rate could be affected by medications you take, since some of them are designed to make sure your heart does not increase to its max.
The most accurate way to get your HR Max is to have a stress test. This is normally recommended and done by a cardiologist in a lab. Using this revised formula is a much simpler way to get your HR Max:
208 – 0.7 x your age
How Zone 2 Improves Longevity
Here’s where we get into the good stuff! Dr. Luks explains that the real benefit of heart rate zone training is what happens inside the muscle cells and the energy system that it uses, per the mitochondria. (Mitochondria produce ATP, the main energy molecule used by a cell.) Training in Zones 1 and 2 will actually improve mitochondrial number, function, flexibility, efficiency, and fitness. Thus improving aerobic health, or how easily you breathe while exercising.
Zone 2 training, also called low HR (heart rate) training or base training, can be used when cycling, swimming, rowing, running, or walking. Using this low HR zone training technique, according to Dr. Luks, is one of the best tools for achieving metabolic health and longevity.
This is significant because “most of the chronic diseases which will lead to our demise have a common root cause—poor metabolic health due to poor mitochondrial function.”
Poor metabolic health refers to the inflammatory process that happens in the body and leads to insulin resistance, type 2 diabetes, hypertension, dementia, cancer, allergies, coronary artery disease, arthritis, strokes, bowel, kidney disease, and more.
When it comes to mitochondria, the issues to be concerned with are: (as listed by Dr. Luks)
- The number of mitochondria you have. To increase the number of mitochondria, it’s recommended that 80% of your active training be done in Zone 2 or 1. It will take about 6 months to alter your mitochondrial physiology, so be patient. The tangible results will be more endurance, better resilience, stamina, and speed.
- The metabolic “flexibility” of your mitochondria. This refers to the ability of your mitochondria to utilize fat and glucose as an energy source. Exercising at a low heart rate means your main source of fuel should be fat and not glucose. If you have poorly functioning mitochondria, you’ll have an inability to utilize fat versus glucose. Unfortunately, this metabolic inflexibility is found in about 75% of people.
- Mitochondrial efficiency. When the body goes immediately to using glucose for energy, it produces excess lactate. The lactate can build up in the muscles if it can’t be used quickly enough for energy and cleared away. The problem with excess lactate is that it’s accompanied by a hydrogen ion. The hydrogen ion changes the pH in its local environment. When we’re exercising, that ends up being the skeletal muscle, and a change in the pH produces weakness and exhaustion.
“Zone 2 heart rate training enables you to use fat as an energy source for longer, and more efficiently. Thus, you preserve your glycogen stores for longer. Glycogen gets broken down into glucose, which serves as your fuel source for higher-intensity efforts. One end product of using glucose is lactate. Now, lactate isn’t as bad as you think it is. In trained individuals, they can shuttle the lactate back into the cell and use it as fuel! That requires an active transporter… MCT-1. The more Zone 2 exercise you perform, the more of that transport protein you will make. That improves your ability to clear the lactate. The mitochondria will take the lactate in and use it as fuel.”
To optimize your muscles’ mitochondrial function, it’s important to remember that there are 2 types of muscles. There are Type 1 or slow-twitch muscles and Type 2 or fast-twitch muscles. As you might suspect, the Type 1 fibers are rich in mitochondria and prefer fat as an energy source for fuel. The Type 2 fibers are glycolytic, which means they burn glucose and produce lactate.
When glucose is used for fuel, the lactate produced can overrun the system. The hydrogen ions will change the environment around the muscle cell and make it less powerful. Dr. Luks writes, “You can lose up to 50% of your muscle power as hydrogen builds up. That is the hallmark of fatigue.”
When you’re training, the goal is to fire all of your Type 1 fibers and not fire your Type 2 fibers. The recommendation is that you train these Type 1 muscles for a minimum of 45 minutes, staying in Zone 2 heart rate the whole time. If your heart rate increases at any time to Zone 3, it will change the physiology, and you will no longer be training your mitochondrial aerobic base. Even if you try to slow down after being in a higher zone, it will take a while to recover from the lactate buildup and return to fat oxidation.
To be clear, even in Zone 2, you will burn some glucose as fuel, and there will be a slight rise in lactate. But the levels should stay at a point where you can maintain your efforts.
According to Dr. Luks, the reason why you can maintain a low heart rate for a long time is that the body has an infinite source of energy available in terms of our fat stores.
Another way to gauge if you’re training at Zone 2 is to monitor your breathing. If you can breathe through your nose the whole time and you can’t “hear” yourself breathe, it’s more reflective of being in Zone 2. If you can talk easily in full sentences without having to pause, speak, or sing with an occasional pause to breathe, you’re probably in Zone 2 as well. If you can’t speak more than a few words without pausing, that probably means you’ve moved into Zone 3 or above.
Dr. Luks says that for many exercisers, staying at Zone 2 can be difficult. Especially if you’ve been used to exercising hard and leaving yourself breathless and fatigued. Going all out at the end of a workout is still acceptable, but to reap the benefits of Zone 2 training, it should be done only after spending at least 45 minutes totally in Zone 2.
Finding Your Heart Rate Reserve
The last important step in the article is how to find your heart rate range for your training. Dr. Luks calls it “heart rate reserve”. He finds the heart rate reserve by using a formula that includes the percentages in the chart of the 5 Zones, resting heart rate, and HR Max.
The best way to find your resting heart rate, if you don’t have a device, is to check it first thing in the morning before you get out of bed. Again, you can either count your pulse at your wrist or your carotid artery for 30 seconds and multiply by 2 or count for a full 60 seconds.
To find your heart rate reserve, plug your numbers into this formula:
% as 0.__ (HR Max — HR at rest) + HR at rest
Example: If I were calculating my heart rate reserve for Zone 2…
To find HR Max: 208 – 0.7 x 70 (age) = 159
My resting heart rate, according to my devices, is generally ~70 beats per minute (bpm)
To train in *Zone 2 at 65%-75% of HR Max I would calculate:
*0.65 (159 {HR Max} – 70 {HR at rest}) + 70 {HR at rest} = 128 bpm
*0.75 (159 {HR Max} – 70 {HR at rest}) + 70 {HR at rest} = 137 bpm
The other benefit of training in Zone 2 for 80% of the time is that it reduces the chances of overtraining. Overtraining can result in injuries or re-injuries, which are an all too common problem in older adults. I often remind my members, form is everything. But when muscles are fatigued–and now we know why that happens–it’s harder to keep good form, which can lead to an injury.
I learned so much more about heart rate training than I ever knew! I hope you did too.
The best part is, it appears that being a bit more deliberate in our workouts, by monitoring our heart rate more closely, can easily improve our metabolic health. In other words, without adding any extraordinary efforts, we can reap the benefits of boosting our mitochondria and their function to improve our longevity.
I know there is a lot of information here, so if you have any questions about this article, feel free to email me.
