What is Zone 2 Training?
Zone two training is increasingly becoming more popular, but, the concept, methodology, and benefits have been well known in select circles for years. While it was initially the gold standard protocol for endurance training, Zone 2 training is becoming increasingly popular among health span enthusiasts for its lifestyle and longevity benefits.
Zone 2 training is a low-to-moderate level activity training threshold where I am in my highest fat-burning state. Zone 2 training strengthens my fat burning system, builds up my endocrine system and enhances my immune system.
It has also been shown to improve next-day recovery through measured increases in hear-rate variability and also supports better sleep and the increases my ability to oxidize fat – body fat as well as visceral fat – during other training efforts.
Technically, Zone 2 training is a training state equating to the maximum output I can perform while still exclusively utilizing my aerobic system, or without accumulating net lactate.
Practically, to be in zone 2 means I am training at a level where I can speak while performing exercise (generally biking, running, stairs, or rowing), but I am uncomfortable trying to hold a short conversation.
When I can no longer have a short conversation while training, I am likely past the Zone 2 threshold. To train in zone 2 means I am training at a pace and power output that is consistent and can be maintained for a substantial duration.
The distinction between zone 2 training and higher levels of activity primarily relate to the fuel source my body is utilizing for energy. Generally, the body uses two substrates for energy – either carbohydrates, in the form of glycogen, or fats, depending on whether I am above or below my aerobic, or zone 2, threshold. During zone 2, I am burning fat rather than glycogen for energy. However, as soon as I go above my zone 2 or aerobic threshold, my body switches the fuel source from fat to Glycogen, which is stored in muscle cells. BY training in zone 2, I am enhancing the ability and efficiency of my body to use fat as fuel.
To be in Zone 2, from a technical standpoint, means I am keeping lactate buildup in my body below a defined threshold; however, unless I was training for a marathon or ultra race, I don’t care to be too scientific on the lactate measurement as for me, it’s not necessarily practical to measure it that way. As a result, I leverage secondary metrics to manage my Zone 2 levels, which gets me close enough with a fraction of the effort or cost of measuring. By leveraging, first, my rate of perceived exertion (RPE), as well as my “breath test”, and second, both my theoretical and known max heart rate, I can triangulate when I am in Zone 2 and when I am falling outside the zone during training.
Why does Zone 2 Training Matter?
Zone 2 training provides the foundation for me to achieve my peak fitness and health span levels by efficiently creating energy, improving mitochondrial health, and burning fat.
Mitochondria produce energy in the body (ATP) through one of two fuels – fat or glycogen. During low intensity bouts of activity, such as during zone 2 training, mitochondria produce energy through the oxidation of fats. Fat stores are fueling your energy production when you are below the zone 2 threshold. When activity increases or intensifies, mitochondria switch their preferred fuel source from fat to carbohydrates, in the form of glycogen. Consistent zone 2 training improves metabolic flexibility – that is, the ability for my body to switch into the high-gear fuel source when needed, and to back down into reserves when appropriate during workouts.
This distinction in which fuel is utilized is critical to overall health and wellness. By training in zone 2, I increase my capacity to flip between burning fats and glycogen for energy, and in doing so, train my body to burn up fat stores both when I am at low to moderate levels of activity, as well as while I am at rest. Individuals who don’t have the ability to first burn fats and instead go right into burning glycogen, whether during activity, or even at rest, are prone to a condition called mitochondrial dysfunction which generally accompanies a host of age-related diseases including heart disease, type 2 diabetes, and cancer, to name a few. When mitochondria are functioning efficiently, energy production increases and performance increases – including physical performance, immune system performance, and cognitive performance.
If my focus is sports performance, the distinction between burning fats and glycogen is important as my body has a finite amount of glycogen it can store, and once I have exhausted my glycogen stores, I no longer have fuel sources available for high-intensity activity and I can no longer perform at a high level. If I have a low Zone 2 threshold, my body switches from burning fat to glycogen at lower levels of output, and I fatigue faster with lower output. Conversely, if I have a strong Zone 2 base, meaning I can generate more output at a lower level of exertion (defined as the zone 2 threshold), then my body is fueling itself from the near limitless fat stores longer, and I save the finite glycogen resources until I absolutely need them, resulting in the ability to perform at a higher level for longer.
Zone 2 aerobic training improves the overall health and efficiency of my mitochondria, as well as stimulates the creation of new mitochondria, a process referred to as mitochondrial biogenesis. Additionally, consistent zone 2 training has been shown to increase the number of mitochondria available to make energy, further increasing my total energy available. Further, during this process, old or damaged mitochondria are eliminated through a process called mitophagy, which is the body’s way of clearing out old, damaged, or dead mitochondria – much the same way autophagy is the body’s process for clearing out old, damaged cells. Thus, zone 2 training improves the overall health of my mitochondria, which is important because the healthier and more efficient mitochondria are, the greater my ability to burn fat which can aid in keeping visceral fat, or fat around internal organs, in check.
How do I Measure Zone 2?
Zone 2 can be measured in a variety of ways, some of which are more effective and/or practical than others.
The gold standard for measuring zone 2 is testing your lactate levels. Lactate is the byproduct of burning fuels in muscles, and the body clears lactate naturally. During exercise, I am naturally creating and clearing lactate. The key is whether I am net accumulating lactate – that is, am I producing more lactate (the “waste product”) than I am clearing? If so, then I am in a state of lactate accumulation. Generally, this threshold is approximately 2 millimoles per liter of blood, and this represents the Zone 2 threshold. If I am below two millimoles, I am clearing lactate at a rate equal to or greater than I am generating it, and as a result, I can continue training for hours. If I am above that threshold, lactate builds, glycogen is depleted, and fatigue sets in, eventually resulting in muscle failure.
Lactate accumulation is the true Zone 2 threshold. However, as I mentioned, unless you are serious about training for a marathon or ultra race, or, are already dialed in on 99% of the rest of your fitness, measuring your lactate is probably not worth your time and effort. Instead, I focus on two other metrics, my RPE and what I call the “breath test”.
My RPE when I am in zone 2 is between a 4 and a 6 out of 10 – where 10 is an all-out, max effort that I can endure for seconds. When I am in an RPE of 4 to 6, I feel like I could run, bike, row at the current pace for hours. I am breathing heavy, however, I can and only breathe through my nose, and while I could hold a short conversation with a friend at this level of exertion, I don’t want to as its uncomfortable to do so. When I get to a point where I no longer can breathe through my nose and feel I have to open my mouth to take in additional air, I have surpassed Zone 2 and I am now burning glycogen and accumulating lactate.
My heart rate is another tool that can be used to track my zone, but this is generally a poor approximation. But, if used in tandem with the RPE and breath test, can be a useful metric to baseline, and an even better one to gauge progress. If I was starting today, and I wanted to know what my zone 2 was in terms of heart rate, I would take my known max hear rate (the highest hear rate I have ever seen on my whoop) and take 75% to 85% of that rate. That is going to give me a decent approximation of my zone 2 ceiling and floor. The highest heart rate I’ve seen on my whoop is 185 beats per minute – which means my zone 2 range is approximately 135 to 155 beats per minute. Alternately, I could use my theoretical max heart rate, which is the 220 less my age equation, or 220-33 = 187, and take 70 to 80% of that number. Doing so gets me in roughly the same range as the first test, however, I would not rely on heart rate as it just not as good of a predictor of zone 2 relative to the RPE test.
How much Zone 2 Work is Enough?
A little bit of zone 2 training goes a long way.
Most people don’t do any zone 2 work – even those who classify themselves as runners. Most runners are running past zone 2, and walking is not active enough to get into zone 2. So, if my starting point is zero minutes of zone 2 work per week, any amount is going to be beneficial. Given my schedule, I target 120 minutes of zone 2 per week, and I split this up into 2-4 sessions of 30 to 60 minutes each. The optimal level is likely in the 180 minutes per week range, and while I know I am not in the optimal range, the 120 minute mark is what works for me and my schedule. While some weeks I exceed 120 minutes and some weeks I am short of it, I always get some zone 2 work in each week.
Zone 2 and the Impact on Weightlifting
Zone 2 training supplements my weight-lifting regimen.
I lift weights 4-5 times per week, and my primary goal for doing so, other than the fact that resistance training is one of the best things I can do for overall health and longevity, is hypertrophy. I use Zone 2 training as a supplement to my weightlifting regimen. Zone 2 has not been shown to block hypertrophy, but rather, Zone 2 training can provide benefits towards resistance training and weightlifting. Zone 2 training has been shown to improve the rate at which the body recovers during resistance training, resulting in the ability to lift more weight over time, as well as conditions the body to recover faster between sets. This leads to the ability to increase volume over time, which is the driver of hypertrophy. Additionally, if I am too sore to lift, a long bout of Zone 2 is a great way to get moving and work through soreness, enhancing recovery, and working through stiffness which can help prevent injuries, setting me up for the next training session. If my travel schedule takes me away from home and I don’t have access to a gym, a nice zone 2 run outdoors is a great way to see a new city, or simply get a good sweat in while traveling.
Other Benefits of Zone 2 Training
In addition to building an efficient energy source by burning fat, improving energy production and mitochondrial health, elevating baseline fitness levels, and aiding in hypertrophy and resistance training performance, Zone 2 training improves heart rate variability, lowers resting heart rate, and reduces risks of age-related diseases.
Consistent Zone 2 training has increased my heart rate variability (HRV), likely by the training of my body’s parasympathetic response to moderately intense exercise. By building my base, I am able to “do more with less”, that is, create more output by activating and consuming fewer resources, which is likely halting the engagement of my sympathetic nervous system, resulting in a higher HRV. Additionally, as is often seen, with a higher HRV, I see a lower resting heart rate (RHR) which means my heart is not working as hard to pump blood throughout my body – another sign of increased physical fitness.
Finally, as my metabolic health and metabolic efficiency improve, my risk of developing age-related diseases later in life, including cardiovascular disease, hypertension, and type 2 diabetes all decline.
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