Surprising Benefits of Low Intensity Exercise - Lactate Zone 2

In this article, we will lay out why incorporating long, slow, and easy workouts has massive benefits to high-intensity performance, we’ll lay out the MovementLink Protocol for this specific Lactate Zone 2 training, and we’ll link to some of our favorite experts below.

What if, when we pushed hard, we did not feel the “muscle burn” as much? There is myth that roams around the high-intensity, functional fitness world that aerobic training (longer, slower efforts) is muscle wasting and has very little to no carry-over to anaerobic training (shorter, heavier, harder efforts). The high-intensity world (and so did we for that matter) wanted our wide variety of high-effort workouts to be the optimal solution to developing all around fitness, but we now know this is a myth and that the reality is that only training in these higher intensity ranges leaves a major gap in one’s athletic and health potential - a gap that can only be filled with also training at low intensity. Now, before the high-intensity only people get too upset, we do strongly believe that if we had to choose a high-intensity only program or a long, slow, low-intensity only program, the high intensity program would be vastly superior to a low-intensity workout program in almost every way. But, that is not how the world works and we do not have to choose one polarized approach or the other. Although we are going to talk about Lactate Zone 2 training in this article, the endurance community has been close to this for years with their incorporating of heart rate zone 2 training - there are 5 heart rate zones and 2 is a very low intensity zone. They have understood how effective this type of training is for their endurance events, but the high-intensity community has been reluctant to slow down. With the new science that has come out around our mitochondria’s ability to recycle lactate and therefore reducing blood lactate levels, high-intensity athletes’ ears everywhere should perk up because lactate build-up in the blood is a major thing that hold people back from pushing harder. We are also now understanding that the ability of our mitochondria to recycle lactate is only significantly improved through Lactate Zone 2 training, which tends to correlate reasonably well with heart rate zone 2 training. The benefits of this are astronomical for high-intensity athletes. Although our minds have been blown, it seems the best athletes in the world have be onto the benefits of low-intensity training for a very long time, even the sprinters - Let’s dive in!

Michael Phelps is arguable the best Olympic swimmer to ever live. His events range from about 20 seconds to about 4 minutes long. As a sprinter, why then would Phelps have spent the majority of his training time doing long, slow swimming - Especially if long, slow training is muscle wasting and had no carry-over to his sprint events?

To oversimplify how our body produces and uses energy:

Our body loves to use Adenosine Triphosphate (ATP) for energy, but it needs to make it.
There are three major metabolic pathways that our body utilizes to create energy (ATP) for us to use:
- Oxidative system uses fat and lactate as fuel. These are extremely abundant resources, but it takes a bit of time to produce ATP. This system is the primary source when we are at rest and for multi-hour plus efforts.
- Glycolytic system uses glycogen (from tissues) and glucose (from blood, think carbohydrates and sugar) as fuel. This is readily available, but stores are limited. This our bodies go-to for short to medium efforts (like 1min to 1hr), especially high-intensity workouts.
- Phosphagen system uses stores in our muscle cells. This is the quickest available, but also runs out very quickly and is our bodies go-to for very, very short efforts (~8-10 seconds).
- It is important to note that our body is will derive energy from all three of these systems at almost all times, just at different levels. So in a hard 10 minute effort, all three metabolic pathways will be utilized, but the primary source of fuel will likely be glucose.
Lactate is a biproduct of exercise, especially high-intensity or anaerobic exercise. Through high-intensity training, athletes build the ability to create more and more lactate and to better handle higher blood lactate levels.
For the Oxidative system, Mitochondria use oxygen, fat, and lactate to produce energy (ATP). So, our body feeds mitochondria oxygen, fat, and lactate, and they pump out ATP for us to use. We then use that ATP as energy which produces lactate, some of which gets recycled back to the mitochondria who, in turn, gobble it up and spit back out more ATP! It’s a symbiotic recycling system that is win-win!

Previously, it was believed that mitochondria only used oxygen and fat to create ATP, but it’s this new mechanism - The ability of our mitochondria to recycle lactate into ATP that we then use for more energy - that makes the role of mitochondria in high-intensity performance, so key. If a high-intensity athlete develops the ability to recycle more and more lactate, there is a 2-hit benefit: 1) they not only reduce their blood lactate levels, but 2) they have more energy to use from this recycling. So what they heck are mitochondria?

Our Relationship with Our Mitochondria: The Big Picture

We have trillions of mitochondria in our body that live within our cells. Mitochondria are fascinating because although they live inside of us, they are their own single-celled organisms, with their own DNA, that communicate and work symbiotically with us at the cellular level. Part of what makes us age is the breakdown of communication between our mitochondria within our cells and the nucleus of our cells which hold our DNA and epigenome (the reader of our DNA). The healthier and more abundant our mitochondria, the healthier we are. The molecule Adenosine Triphosphate (ATP) has become the choice energy molecule for us humans. Millions and millions of years ago, multi-celled organisms who wanted to use the energy rich ATP as fuel found a way to absorb mitochondria into themselves and developed the ability to feed the mitochondria oxygen and then use the mitochondria’s’ ATP biproduct as their own energy source. Millions and millions of years later than that, we have evolved a similar relationship with them. Currently, our mitochondria use oxygen, fat, and lactate to produce their own energy which creates the bi-product ATP that we use for energy. Another thing we find fascinating is that our genes are a combination of our mother’s and father’s DNA and epigenomes, but our mitochondria and their DNA come straight from our mother. Mitochondria live inside of our cells, but they are not us. So, because we are created inside our mother’s wombs, our cells have a nucleus made up of our mother’s and our father’s DNA and epigenome (DNA reader), but the mitochondria in the cells come straight from our mother.

This symbiotic relationship between us and our mitochondria is the focus of our low intensity training. Through lactate zone 2 training, we are not just working out ourselves, we are working out in a way that provides an effective workout for our mitochondria.

Lactate Zone 2 Training targets a specific level of muscular effort in which the oxidative pathway is our primary source of creating energy. If we push too hard, we start using more glucose as our primary fuel source and our reliance on our mitochondria's ability to turn oxygen, fat, and lactate into fuel (ATP) decreases. By training specifically in this lactate zone 2 level, we are requiring our mitochondria to be highly involved as our primary fuel source. Through this, if we hold our effort right in this goldilocks zone for our mitochondria, they effectively are getting their own workout and over time they multiply in number and our cells get better and better at converting oxygen, fat, and lactate into ATP for us to use.

2-Hit Benefits of Mitochondria Getting Better at Recycling Lactate

Mitochondria pull lactate from our blood, reducing our blood lactate levels, as they use it for their own energy.
The biproduct of mitochondria burning lactate for their energy is ATP. We can use that ATP for more energy.

This symbiotic lactate recycling system is a huge win-win for our fitness. Such a huge win-win, that we believe one cannot be world class without building this ability to efficiently recycle lactate into ATP. If we train exclusively with relatively high-intensity efforts, we get really good at

producing high amounts of lactate,
we build a ton of MCT-4 transporters to transport that lactate out of our muscle cells, and
we gain the ability to handle high lactate levels.

These are all amazing things and all things that high-intensity exercise is great for. High-intensity exercise also will increase MCT-1 transporters, which take the lactate out of our blood stream and into our cells for our mitochondria. But, although MCT-1 transporters rise quickly when high-intensity exercise is first introduced to us, they cap out quickly and at a level that is dramatically below a level that can be achieved through Lactate Zone 2 training. Because of this, high-intensity only athletes tend to have relatively poor mitochondria function. Without adequate time spent training our mitochondria, we are left with creating and dealing with a ton lactate. By adding in the right amounts of low-intensity training with our high-intensity training,

we can develop the ability to produce high amounts of lactate,
we build a ton of MCT-4 transporters to transport that lactate out of our muscle cells,
we develop to handle high amounts of lactate,
we build a ton of MCT-1 transporter to transport the lactate out of our blood for our mitochondria’s use, AND
build a team of mitochondria that can recycle high amounts of lactate out of our blood and turn it into more ATP.

A combination of high-intensity and low-intensity training work together to provide amazing benefits.

So, what are the MovementLink Lactate Zone 2 Training Protocols?

First of all, when we talk about Lactate Zone 2 training here we want to be clear here again that we are not exactly talking about Heart Rate Zone 2. Depending on the exercise(s) we choose, our heart rates will likely vary significantly at a lactate zone 2 level. But, within a single modality, like running, we can use heart rate over time as a metric to help our paces that will put us in lactate zone 2. So, although heart rate can be a reasonable metric to use as an indicator over time with specific exercises, there doesn’t seem to be a specific heart rate zone (or power output, etc.) that will ensure your are in a lactate zone 2 across all exercises. Power tends to be another useful indicator, but can be tough to get accurate readings, especially when running, rucking, etc. outside. Additionally, heart rate and power output are variable day-to-day based on a number of recovery factors, so we find it’s best to use both of these metrics when available and to also go by feel. We prefer a Relative Perceived Exertion (RPE) rating where you simply learn how your body feels at different lactate levels. We do find it beneficial to pay attention to heart rate and power zones as you develop your ability to estimate your RPE as it takes experience to get a good feel for. An RPE of 10 is a max effort and an RPE of 0 is no effort. High intensity exercise will typically fall with RPE ratings of 7-10, and the Zone 2 training we are discussing here will come with an RPE of 4-5, which to people who are accustomed to high-intensity exercise, will feel very slow. For Lactate Zone 2 training, heart rate will typically fall between 50%-75%, but, again, this is will highly dependent on the exercise.

Why not just measure lactate levels? Well, it’d be great, but it’s expensive and, as far as we know, requires blood from a finger prick on a measuring stick and then only gives a snap shot of our lactate level at that exact moment, so not exactly real-time information. Our assumption is that at some point in time, just like there are wearable blood glucose monitors, there will be wearable blood lactate monitors, but as far as we know (when we wrote this), they do not exist. With the best in the world getting by with heart rate zones, power meters, and RPE, that' is our current preferred method of finding paces that put us in Lactate Zone 2.

If we aren’t talking about heart rate zones, then what are the lactate zones?

Lactate Zone 1: Resting or very easy effort in which you could basically go all-day. This is the top zone to be in if your goal is recovery as it is not really fatiguing, but promotes blood and lymphatic flow. Here, fat oxidation is the primary energy source, but we still use some glucose.

Lactate Zone 2: Exercise with lactate blood levels below 2 mmol/L. We can hold a conversation, but the other person would know we’re exercising. Our RPE is around 4-5, an effort level that feels like we could sustain it for hours and hours. Here we’ll use more fat and more glucose, but our primary source of energy comes from our mitochondria via fat oxidation and lactate. As we push to the border between zone 2 and zone 3, our mitochondria are stretched to their limits.

Lactate Zone 3: As intensity increases, we reach a threshold where our mitochondria can no longer produce the amount of energy required as lactate and fat oxidation provide a lot of energy, but take longer to produce than energy from glucose. Here, fat oxidation drops sharply and glucose utilization rises sharply. Because the mitochondria are past their limits, lactate build-up in our blood increases.

Lactate Zone 4: This is where we start to think of exercise as high-intensity exercise and the blood will have lactate levels above 4mmol/L. Here glucose is nearing 100% of the fuel and fat oxidation drops down even further. There are big increases in lactate and it starts to accumulate heavily which is referred to as a lactate threshold.

Lactate Zone 5: Here even glucose is not fast enough to produce all the energy required, so we tap into ATP (energy stored in the muscles). With even higher lactate and ATP requirements, we can only hold this intensity for 2-3 minutes max.

Lactate Zone 6: This is all out sprinting and the main fuel is ATP. Not sustainable for very long.

Note: that as we increase here in zones, the power output is also increasing tremendously. So although the percentages of phosphagen, glucose, fat, and lactate, change relative to each other and relative to the total amount of energy required, there lactate and fat oxidation does not stop at high-intensity exercise. This is the point. At high intensity exercise, our mitochondria are still at work recycling lactate which is hugely beneficial, it is just happening at a level where our bodies are producing more lactate than we can recycle.

To build efficiency in our mitochondria, Lactate Zone 2 training is crucial. It just cannot be done effectively at higher intensities. Since the higher intensities have tons of value that Zone 2 training cannot provide, we want a functional fitness program that takes advantage of everything we know about Zone 2 training and high-intensity training.

We define a Lactate Zone 2 as an RPE 4-5, a slightly labored, but conversational pace, and something we feel like we could maintain for hours.
We incorporate 45 minutes or more of Lactate Zone 2 training 1-5 times a week. We have classes designed specifically for Lactate Zone 2 training and we also provide Marathon and Spartan Race prep run options that are to be performed mostly in Lactate Zone 2 (we’ll let you know when to go harder).
We separate our Lactate Zone 2 training from our high intensity training. If the goal is Lactate Zone 2 and we slip into Lactate Zone 3+, it may take a while for our bodies to get back fully into Lactate Zone 2, which detracts from the amount of Zone 2 training time, so high-intensity interval training where we spend time at lower heart rates and powers will likely not get our blood lactate levels back down into zone 2, so would not count.
After we get in our adequate minutes of Lactate Zone 2 training, afterwards, even immediately afterwards, it is OK to go into higher intensities. So, it is not considered minutes in Zone 2 training if it is recovering from higher intensity efforts, but feel free to finish lactate zone 2 training workouts hard (as long as you are taking fatigue management for your workout program into account).
Lactate Zone 2 Training Workout Examples:
- Target at least 45 minutes, but up to hours and hours for your Zone 2 workouts.
- Running, ruck walking, and indoor cycling, riding an air bike, rowing, stair-stepping, and walking on an inclined treadmill at an easy pace tend to work best. Outdoor cycling is great, but it’s hard to not get kicked into too high or low of a zone with hills and most people don’t have a power meter to assist in managing effort levels. If you’re not trying to be a professional athlete and you want to cycle outdoors, absolutely go for it, just walk or go super easy up hills! For running, depending on your level, you’ll likely need to walk up any hills to avoid kicking into higher zones.
- Use a combination of RPE, heart rate, and power meters to figure out a zone 2 pace for each of your exercises. If you are an experienced high intensity athlete, but with little low intensity experience, expect your heart rate to be much lower than the internet says until your body and mitochondria learn how to become more efficient with fat and lactate. A little bit of burn is OK, but you should not get a big pump.
- Increase your pace and power over time, staying at the same RPE levels.

When to incorporate Lactate Zone 2 Training?

At MovementLink, each week, at a minimum we recommend getting in at least:

1 x upper body specific workout that incorporates both
- upper body strength training and
- a short, high-intensity section that compliments the strength work.
1 x lower body specific workout that incorporates both
- lower body strength training and
- a short, high-intensity section that compliments the strength work.
1 x 45 minute or more lactate zone 2 workout.

There are many different ways to organize your workouts within the MovementLink workout program and may different options for adding workout days. You can get more specifics about the MovementLink program here, but the decision to add high-intensity workouts or zone 2 workouts are highly dependent on your interests and goals. In the case where the amount of workouts per week for an athlete extends beyond 6-7 workouts per week, our lactate zone 2 training workouts make for a great option for 2-a-days paired with a high-intensity workout. Here’s an example week of a very advanced athlete that dedicates a lot of training time to their fitness and health:

Monday
- Lower Body Strength + Lower Body High-Intensity Workout
Tuesday
- Lactate Zone 2 Ruck
- Lactate Zone 2 Workout with Max Intensity Finish
Wednesday
- Lactate Zone 2 Indoor Cycling
- Upper Body Strength + Upper Body High-Intensity Workout
Thursday
- Lactate Zone 2 Run
- Long Grind Medium to High Intensity Lower Body Workout
Friday
- Rest/Recover
Saturday
- Long Lactate Zone 2 Run
Sunday
- Long Grind Medium to High Intensity Upper Body Workout
- Lactate Zone 2 Indoor Cycling

As an event approaches, some of the 2-a-day workouts would shift into 1 event-specific training session.

Benefits of Cool-down

Let’s take a second to look at why we go for walk, slow jog, hop on a rower or bike to cool down. When we have developed the ability for our mitochondria to efficiently use lactate as a fuel source, after a high-intensity effort, if we put in very easy effort (lactate zone 1), like we’ve been talking about our mitochondria will pull lactate out of our blood to be used for the low effort and because the low effort is producing very little lactate on its own, this will have a large, net effect of reducing blood lactate after a workout.

Additional Ways to Improve Mitochondria Function:

With mitochondria function and efficiency being our primary reason to incorporate zone 2 training, we’d like to go ahead and mention that the MovementLink eating window, heat exposure, and cold exposure protocols also benefit mitochondria function. They are not a replacement, but can be a huge value add.