Unlocking the Benefits of Zone 2 Training

Zone 2 training has become quite a buzzphrase in fitness circles recently. In fact, it’s become somewhat of a hot topic, with some people claiming it’s the ideal cardio training format while others see it as nothing more than a convenient excuse to take it easy during workouts.

As a seasoned personal trainer, I’ve had my share of clients who were skeptical about the lack of intensity involved with Zone 2 training. However, the proof, as they say, is in the pudding. Results made believers out of each one of them.

My purpose in this article is to lay out the research-backed benefits of Zone 2 training and show you how to implement Zone 2 into your training program. Here’s what we’ll cover:

• What is Zone 2 Training?
• Zone 2 Training & Muscle Fiber Recruitment
• Benefits of Zone 2 Training
• Zone 2 Training Application
• Common Mistakes to Avoid in Zone 2 Training
• FAQs

What is Zone 2 Training?

Technically, the Zone 2 training effort keeps your lactate levels below 2 millimoles (mmol) during cardio exercise. In this zone, your body will begin to produce a little bit of lactate, but it can clear it out. This allows you to continue training for an extended period without muscular exhaustion.

To accurately gauge whether you are in Zone 2, you’ll need to be attached to a lactate monitor. However, there are other ways to determine whether you’re within the Zone 2 range, including:

• You should be able to comfortably breathe in and out through your nose without forcing your breath.
• You should be able to maintain a conversation, though not as easily as if you were walking.
• Your heart rate should be 60-70% of maximum. 

To determine your max HR, subtract your age from 220. For example, if you are 32, your calculation would be as follows:

The Heart Rate Zones

There are five heart rate training zones, each corresponding to a different level of effort. Each zone is based on a percentage of your maximum heart rate, just as in the zone 2 example we looked at. 

The zone heart rate percentages are:

• Zone One: 50-60% of Max HR (walking)
• Zone Two: 60-70% of Max HR (light jogging)
• Zone Three: 70-80% of Max HR (medium-paced running)
• Zone Four: 80-90% of Max HR (fast running)
• Zone Five: 90-100% of Max HR (full-send sprinting)

Zone 2 Training & Muscle Fiber Recruitment

Your muscles comprise two types of fiber:

• Slow twitch (Type 1)
• Fast twitch (Type 2)

These fibers follow a set recruitment pattern so that slow twitch fibers are recruited first. Then, as the activity becomes more intense, fast twitch fibers are brought into action. 

So, when we exercise at the lower training zones, we are almost exclusively using slow twitch fibers. It’s only when we move into Zone 3 and beyond that fast twitch fibers come into play. 

Fast and slow twitch muscle fibers also have different chemical make-ups, which affects the way they behave. Slow twitch fibers have much more mitochondria with a greater capacity to convert fats rather than carbohydrates into energy. 

Here’s a chart contrasting fast and slow twitch muscle fiber activity at various training zones:

Training Zone	Main Energy Source	Type of Fiber Recruited
Zone 1	Fats	Slow Twitch
Zone 2	Fats	Slow Twitch
Zone 3	Fats and Carbs	Slow and Fast Twitch
Zone 4	Carbs	Fast Twitch
Zone 5	Carbs	Fast Twitch

Benefits of Zone 2 Training

Zone 2 training challenges the idea that greater intensity brings greater rewards. As a result, some people find it difficult to understand how maintaining a low to medium intensity can benefit them. Here’s the breakdown:

Better Aerobic Capacity

Training in Zone 2 improves how your body uses oxygen. It improves your VO2 max, which indicates your oxygen capacity. This improves cardiovascular health because your heart doesn’t have to work as hard to supply oxygen to your cells.

A 2019 study published in the International Journal of Exercise Science looked at the difference in aerobic training intensity and volume in relation to VO2 max and other aerobic health markers. [1]

Thirteen triathletes participated in running and cycling workouts for eight weeks. Groups were divided according to training volume and intensity. The group that trained at a lower intensity for a longer time had a significant VO2 max increase than the other group. 

Fat Burning

To appreciate the fat-burning benefits of Zone 2 training, we need to zoom in on what happens in our muscle fibers when we exercise. During Zone 2 training, our slow twitch (type-1) muscle fibers are activated more than our fast twitch (type-2) fibers. 

We can only burn fat while exercising when we activate the mitochondria in slow-twitch fibers. As a result, Zone 2 training results in the highest level of fat oxidation; that’s the process by which fat is broken down into energy. 

A 1994 German study examined the effectiveness of aerobic exercise for fat burning. The main finding was that the highest fat oxidation rates occurred at low to moderate cardio intensity levels, equating to Zone 2 training. [2]

Promotes Recovery

Lactate is a byproduct of energy creation. When we exercise, it builds up in our muscle cells. At Zone 2, though, the body can remove lactate at the same rate it is produced. As a result, we don’t get the build-up in fatigue that happens at higher zones.

When you have a lactate build-up during your workout, your recovery ability is negatively affected. So, the low lactate output in Zone 2 not only allows you to continue training with less fatigue but also improves your post-workout recovery. 

The improved oxygen uptake that Zone 2 training provides also helps with recovery. You’ll be taking more oxygen into your body and transporting it more efficiently to your muscle cells while exercising and during the recovery phase. 

The improved cardio functioning this type of training promotes will also get those vital post-workout nutrients like protein and carbs to your muscles faster. 

Increase Insulin Sensitivity

The better your insulin sensitivity, the more effectively your body will use the hormone insulin to transport glucose (blood sugar) into your muscle cells. Training at Zone 2 appears to be the most effective zone to increase insulin sensitivity. 

A 2016 meta-study focused on the difference between low-medium intensity and high-intensity aerobic exercise in relation to insulin sensitivity. The results confirmed that moderate-intensity (zone 2) training improves insulin sensitivity more than high-intensity training. 

The researchers hypothesized that the improved insulin sensitivity may be due to the enhanced fat oxidation during low-moderate aerobic exercise. [3]

Improves Mitochondrial Efficiency

Mitochondria are the engine that drives energy production in your cells. They break down fats and carbs to produce adenosine triphosphate (ATP), the energy currency that fuels your workouts.

Improved insulin sensitivity and greater VO2 max make your mitochondria work more efficiently. As we’ve already seen, Zone 2 training improves both variables. That’s why training in this zone boosts your mitochondrial function.

Interestingly, training at Zones 4 and 5 may negatively affect mitochondrial efficiency. A 2021 study showed that high-intensity interval training (equating to Zone 5) resulted in less efficient mitochondrial function, along with reduced glucose tolerance. [4]

Zone 2 Training Application

Zone 2 training works with aerobic exercise as long as you stay in the zone. A machine with an accurate heart rate sensor makes this a lot easier. Some options include a rowing machine, treadmill, ski erg, or elliptical. 

If you prefer a form of exercise that doesn’t have a way to check your pulse (and you’re not wearing a heart rate monitor), you can simply use the talk test. In Zone 2, you should be able to maintain a conversation but with some difficulty.

If you can chat comfortably, you’re probably in Zone 1, and if you can’t complete a sentence, you’ve probably pushed into Zone 3.

Zone 2 Training Frequency

If you’re new to Zone 2 training, I recommend starting with three 20-minute weekly sessions. After a month or two, when you’ve built up your aerobic base, increase the time by 10% per week. 

Common Mistakes to Avoid in Zone 2 Training

As a personal trainer, I see many common mistakes during Zone 2 training. Here’s a rundown of the five biggest ones, along with tips to overcome them:

Mistake #1: Over-Reliance on Zone 2 Training

Many people enjoy Zone 2 training because it allows them to train within their comfort zone. As a result, it’s the only form of exercise they do. I often see this at the gym, where people come in, do 30 minutes of Zone 2 training on the treadmill, and then leave.

While these people are getting cardiovascular and fat-burning benefits from their training, they’re also missing a lot of benefits that they’d get from a more holistic program. 

By adding strength, balance, flexibility, explosiveness, and mobility training, you will enhance your total fitness, increase your longevity, and become a far more functional individual. 

A holistic training plan needs to balance each of these key fitness areas. Let’s use the example of a 32-year-old woman who’s gotten into the habit of just doing 30 minutes of Zone 2 at the gym five days per week. Here’s what I’d suggest she do to make her training more holistic:

• Cut back to three 30-minute Zone 2 sessions on the treadmill per week.
• Add two 30-minute strength training sessions on the days she’s not doing Zone 2 cardio.
• Finish each strength training session with a 5-minute HIIT workout in Zone 4 or 5.
• Follow up two of her Zone 2 treadmill sessions with 10 minutes of plyometric mobility/explosiveness training.

Mistake #2: Doing Too Much, Too Soon

Zone 2 training seems relatively easy than HIIT or a balanced strength training program. As a result, it’s easy to do too much of it before your body is ready. This results in overtraining, which can lead to a plateau or increase injury risk.

Your training volume must align with your fitness level and experience. If you’re just starting your fitness journey, three 20-minute Zone 2 sessions per week will be plenty. Of course, you should switch between different training modalities, as mentioned in the previous section. 

Start with a relatively easy Zone 2 volume and build progressively each week. During the first couple of months, you’ll be building your aerobic base. After this, I recommend increasing your Zone 2 training volume by 10% weekly. 

You should also build active recovery weeks into your Zone 2 training schedule. This involves dropping the volume by 30-40%. Do this once every six to eight weeks. It gives your muscles and nervous system time to recover.

Mistake #3: Not Listening To Your Body

We’ve already considered the criteria for determining if you’re training within Zone 2, with the main one being to stay within 60-70% of your max heart rate. However, you should also take your body’s cues into account. This type of cardio training brings some unique variables into play that you need to pay attention to. These include:

• Dehydration
• Insufficient recovery
• Environmental conditions, such as excessive heat
• Stress

These factors may artificially elevate or decrease your heart rate. For example, you could work at your normal Zone 2 level of exertion but realize it’s not enough to stay within the zone. 

Rather than automatically adjusting your intensity to bring the heart rate up or down, you need to have the ability to assess your body’s variables and decide if they are the reason you’re slightly out of the zone. That’s how you listen to your body while working out. 

Zone 2 Training FAQs

Is Zone 2 walking or jogging?

Light walking will not raise your heart rate enough for Zone 2 training. However, brisk walking or light jogging probably will. In a Zone 2 workout, you should be able to hold a conversation but with some difficulty. 

Should I train in Zone 2 or 3?

Zone 2 training is best to build an aerobic base. It will also burn more fat for energy than Zone 3. However, Zone 3 is better for building up your aerobic endurance. Ideally, you should be doing both types of cardio training. The ratio will depend on your training goals. 

Is Zone 2 better than HIIT?

Whether Zone 2 is better than HIIT depends on your training goal and the type of training you prefer. Zone 2 will burn more fat for energy than HIIT, which is at Zone 4 or 5. It will also better improve your aerobic endurance and is more joint-friendly.

On the other hand, HIIT is more time efficient, provides a greater metabolic boost, and does a better job of improving your anaerobic fitness. 

Conclusion

Moderate intensity, or Zone 2 training, took a big hit with the massive popularity of HIIT training. With recent studies to back it up, however, it’s come back strong. By adding a few Zone 2 sessions to your weekly training program, you’ll reap its many benefits. 

References

1. Neufeld, E. V., Wadowski, J., Boland, D. M., Dolezal, B. A., & Cooper, C. B. (2019). Heart Rate Acquisition and Threshold-Based Training Increases Oxygen Uptake at Metabolic Threshold in Triathletes: A Pilot Study. International Journal of Exercise Science, 12(2), 144–154. PMID: 30761193, PMCID: PMC6355121. Published online 2019 Jan 1.
2. Knechtle, B. (2002). Exercise intensity and fat burning–theoretical principles and practical considerations. Praxis (Bern 1994), 91(21), 915-919. doi:10.1024/0369-8394.91.21.915. PMID: 12085547
3. McGarrah, R. W., Slentz, C. A., & Kraus, W. E. (Year). The Effect of Vigorous- Versus Moderate-Intensity Aerobic Exercise on Insulin Action. Journal Name, Volume(Issue), Page numbers. DOI: 10.1007/s11886-016-0797-7. PMID: 27796854.
4. Flockhart, M., Nilsson, L. C., Tais, S., Ekblom, B., Apró, W., & Larsen, F. J. (2021). Excessive exercise training causes mitochondrial functional impairment and decreases glucose tolerance in healthy volunteers. Cell Metabolism, Volume(Issue), Page numbers. DOI: 10.1016/j.cmet.2021.02.017.

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