What Are the “Zones” and What the Hell Is Z2 That Everyone Keeps Talking About?

If you've been involved in the fitness community lately, you've likely encountered terms such as "Zone 2" or "Z2" training. This interest has grown in part due to the increasing popularity of wearables, which has sparked a greater focus on heart rate (HR) data. In this blog, I aim to explain the science behind these zones and how you can utilize them for more effective training. So, what exactly are these "zones," and why has Z2 become so popular and what benefit it brings to hybrid athlete? Let's dive into it.

The Basics: What Are Training Zones?

Training zones are a way to measure and describe exercise intensity, based on heart rate. The idea is to divide your effort into “zones,” each corresponding to a percentage of your maximum capacity. Most systems use five zones, but zones can also be divided into 3 or even 7. The core concept is still the same; it answers the question: What energy source is your body (mainly) using?

Energy sources / energy production systems

In the physical world we live in, everything requires energy. When we move our muscles, we need chemical energy. As a matter of fact, muscle contraction is a series of chemical reactions. To simplify this complicated process: every movement requires "fuel" called ATP (adenosine triphosphate) that we create either aerobically (with air) or anaerobically (with lactates). The intensity of the workout defines how the energy is produced. The higher the intensity, the more we lean on the anaerobic side, and when we are still or moving with light intensity, we use the aerobic side.

The range from 0-100 is divided to 5 zones for practical reasons but it is characterized by two key thresholds: Lactate threshold 1 and Lactate threshold 2. The first threshold marks the point where lactate levels begin to rise, known as the "Aerobic threshold," which signifies the end of the aerobic range and consequently the end of the well-known Z2 zone.

The second threshold (LT2) is the point where lactate buildup exceeds the body's capacity to use it. This threshold marks the boundary of your maximum work capacity and can be maintained only for a few minutes.

So whats the big deal then?

The primary distinction between these zones lies in the energy source your body utilizes. When the body primarily relies on the aerobic system, it mainly uses fats as the energy source. This allows the activity to be sustained for a longer period since our bodies store a significant amount of energy as fats. This is why it is referred to as the "fat burning zone," although this term can be misleading. For weight loss, it is more crucial to focus on total energy expenditure and maintaining a caloric deficit.

When the intensity exceeds LT1, your body depends more on carbohydrates for energy. Thus, replenishing these stores is essential for hybrid athletes during high-intensity exercise.

Zone 1 (Z1): 50-60% of HR max. Very light effort, like an easy walk or casual cycling. Does not have a performance-improving effect, although it can improve recovery by increasing blood flow.

Zone 2 (Z2): 60-70% of HR max. Light to moderate effort, where you can hold a conversation but still feel like you’re working. This is your aerobic sweet spot. This is where your ability to produce energy aerobically will grow the most!

Zone 3 (Z3): 70-80% of HR max. Moderate to hard effort, where talking becomes challenging. Often called the “grey zone” because it’s not quite hard enough for major anaerobic benefits but too hard for proper aerobic base training.

Zone 4 (Z4): 80-90% of HR max. Hard effort, close to your lactate threshold. Speaking in full sentences becomes impossible. This is called threshold often because it is at the end of aerobic range. Suistanaible for 1-2 hours.

Zone 5 (Z5): 90-100% of HR max. Maximal effort, short bursts of intense activity where you’re gasping for air.

Why Is Z2 Training So Important?

1. Aerobic Base Building

Z2 training strengthens your aerobic energy system, which powers most of your daily activities and longer workouts. This system improves your body’s ability to use oxygen efficiently, increasing your endurance and overall energy production capacity.

2. Faster Recovery

A strong aerobic base enhances recovery by replenishing the energy stores faster. This means you can bounce back quicker between workouts or even during intervals in the same session. Also greater aerobic capacity is linked to higher HRV and better night time recovery.

3. Fat Utilization

At Z2 intensity, your body predominantly uses fat for fuel, which is more sustainable than relying on carbohydrates only. This can improve metabolic health and increase your ability to sustain long efforts without hitting the infamous “wall.”

4. Cardiovascular Health

Z2 training reduces stress on your body compared to high-intensity sessions. The stress response after a high-intensity session is remarkably higher.

5. Sustainability

Unlike high-intensity training, which can lead to burnout if overdone, Z2 is sustainable for long periods. You can safely include it in your routine multiple times a week without excessive fatigue.

Common Misconceptions About Z2

“It’s too easy to matter!”

Z2 might feel easy, but that’s the point. Its effectiveness comes from consistent, lower-intensity efforts that gradually build endurance over time.

“I need to feel exhausted for a workout to count.”

This “no pain, no gain” mindset leads many to overtrain or neglect aerobic base building. Z2 is proof that training smarter beats training harder.

“I’m too fit for Z2.”

Even elite athletes dedicate 70–80% of their training volume to Z2. If it works for them, it works for you.

How to Get Started with Z2 Training

1. Determine Your Zones

Use a heart rate monitor or fitness tracker to estimate your maximum heart rate and calculate 60–70% of that value. Alternatively, use the talk test—if you can speak comfortably, you’re likely in Z2.

2. Plan Your Sessions

Start with 30–60 minutes of Z2 training, 2–3 times a week. Activities like jogging, brisk walking, cycling, or swimming work well.

3. Be Consistent

The real benefits of Z2 come from consistency over weeks and months, not a single session.

Why Hybrid Athletes Should Care

For hybrid athletes—those balancing strength and endurance—Z2 training is the glue that holds it all together. It supports recovery from heavy lifting, improves stamina for endurance events, and creates a foundation for long-term performance. Incorporating Z2 into your hybrid training program ensures you’re not just strong or enduring, but resilient and adaptable across all physical challenges.

So, the next time you hear someone rave about Z2, you’ll know exactly why it’s worth the hype—and why it should be a staple in your training program.