To grasp the concept of Zone 2 cardio, it's essential to comprehend how your body utilises the nutrients you consume to power your daily activities.
All the cells in your body rely on adenosine triphosphate (ATP) for energy. Whether you're walking, deadlifting, or even reading this article, ATP is at work.
ATP can be produced through three different pathways:
Oxygen-Dependent Metabolism (Oxidation): This is the primary way your body creates ATP during the day. When you breathe, oxidation transforms fatty acids into ATP, generating a substantial amount of energy. This process occurs within the mitochondria of your cells, making it crucial for Zone 2 cardio.
Non-Oxygen-Dependent Glucose Metabolism (Glycolysis): During intense exercises like sprinting or weightlifting, your body switches from using fatty acids to burning glycogen (carbs) to replenish ATP stores. While glycolysis produces a significant amount of ATP, it occurs in the cytosol of your cells, not in the mitochondria.
Recycling of Previously-Stored ATP: As ATP transfers energy to cells, it loses one of its phosphates and becomes adenosine diphosphate (ADP). Creatine then steps in and provides its phosphate group, converting ADP back into ATP for reuse. Creatine supplementation can enhance this process.
It's worth noting that ATP can also be obtained from lactate, a fascinating but technical process wherein the body converts lactate into glucose for use in glycolysis.
Exercise scientists have established "training zones" to help athletes and coaches understand the energy systems and muscle fibers utilised at various exercise intensities. These zones range from Zone 1 (lowest intensity) to Zone 5 (highest intensity depending on which scale you use).
Zone 1: Energy Source: Primarily fat
Zone 2: Energy Source: Fat with a trend towards carbohydrates
Zone 3: Energy Source: Increasing reliance on carbohydrates while still using fat
Zone 4: Energy Source: Mainly carbohydrates
Zone 5: Energy Source: Almost exclusively carbohydrates
In Zone 1 and 2, you primarily use fat as the main energy source, gradually shifting to carbohydrates as you progress to Zone 3. By the time you reach Zone 5, you will almost exclusively using carbohydrates as your fuel source.
Zone 2 cardio involves exercising at an intensity level that optimally stimulates your cells' mitochondrial function. This means you meet your body's ATP demands using fat and oxygen within the mitochondria. If you increase the intensity slightly, your body will start using more carbs from the cytosol to create ATP through glycolysis.
Interestingly, many recreational athletes tend to skip Zone 2 and opt for zones 3, 4, or 5, where carbohydrates become the primary fuel source. This inclination toward higher-intensity training has become prevalent over the past decade, as there is a misconception that exercise needs to be painful and uncomfortable to be effective.
Zone 2 is often overlooked because it feels deceptively easy. People tend to run at a pace that leaves them huffing and puffing, thinking it's a normal effort, but they're likely already in Zone 3 or higher.
Contrary to popular belief, Zone 2 cardio is not painful or uncomfortable. In fact, you can sustain this intensity for extended periods without much strain. Nevertheless, numerous studies indicate that neglecting Zone 2 cardio can cause you to miss out on numerous health and performance benefits.
The Advantages of Zone 2 Cardio Training
Enhances Mitochondrial Quantity and Efficiency: Zone 2 is the optimal intensity level for stimulating your mitochondria to produce ATP. By spending more time in Zone 2, your body responds by generating more mitochondria, which boosts the capacity for ATP production through fat oxidation. Improved mitochondrial efficiency contributes to better energy utilisation, promoting overall health and longevity.
Improves Endurance Performance: For endurance athletes like runners and cyclists, increasing Zone 2 cardio time results in enhanced performance. Elite athletes have been utilising Zone 2 training for decades, with about 80% of their workouts spent in this zone. Although it might not feel like intense effort, it significantly improves athletic abilities, allowing you to go faster and longer while maintaining a low heart rate. The training enhances the body's fat-burning capacity, enabling sustained pace and performance due to the nearly unlimited fat supply.
Enhances Cardiovascular Health: Zone 2 cardio not only exercises the mitochondria but also benefits the heart and circulatory system. The heart becomes stronger, requiring fewer pumps to circulate blood efficiently, while the vascular system expands, ensuring improved oxygen delivery to various body parts. This heightened cardiovascular fitness leads to better exercise performance and a lower resting heart rate.
Increases Work Capacity: For strength athletes, Zone 2 cardio aids in faster recovery between lifting sets, enabling you to accomplish more work during training sessions. Incorporating Zone 2 training can reduce fatigue and breathlessness during strength workouts, maximising productivity within the allocated time.
Prevents Injury and Aids Recovery: Zone 2 training places minimal stress on the body, allowing you to add volume to your training routine without risking injuries or exhaustion. It serves as excellent "active recovery exercise," promoting nutrient delivery to muscles and aiding in recovery from intense weightlifting sessions or injuries.
Enhances Mood: Zone 2 cardio positively impacts mood and mental well-being. Engaging in this form of exercise releases feel-good endorphins, promoting a sense of well-being and satisfaction. The gentle muscle movement and improved blood circulation contribute to a fantastic feeling after the workout.
How to Identify If You're in Zone 2 Cardio
To achieve the optimal intensity of Zone 2 cardio, you want to exercise at a level where you predominantly use fat oxidation for energy, maximise mitochondrial function, and avoid switching to burning carbs, maintaining a boundary close to Zone 3 without crossing over.
Here are various methods to determine if you are in this cardiovascular sweet spot:
Heart Rate Method: Track your heart rate while exercising to identify if you're in Zone 2. Typically, your heart rate should be around 70-80% of your maximum heart rate. To find your maximum heart rate, you can either perform a max heart rate test on a treadmill or stationary bike, or estimate it based on the formula: 220 minus your age.
Maffetone Formula: This formula, developed by Phil Maffetone, provides a heart rate that corresponds to the upper limit of Zone 2. Subtract your age from 180, and adjust based on certain factors, such as illness, overtraining, or training experience. Although not highly accurate, it will give you a general Zone 2 heart rate range.
Talking Test: A simple and surprisingly accurate method involves the "talking test." In Zone 2, you can comfortably hold a conversation but may sound slightly breathy. While talking may not be as clear as at rest, you can still communicate without extreme difficulty.
Measure Your Lactate: The most precise way to confirm Zone 2 cardio is to measure your lactate levels after the training session. If your lactate falls between 1.7 and 1.9 mmol, you were likely in Zone 2. However, this method requires a drop of blood and expensive test strips.
In practice, a combination of the Maffetone formula and the talking test is often used. The Maffetone formula helps determine an approximate Zone 2 heart rate, while the talking test helps refine the intensity during the workout.
How to Incorporate Zone 2 Cardio into Your Routine
You have the freedom to choose any exercise modality that you enjoy for your Zone 2 cardio. Whether it's running, cycling, or using cardio machines like the cross trainer, the key is to maintain your heart rate within the Zone 2 parameters consistently.
Exercises that involve full-body, high exertion, like running and swimming, might be challenging for Zone 2 cardio, especially for beginners. Instead, opt for less taxing forms of cardio, such as cycling or using cardio machines with steady pace/resistance/incline settings. This allows you to keep your heart rate within the desired range more easily.
When starting your workout, begin slowly as your heart rate tends to spike initially. Allow your heart to settle into a steady rhythm before worrying about staying within Zone 2. Aim for each Zone 2 session to be at least 45 minutes long.
While indoor workouts on treadmills or cardio machines are efficient for maintaining steady heart rates, outdoor Zone 2 cardio can be especially beneficial for mental health. Running outdoors in nature, while keeping your heart rate in Zone 2, provides an opportunity to find flow and clear your mind. It can serve as a time for reflection and creative thinking.
If you want to transition your Zone 2 runs outdoors, build your Zone 2 fitness base by walking on an inclined treadmill. Gradually progress to jogging on a flat treadmill while maintaining Zone 2 heart rate. As you advance, increase your pace while keeping your heart rate steady in Zone 2.
When you feel ready, take your running outside. Start with a flat course, and once you can maintain Zone 2 on flat terrain, gradually incorporate hilly routes. However, be prepared that some steep hills might require walking to stay within Zone 2, regardless of your fitness level.
How Much Zone 2 Cardio Should You Aim For?
The recommended amount of Zone 2 cardio per week varies, but aiming for 150 to 180 minutes is generally considered a good minimum. According to Dr. Iñigo San-Millán, for optimal mitochondrial benefits, each session should be at least 45 minutes long.
So, if you plan to do 180 minutes weekly, you could divide it into four 45-minute sessions or opt for a single longer session – whichever suits you best.
While the ideal goal is to have the majority of your cardiovascular exercise in Zone 2 – around 80% – any amount of Zone 2 cardio is beneficial. If you can't manage 180 minutes a week, don't worry; do what you can.
Remember, doing a small amount of high-intensity cardio is still important for overall health, fitness, and athletic performance. Incorporating one weekly high-intensity interval training (HIIT) session, where you go all-out, should suffice.
It's crucial to avoid the "garbage zone," as coined by Peter Attia, where your exercise intensity is neither high enough for anaerobic fitness nor low enough for aerobic fitness improvements.
Instead, challenge yourself during intense workouts and spend the rest of your exercise time in the slow-and-steady, health and performance-enhancing Zone 2.
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