Why Zone 2 Cardio is Optimal for Improving Overall Fitness and Health

Why Zone 2 Cardio is Optimal for Improving Overall Fitness and Health

By Brian Saulon

Many of us categorize cardiovascular training into 2 groups, aerobic and anaerobic. Anaerobic exercise is high intensity at a short duration without the utilization of oxygen e.g., sprinting, high-intensity interval training, and circuit training. Aerobic exercise is associated with low intensity at longer durations with the utilization of oxygen, like running, swimming, and cycling. All of this is important when considering your training goal which leads us into the topic of the various heart rate training zones and why Zone 2 training can be an essential tool in your belt.

Cardiovascular training is an essential component of any well-rounded fitness routine. It helps to regulate blood pressure, aids in weight loss, improves endurance, and strengthens the immune system (Milnea, 2023). However, not all workouts produce the same results. Zone 2 cardiovascular training, also known as aerobic or endurance training, has accumulated significant attention due to its benefits for overall health and fitness and, more specifically, its ability to improve mitochondrial function within the body which leads to energy being produced more efficiently, an increase in fat breakdown, and prevention of certain diseases. In this article, we will thoroughly explore all aspects of Zone 2 training, including what distinguishes the different heart rate training zones, how they can benefit all populations, the significant effects on the body's mitochondria, and much more. 

Heart Rate Training Zones: 

Before we can dive into Zone 2 training, it’s important to fully understand the different heart rate training zones. Heart rate training zones are referred to as a percentage of maximum heart rate for a given individual, or the highest rate the heart beats per minute during exercise. The various heart rate training zones are also distinguished by the energy sources and muscle fibers the zone utilizes. At lower to moderate intensities, Type 1 muscle fibers are recruited and utilize more fat stores to produce energy. At moderate to higher intensities, Type 2 muscle fibers are engaged and the body transitions to primarily using carbohydrates to generate energy (Attia & Attia, 2022).

Zone 1:

Zone 1 training is the minimum stimulation the muscle fibers receive. For example, this can be a simple stroll down the street or active recovery and is done at a very low intensity (Attia & Attia, 2022). Specifically, it is 50-60% of an individual's heart rate max and utilizes fat as the main substrate. 

Zone 2:

Zone 2 training is the “highest level of exertion in which you can still carry out a conversation (Attia & Attia, 2022).” This is done at low intensities at 60-70% of an individual’s heart rate max and utilizes mainly fat and little carbohydrate. Exercise done at this intensity should also be somewhat uncomfortable. 

Zone 3:

Zone 3 training is done at moderate intensities of 70-80% of an individual’s heart rate max. It is said to be a transition period due to the main source of energy switching to mainly carbohydrates and little fat (Attia & Attia, 2022).

Zone 4:

Zone 4 training is done at high intensity at 80-90% of an individual’s heart rate max. At this zone, there is zero fat oxidation which means that the body is not burning fat anymore, but is depending on glucose to fuel exercise (Attia & Attia, 2022).

Zone 5:

Zone 5 training is done at very high intensity at 90-100% of an individual’s heart rate max with the main source of energy coming from carbohydrates. For example, sprinting at maximum intensity would be characterized as zone 5 training. 

How to calculate your own age-predicted maximum heart rate:

Because the majority of people do not have access to a lactate meter to measure Zone 2 capacities, knowing your heart rate maximum can be a good indicator for distinguishing exercise intensities.

In order to begin zone training, we must first be able to calculate our own age-predicted maximum heart rate to ensure we are training within the correct parameters (Haff & Dumke, 2018). We can do so by utilizing the following equation:

208 - (0.7 x Age) = APMHR 

This will give us a proper value in order to determine which training zone we’re in at a given time.

What is Zone 2 Training:

Zone 2 training involves exercising within a particular range in heart rate that targets the aerobic system. As mentioned previously, Zone 2 training occurs in 60-70% of an individual’s age predicted maximal heart rate, but can be dependent on age, fitness level, and overall health status. It is done at low to moderate intensities for longer periods of time and utilizes fat as the main fuel source although there is some carbohydrate oxidation as well (Attia & Attia, 2022). Training in this zone can be quite beneficial for those who want to lose fat, improve body composition, and increase their aerobic and cardiovascular health and endurance. 

Dr. Peter Attia mentions in his podcast with Dr. Iñigo San Millán about “Zone 2 Training and Metabolic Health,” that when someone trains in this heart rate zone, the body requires the recruitment of Type 1 muscle fibers at an aerobic level. Type 1 muscle fibers, also known as slow-twitch muscle fibers, have the highest mitochondrial density and content in comparison to Type 2 muscle fibers. Their ability to break down fat is much greater than Type 2. In aerobic capacities, the body produces energy at a sufficient pace to allow for the breakdown of primarily fatty acids in the mitochondria to meet all the metabolic demands. On the contrary, at higher intensities, we begin to become anaerobic which recruits Type 2 muscle fibers. Type 2 muscle fibers, or fast-twitch muscle fibers, are known to have a “lower mitochondria content because they don’t necessarily need the mitochondria to break down glucose, they can actually do so in the cytosol of the cell (Attia & Attia, 2022). In anaerobic levels, the mitochondria can no longer produce as much energy as the body needs; therefore, as we become more consistent in Zone 2 training, the increased recruitment of Type 1 muscle fibers will have a progressive and significant effect by further developing mitochondrial performance in the body (Attia & Attia, 2022).

Benefits of Zone 2 Training:

1. Increases Mitochondrial Quantity, Activity, Versatility, and Effectiveness
   • Mitochondria are in charge of generating adenosine triphosphate (ATP) or energy, which is crucial for sustaining proper organ function, cognitive function, and muscle endurance, as well as our general health. It has been demonstrated that consistent Zone 2 exercise increases mitochondrial biogenesis, or the process by which your body makes more mitochondria (Lim et al., 2022). Therefore, your body produces more energy and has improved cellular function overall. This will cause the body to undergo less fatigue and be able to sustain higher intensities for longer. 
2. Increase the Ability to Break Down Different Substrates
   • As Dr. Peter Attia illustrates in his podcast, Zone 2 training allows the body to utilize fat more effectively for a longer period of time. This is due to the recruitment of Type 1 muscle fibers which are responsible for the breakdown of fat for fuel. It will increase our ability to conserve glycogen which is important in the regulation of blood sugar levels and the sustainability of exercise at higher intensities. Simultaneously, it will decrease insulin resistance and increase insulin sensitivity. A decrease in insulin resistance will keep blood sugar in a normal range and can prevent the body from developing conditions such as Type 2 diabetes or cardiovascular disease. Increasing insulin sensitivity makes it easier for the body to uptake glucose when needed (Attia & Attia, 2022).
3. Increases in Fat Loss
   • Zone 2 training is also effective for eliminating body fat. During Zone 2 training, the body uses fat as its main source of energy as opposed to carbohydrates. Because the intensity is at a low to moderate level, the body will burn the fat more effectively without using the stored glycogen (Attia & Attia, 2022). Due to this factor, Zone 2 training can be very effective for those looking to lose weight and increase body composition.
4. Less Risk for Injury
   • Higher training zones require much more from an individual. These intensities have more muscular demand. At higher intensities, there is a higher chance of being injured. Because Zone 2 training occurs at lower intensities and steadier paces, it’ll be a much safer stimulus to use when considering risk of falling, especially in older populations.
5. Improves Cardiovascular Health
   • Aerobic exercise positively correlates with increases in cardiovascular health and with VO2 max and cardiac output. As we incorporate more Zone 2 training, the heart will get stronger and more capable of efficiently pumping blood throughout the body. In the process, resting heart rate will be lower and sustainability of exercise-induced heart rate at a given intensity will increase (Milnea, 2023).
6. Increases Endurance
   • Training in Zone 2 is exceptional for increasing endurance. The body improves its ability to use oxygen to make energy by engaging in this kind of workout.  People may train for extended durations without getting exhausted as a result (Attia & Attia, 2022). Because of this, Zone 2 training is exceptional for all sorts of different fitness goals and for people of all ages. 
7. Improves Performance in Zones 3, 4, and 5
   • By training in Zone 2, we are developing an aerobic base, improving mitochondrial function, and building a foundation of endurance that will make training in Zones 3, 4, and 5 much easier (Attia & Attia, 2022).
8. Live Longer with Fewer Health Complications
   • Zone 2 training keeps our heart and mitochondria healthy, which in turn keeps us at lower risks of various diseases, such as diabetes, heart disease, and stroke (Díaz-Vegas et al., 2020). This is due to the fact that it enhances the functioning of your heart and blood vessels while also lowering inflammation within the body.

The Effects of Zone 2 Training on The Mitochondria

Mitochondria are small organelles found within the cell primarily known for creating the energy our bodies require everyday of our lives. There is a common misconception that mitochondria only have this single role in which it provides us with energy or ATP, but there’s actually so much more it does for the body. Firstly, by producing energy more efficiently, there are less reactive oxygen species (ROS) being produced which can be extremely harmful to DNA and even cause the advanced degradation of cells (Javadov et al., 2020). This will be a preventative measure when it comes to non-communicable diseases. Secondly, the mitochondria primarily utilize fat as a driving source to make energy which will allow the breakdown of fat to increase causing weight loss. And because the mitochondria play a vital role in cellular life and death, an increase in mitochondrial dysfunction can play a big part in developing obesity, insulin resistance, type 2 diabetes, cancer and cardiovascular disease (Díaz-Vegas et al., 2020).

1. Improve Mitochondrial Response
   • Training in Zone 2 increases the effectiveness of mitochondrial respiration, the method through which cells use oxygen to produce energy. This increase in mitochondrial respiration has a positive effect on the efficiency of the mitochondria (Lim et al., 2022). As a result, there is a decrease in the risk of NCDs linked to oxidative stress and poor production of energy (Díaz-Vegas et al., 2020). 
2. Increased Breakdown of Fat
   • Training in low to moderate intensities like Zone 2 training requires the utilization of fatty acids as the main substrate (Attia & Attia, 2022). Consistent Zone 2 exercise engages the adipose tissue-based enzymes that break down fat stores and promotes its movement into the mitochondria. These lipids go through a metabolic process called beta-oxidation once they are within the mitochondria, which turns them into energy that the body can use when it needs to. By exercising in Zone 2, you maximize your body's capacity to burn fat for energy, which promotes enhanced fat oxidation, better weight control, and improved metabolic health (Attia & Attia, 2022).
3. Prevention of Certain Non-Commnicable Diseases
   • Mitochondria has a direct role in the progression and degradation of our cells, or cellular aging. If the mitochondria are healthy, they’ll lessen the degrading effects. Conversely, if the mitochondria are dysfunctional, it can aggravate or intensify the aging process (Javadov et al., 2020). In that regard, mitochondrial dysfunction can actually be associated with the development of certain non-communicable diseases. These include cancer, obesity, cardiovascular disease, type 2 diabetes, and even insulin resistance. By improving the efficiency and health of the mitochondria by training in Zone 2, the cells will remain in homeostasis and defended from oxidative stress. Decreased risk of non-communicable diseases has been correlated with lower levels of oxidative stress (Díaz-Vegas et al., 2020).

How Often Should We Train Zone 2?

On Dr. Peter Attia’s podcast, Dr. Iñigo San Millán says when it comes to Zone 2 training, 3 to 4 times a week is generally recommended for the average person (Attia & Attia, 2022). This frequency gives an adequate amount of time for recovery and adaptability while still allowing for an adequate training stimulus (any type of exercise that requires physical demand from the body). Those who are deconditioned or new to the activity should start with 2 to 3 sessions per week and slowly progress when they’re ready. When the activity starts to become easy and less challenging, that is when people should be progressing to the next highest intensity. 

As for the duration, 45 to 60 minutes is recommended. If you’re a beginner it’s best to start off with 30 minutes and then progressively increase (Attia & Attia, 2022). It’s essential to find a dose that is effective for your requirements. For example, someone with Type II diabetes will need longer durations per session than the average person. The dosage is also dependent on your current fitness level, specific training goals (Ex: maintaining or endurance based), and how much time availability you have on a given day. Zone 2 training can be very time intensive, so it’s important to plan ahead and incorporate a program that is most suitable to fit your needs and schedule (Attia & Attia, 2022). 

Ultimately, it is always recommended that you get clearance and approval from your doctor or primary care provider before starting a new exercise program to ensure that it is safe for you.

In conclusion, Zone 2 cardiovascular training has a wide array of benefits for anyone looking to develop their overall fitness and cardiovascular health. People can efficiently increase their aerobic capacity, optimize endurance, and stimulate fat breakdown by exercising at a moderate intensity within this heart rate zone. It will allow individuals to exercise for extended periods of time without being over exhausted and risking injury which can be a useful resource for all ages, fitness levels and training goals. 

Integrating Zone 2 cardiovascular exercise in your routine may help you achieve your fitness goals and enhance the quality of your life, regardless of whether you’re an experienced athlete or just starting out. So why not give it a try and see how it can benefit you?