Zone 2 Cardio - The Most Important Exercise For Heart Health
The heart is the most important muscle in the body. Without it, nothing works – you're dead! Unfortunately, every year the number one killer of Americans is heart disease. In 2020, more than half a million people died from this ailment.
Since all bodily systems depend on the heart, if we can make it more efficient it will improve all aspects of health. As someone who has been weightlifting for over 20 years, I believed that this was enough to stimulate my cardiovascular system. While weight training can help to thicken the heart and allow it to contract more vigorously, it does not build the level of efficiency that pure cardiovascular exercise does.
Cardiovascular training can be delineated based off their intensities, which are commonly divided amongst Zones 1 through 5. Zone 1 being the easiest, think gentle walk, and Zone 5 being the most intense, think an all out sprint. Overall, Zone 2 cardiovascular training is the best form of cardio that you can be doing. This lower intensity steady state cardio will build your aerobic base and will give you benefits when you perform your higher intensity exercises. Even the most elite athletes spend around 80% of their training in Zone 2 because of its many crossover benefits in the higher Zones.
In this article, I will explain what occurs in the five different training zones, why you should do the majority of your cardio in Zone 2, and the many benefits that come from adding it to your lifestyle.
Zone 2 is moderately paced cardio with an intensity low enough that you can carry on a conversation while doing it. If you were conversing with someone, they would know you are working out, but you won't be gasping or having to pause for a breath.
Physiologically, Zone 2 can loosely be described as 65-70% of max heart rate, or around 120-140 beats per minute (BPM). You are working at an intensity level where the body is bumping against your aerobic threshold without going into the anaerobic energy systems. Your aerobic threshold is also know as your ventilatory threshold or VT1. Your first ventilatory threshold is when lactate, a byproduct of anaerobic energy systems, starts to accumulate in your blood faster than it can be cleared. Another way to think about this is that lactate is a byproduct of glucose utilization. If lactate is being produced, then you know you are utilizing glucose as a fuel instead of fat. The body attempting to buffer this lactate will cause your breathing rate to increase and become more labored. The increase in labored breathing is a huge indication you are hitting and going beyond your VT1 and have moved out of your Zone 2 level. As a side note, all the energy systems are happening simultaneously, but one system will be more prominent depending on your intensity level.
The Talking Test
Simply put, you know you are doing Zone 2 cardio if you can speak a 12 word sentence in one breath or you can comfortably recite your ABC's. If you cannot, you are more than likely in a higher heart rate zone.
The Zones
Zone 1 is a gentle walk. You aren't sweating or forcing any bodily adaption. It is easy to talk and heart rate is barely elevated from resting heart rate.
Zone 2 is an endlessly sustainable period. It is where max fat oxidation is occurring. The body is utilizing fat for fuel with relatively low amounts of glucose. You are able to carry on a conversation – remember the talking test. You are increasing adaptation without orthopedic or metabolic stress, therefore you aren't accumulating carbon dioxide, lactate or other metabolites in your blood. You aren't beating up the body and you'll be ready for another bout the next day.
Zone 3 is like running a 5k at your hardest sustainable level. Zone 3 is an in-between zone where you are still using fat as fuel, but you have switched over into glycolytic systems and started utilizing glucose as a fuel source. Metabolites are beginning to accumulate in your blood. This is where VT1 starts to kick in. This zone is a grey zone between the lower and higher intensities, and more than likely where most people are training when they are going for a jog. It feels harder so people think they are getting a good workout, but that feeling doesn't translate to the best adaptation for your cardiovascular system.
Zone 4 is running a mile as hard as you can. The body is producing lots of metabolites. You are burning through energy and oxygen faster than you can replenish. Breathing is labored. This is where your high intensity interval training (HIIT) is occurring.
Zone 5 is maximum effort and can only be sustained for a short time. Lactic acid will build up quickly and your muscles will burn. This is an all out sprint.
Benefits of Zone 2
Improves cardiovascular health
There are four chambers of the heart, and the left ventricle is the thickest chamber. It is responsible for pumping oxygenated blood to tissues through the entire body. Zone 2 training will allow maximal blood to saturate the left ventricle. Over time, this will “stretch” and increase the size of your left ventricle. Therefore, more blood will be pumped per heartbeat. Since more blood is pumped per beat, the heart doesn't have to work as hard and will become more efficient. This singular benefit helps to explain why doing lower intensity allows your body to better adapt at all other intensity levels.
Increases the number and efficiency of mitochondria in your body.
The mitochondria are the powerhouse of the cell and they create the energy your body needs for activity. The more mitochondria you have, the more ATP you can produce; thus the more energy output you have.
Zone 2 makes your mitochondria more efficient at utilizing fat as an energy source. As your body can store more fat than carbohydrates, you will basically have an endless supply of energy for low intensity steady state cardio.
People who are metabolically unhealthy will bypass utilizing fat as an energy source and go straight to glucose for fuel. Their bodies do not know how to utilize fat and are strictly carb burners. Zone 2 helps to make the mitochondria healthy again in utilizing fat as a fuel source during lower intensity exercise.
Increase work capacity
Since you will be able to replenish your ATP in a shorter amount of time, you will recover more quickly and you will be able to do more work volume in the same amount of time. If you are weight lifting, this will mean less rest between sets. If you are rolling in jiu jitsu, this will mean less rest needed between matches. If you are planting multiple trees in your yard, you'll be able to dig a hole and recover more quickly to dig the next hole.
Zone 2 Doesn't Beat Up Your Body
If you are training hard, then you need to give your body time to recover. As mentioned before, Zone 2 doesn't cause metabolites or waste products to accumulate in your blood, nor is it taxing your muscular system. Because of this, you can perform Zone 2 multiple times per week without it negatively effecting your other training.
Performing Zone 2
You should aim for four to five sets of 30 minute sessions per week. If you can make those sessions 45 minutes, even better. The sweet spot is around 150 minutes of Zone 2 per week, while coupling it with 20-30 minutes of Zone 4. This will give you a well-rounded cardiovascular system – ready for long, sustained bouts or quick, explosive sprints.
Perform Zone 2 in a controlled environment so that you can easily regulate your heart rate, and utilize a device that gives you watts or RPMs so you can track your progress over time.
I personally enjoy doing my Zone 2 on an Assault fan bike. I get my arms and legs involved and I can easily listen to a podcast or watch a video. It also has the benefit of giving me watts and RPMs. After every session, I take a picture of the screen on my smart phone for easy record keeping.
If you have access to one, utilize a heart rate monitor for increased accuracy or simply use the talking test.
Trying to maximize your time? Take the talking test one step further – try to have a phone conversation with someone. The person on the other line will know you are exercising, but you should be able to comfortably talk. It is a self-regulating activity. If you are gasping for air, lower your intensity.
Conclusion
I used to think that going harder was the answer to improving my heart, but thanks to science, we now know that easy, lower intensity steady state cardio will give the body more benefits and will improve all other intensity levels.
As a personal trainer and someone who practices jiu jitsu, I discovered that I would gas out way earlier than my opponents. My ego was frustrated that my years of working out were not expressing themselves towards performance on the mats. I have never been a runner, nor did I do any specific cardiovascular training. I believed my kettlebell workouts would suffice, but I was missing something from the health equation.
To solve this dilemma, Zone 2 training came into my life. The results have completely surprised me with my resting heart rate going down 10 beats per minute, my blood pressure normalizing, and my endurance increasing while my recovery time decreases.
Overall, Zone 2 training shows that we can get many health benefits without beating up the body. Zone 2 will improve your heart health and make your cardiovascular system more efficient. It will allow you to recover more quickly and enable you to do more. Life becomes easier when moving isn't as labored. In the end when your heart works better, you work better.
To your health,
Trey
Deeper Dive
I highly recommend these podcasts with Jordan Syatt and Alex Viada
The Science of Zone 2 Cardio with Alex Viada (Part 1)
The Science of Zone 2 Cardio with Alex Viada (Part 2)
And this talk with Iñigo San-Millán, Ph.D. & Peter Attia, M.D.
Deep dive back into Zone 2 Training