by Tim Curry, MS ACSM-RCEP

Zone 2

What do you think the most underutilized training zone by many endurance athletes is? Perhaps Zone 5 with its maximal, “I am going to puke” efforts or Zone 1 with intensity so low it could be accomplished with an extended brisk walk? Surprisingly, Zone 2 is consistently neglected, often to the detriment of the athlete. Let’s take a look at what Zone 2 training is, how it impacts fitness, and why it matters to your performance.

The Powerhouse of the Cell

Pop quiz: what is the powerhouse of the cell?  The mitochondria of course! You likely recall this from high school biology class, but very few people know why this organelle is so important to our athletic performance. 

Mitochondria are where aerobic (meaning ‘with oxygen’) metabolism occurs in the cell. Think of it as the oxygen-using engine that many, but not all, of our cells rely on for production of the fuel they need to do…well, everything! This engine can metabolize, or break down, both fats and carbohydrates (and if absolutely necessary protein), into ATP which is the energy currency of our cells. Aerobic metabolism is where we create the lion's share of the ATP our body needs to survive and thrive! It allows us to do our daily activities, and the sports we love, therefore it’s no surprise that the development of this area of the cell is quite important for many reasons. This leads us right into Zone 2 training. 

The Fat-focused Zone 

Zone 2 training is all about improving the density and size of our cell’s mitochondria by creating an environment that forces the cells to perform large amounts of aerobic metabolism. Cells are only able to metabolize fat aerobically, so we use Zone 2 work to help our cells maximize the rate of fat usage during activity. Maximizing our cells' fat usage through increased aerobic demands gives them a longer-lasting fuel source. The cells adapt by creating more mitochondria and expanding the size of the ones they have, both of which increase the ability to perform aerobic metabolism and improve aerobic capacity. 

What do these larger and more numerous mitochondria mean for athletic performance? Simply put, you can utilize more oxygen for aerobic metabolism! This has numerous benefits such as being able to utilize fat as a fuel source up to higher power outputs. More importantly, you’ll also be able to produce more ATP aerobically. This means your cells are more effective at clearing out the metabolic byproducts during hard efforts that hinder our cells’ functioning while riding. Your body will also be better at using lactate (which is metabolized aerobically) as a fuel, especially during points where we are building up large amounts of it. Finally, improved aerobic fitness is a major risk reducer for many chronic diseases long-term, and while not training-related, it’s still important for health! There are numerous other benefits that fill scientific and academic papers but let’s switch gears and explore how to perform this training.

Low, slow, and a bit boring

The best way to set Zone 2 is by using the data from a lactate threshold and VO2max test to identify the area of maximum fat usage in grams per minute. This is then used to set the upper and lower heart rate and power zones for Zone 2. Unfortunately, unless you have a lab with a gas analysis machine (or $20,000 to buy your own), plus time to attend courses on exercise physiology to learn how to use it, you might find yourself searching for other options. 

Thankfully, there are two free tools we can use to set our Zone 2: Rating of Perceived Exertion (RPE) and the Talk Test (TT). Zone 2 is generally a 2-3 out of 10, meaning it feels ‘very easy’ to ‘easy’ on the RPE scale. For the TT a good approach is to imagine you’re on a phone call with your peers for a project. While on the call, would your peers know that you were active in some way but you could easily be a productive team member while working on a complex project? That’s around where you want to be, but if you feel like you’d start to lose track of the conversation compared to just sitting in a chair then you’re going too hard. 

For those of you who have a heart rate monitor and don’t mind a little bit of math, zone 2 can be prescribed a few ways. On the easiest end of the spectrum, it can be calculated as 57-64% of heart rate maximum. To add a little bit more complexity it’s 30-40% of heart rate reserve (HRR). For HRR we use the equation [(HRmax-HRmin) x training %] + HRrest. If you’ve performed a Functional Threshold Power (FTP) test recently (and are confident with the results), you can use 68-80% of your heart rate at FTP. Regardless of the way you calculate your zone heart rate make sure to use RPE and/or the TT to check that you are not going too hard while riding. Zone 2 training tends to feel a bit slow, unproductive and boring while you’re actually doing it. This is the reason many people fail to spend enough time in Zone 2, despite its importance to our performance (and health!). 

How Long and How Often?

For endurance sports Zone 2 riding is critical, so it makes up a large percentage of total training time. Scientific research supports the recommendation that around 70-80% of total training time be spent in Zone 2. This is a tremendous difference compared to what people actually do on their training rides so you’ll likely have to make adjustments and be deliberate about riding in this zone. This also means if you’re riding 5-6 days per week then 4-5 days should be spent solely in zone 2. This is a great guideline to get you going in the right direction and gain the benefits from this zone. Once you establish your fitness in this area it’s not unusual to see more Zone 2 days and time further out from race season and fewer closer to higher intensity races. Regardless, make sure that during your Zone 2 rides you stay in Zone 2 as much as possible. Remember that you are going low and slow to improve your performance! Resist the urge to go chase that person who just passed you!

Leveraging Your Mitochondria Superpowers

While Zone 2 is a critical area for training it is far from the only one. Cycling, just like any other sport, requires a range of efforts, and therefore a variety of training methods and zones. Up next, we'll discuss Zone 3!

To learn more about the concepts covered in this article while earning NICA CEUs, check out our recommended courses below!

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