Zone 2: Are we even talking about the same zones?

Zone 2 training has become quite the buzz term over the past few years. But it is with good reason. There are significnat health and performance benefits that come with spending significnat time in "Zone 2". 

But there can be some confusion surrounding this all importnat zone. It comes from the presence of multiple systems of zone classification. The three most utilized systems are the 3, 5, and 7 Zone systems. 

As previously stated, there are many benefits to Zone 2 training. But regardless of what system you use, this type of training is always performed below your aerobic threshold, meaning that aerobic metabolism is the primary source of enegy production. This simply means that energy is being produced in the presence of adequate oxygen. 

These benefits include: [1]

• Increase in the number of mitochondria
• Increase in mitochondrial efficiency
• Increase in “metabolic flexibility” - (utilizing fat for fuel)
• Lower resting heart rate
• A decrease in blood pressure
• Lower risk of injury
• Improves insulin resistance
• Improve your ability to run/cycle longer
• Improve your resilience and ability to deal with increasing load
• Improve your Zone 4,5 function/performance

As you will see, Zone 2 training does not apply if you are using a 3 zone system to describe your training, as Zone 2 will actually describe your threshold zone. 

(A typical 3 Zone System which shows the Aerobic Threshold (LT1) between zones 1 and 2)

But when you start using a 5 or 7 zone system to program your training or discuss running, Zones 1 and 2 are performed below Aerobic Threshold. 

(A 5 Zone System shoes that Zones 1 and 2 fall below LT1/VT1)

(A breakdown of a 7 Zone System which has Zones 1 and 2 below Aerobic Threshold)

The reason for the different systems is that the more zones allow for more specificity in determining the goal of your training. 7 zone systems are typically reserved for higher level performers, while 5 is typically a good mix of detail and generality which can help runners focus on charateristic of their training without getting bogged down by looking at your watch too much while training. 

----------------------------------------

Prior to running my first marathon, I just thought that I need to try and run for long distances and just try to run faster and faster. And honestly, this got me pretty far. However, I wanted to be better than I was. 

I began researching, hired a coach, and realized I was not recovering well because I was always trying to run too fast.

This whole “mitochondrial density” is not just some science mumbo jumbo either. Zone 2 running allows yours cells to utilize energy more efficiently, and having more mitochondria allows you to more easily convert stored energy into usable energy. 

So next time you just want to let it all out on your next scheduled slow run, remember that you’ll be missing out on all the benefits above!

PS: if you don’t know what your “zone 2” HR is or have a way to measure it, conversational pace has been shown to be a great indicator of being in Zone 2. [2]

1. Mujika, I. (2021). Endurance training: Science and practice (2nd ed.). Human Kinetics. 2. Quinn, T. J., & Coons, B. A. (2011).

2. The Talk Test and its relationship with the ventilatory and lactate thresholds. Journal of Sports Sciences, 29(11), 1175–1182. https://doi.org/10.1080/02640414.2011.585165