Zone 2 – Is it all you need to do?
This week I am focusing on one article, as I have seen quite a bit of discussion about it online recently. A new research article was released in the journal of Sports Medicine on June 25th (fresh off the press!) reviewing the benefits of zone 2 training.
First, I have to congratulate the authors not only for selecting the title “Much Ado about Zone 2”, but also because this article represents a great summary of what we know and don’t know about the benefits of zone 2 training (1). So, let’s dive in!
What is zone 2 training, again?
Zone 2 training essentially boils down to exercise at a low, steady pace. This is exercise that occurs below your lactate threshold (feel free to go back to episode 6 for a refresher on the lactate threshold). This type of exercise feels like work, but a sustainable level, something you could do for hours on end.
Why are we talking about zone 2?
Recently, particularly through popular social media influencers and podcasters, zone 2 exercise has been lauded for its benefits, with some suggesting that it is the optimal way to train. Proponents argue that you may not need to exercise above this level, because if you want to optimize your health, then zone 2 is the way to go.
Doctor’s note: Any time somebody claims they know the optimal or best version of anything, I recommend proceeding with caution. This includes the best diet, supplements, exercise regimen, etc. Science isn’t in the business of making absolute claims about what is best in all cases. Instead, it helps us understand what tends to work better under certain conditions, based on current evidence. Current research is often provisional and remains open to revision as new data emerges.
Okay- so where did the hype for zone 2 come from? Well, it’s no secret that most high-level endurance athletes will spend a significant amount of their training in zone 2. And when comparing high-level athletes with the general population, we see improved cardiorespiratory function and improved mitochondrial health and function. However, correlation should not be confused with causation, and there are a few reasons we should be skeptical about causation here.
High-level athletes are not a great barometer for many of us, as they may spend 20 or more hours per week training. Meanwhile, for the general population, the American Heart Association recommends getting over 2.5 hours of moderate-high intensity exercise per week—a much smaller number. Because these athletes are spending so much time exercising, they need to make a significant amount of their exercise lower intensity. It keeps them active but will not cause undue stress on their body or increase their injury risk as much as 20 hours of sprinting-as-fast-as-possible could. Nevertheless, these athletes will spend time at higher intensities and reap the benefits of multiple different types of exercise intensities (2).
Think of it this way: If that high intensity athlete who trains 20 hours a week spent 5 hours doing high intensity (above zone 2) training (achieving 200% of the American Heart Association’s minimum suggestion), they would still be spending 75% of their time in zone 2 or below! Because of this zone 2 will always be a majority of their training, but that doesn’t necessarily mean that is where a majority of the benefits are made.
So, what is the takeaway?
The paper goes on to take a closer look at some specific claims, related to mitochondrial capacity, gene expression and cellular signaling, fatty acid oxidation, and even cardiorespiratory fitness. The authors reference studies showing some benefits, yet there are other studies showing inferiority of zone 2 when compared to higher intensity exercise.
In effect, at this point in time, there is insufficient data to say that zone 2 training is the optimal type of training. And in my opinion, claims like this start to miss the point. The answer to ‘what is the most optimal’ will always be nuanced. It depends on your goals, your health, your current status/function, and many other factors that we are only beginning to understand. Because of that, the optimal training for me likely looks different than the optimal training for you.
But it isn’t just about that either. Exercise is an integral part of our health and our wellness, but it’s also a way to relax and unwind, to meet with friends and socialize. At the end of the day, variety is often the best solution. Getting a mix of low intensity exercise, high intensity exercise, and strength training is going to keep you healthy and support your body in a myriad of ways. But most importantly, do what is fun and exciting for you! Whatever keeps you active is the optimal place to start.
Sources and Further Readings:
Much Ado About Zone 2: A Narrative Review Assessing the Efficacy of Zone 2 Training for Improving Mitochondrial Capacity and Cardiorespiratory Fitness in the General Population | Sports Medicine [Internet]. [cited 2025 Jul 2]. Available from: https://link.springer.com/article/10.1007/s40279-025-02261-y
Casado A, González-Mohíno F, González-Ravé JM, Foster C. Training Periodization, Methods, Intensity Distribution, and Volume in Highly Trained and Elite Distance Runners: A Systematic Review. Int J Sports Physiol Perform. 2022 Apr 13;17(6):820–33.
