Runner jogging under the bridge by the rivervgajic/Getty Images
On a recent run on Toronto’s waterfront trail, I sped past a friend of mine.
She told me, half-jokingly, that I only passed her because she was purposely running slowly to stay in Zone 2.
My friend is one of many runners and exercisers who are responding to the hype around Zone 2 training. Once a niche term buried inside exercise science textbooks, it has recently become a pop physiology buzzword, proselytized by world cycling champion Tadej Pogacar, public intellectuals such as Peter Attia and Andrew Huberman, and Hollywood leading men including Hugh Jackman and Chris Hemsworth.
Zone 2 is the most popular of the five heart rate zones, established over the years by exercise physiologists such as Sally Edwards, Joe Friel and Phil Maffetone, that are used as a shorthand method to gauge the intensity of a workout – and what combination of carbs, protein and fats your body is burning as fuel in the process.
You are in Zone 1 during a brisk walk, when your heart beats at roughly half of its maximum speed, and in Zone 5 near the end of a full-effort, 90-second run. You fall in Zone 2 when your heart rate is beating at 60 to 70 per cent of its maximum. (The general formula for determining your max heart rate is 220 minus your age.) It is the domain of an activity, such as an easy run or an honest bike ride, where you can hold a conversation, but not without taking a breath between most sentences. One can typically stay in Zone 2 for an hour or more without red lining, because the effort is not intense enough for your muscles to accumulate lactate and produce that burning sensation that comes at the end of an exhausting hockey shift or during a hard five-kilometre run.
This less-than-intense way of exercising is not new. Distance runners have for years made what’s known as “long slow distance” work part of their training, and clinician and author Maffetone wrote in 1996 about the importance of training at Zone 2, which he called a “fat burning zone,” to improve aerobic fitness.
But the practice is gaining steam as research finds that it’s a tremendous physiological bang for your buck. Athletically, it multiplies mitochondria, which are key for energy production, and it improves oxygen delivery to the muscles, building your aerobic base and laying the groundwork for substantial fitness gains.
Beyond that, Zone 2 training has been linked to reduced blood pressure and improved insulin sensitivity, and could potentially even stave off metabolic problems, which are strong predictors of heart disease and Alzheimer’s. And you get all of that without the higher risk of tearing a hamstring or blowing out your ACL that comes with intense exercise.
The biggest threat of Zone 2 training is simply doing too much of it – or, more precisely, letting it hijack your routine and choosing it at the expense of other things. The friend I encountered on the waterfront had started doing all of her runs at Zone 2, refusing to ever reach a heart rate higher than 127 beats a minute and ditching her previous exercise method – high-intensity interval training – in the process.
She had begun to think that Zone 2 simply means leisurely training. But by slowing down on all of her runs, she was leaving benefits of other kinds of training at the door. That’s a mistake: HIIT training comes with its own long list of health advantages. A 2024 study from Norway, for example, shows that intense exercise has even greater benefits to mitochondrial development than more leisurely workouts.
Experts agree that varying intensities of exercise is a good approach. Between staggeringly fast sessions, world-beating Kenyan distance runners do their easy runs very slowly. Pogacar, the world champion cyclist, does 80 per cent of his exercise at Zone 2.
When Trent Stellingwerff, a Victoria-based sport physiologist, coaches someone to run a 10-kilometre race, he aims for 75 to 80 per cent of their training to be at around Zone 2, and then the rest at a more intense pace.
“The value of Zone 2 is that you can get a decent stimulus over time, and as long as the athlete eats and recovers well they can bounce right out of these sessions very easily,” said Stellingwerff, who works with elite track and field athletes.
Sometimes he uses a qualitative measure called rate of perceived exertion (RPE) to gauge intensity, having an athlete rate their effort level out of 10. Zone 2 then becomes a three or four out of 10. The approach removes the risk of gleaning heart rate data from smart watches, which Stellingwerff says tend to not be as accurate as a chest strap or legitimate max heart rate tests in a lab.
Most people can benefit from fitting some Zone 2 training into their routine, especially because many common workout classes fall outside of its boundaries. Spin classes and boot camps aim to make you work much harder, whereas yoga and Pilates will rarely push you beyond Zone 1.
A regular dose of Zone 2 workouts may also protect against the common beginner mistake of going too hard all the time, and not grasping the benefits of going easy. Besides, a good balance of easy and hard shields you against the monotony of light work – and the terror of punishing HIIT workouts.
When I’m in doubt about my training in the middle of a run, I revert back to a timeless sentiment popularized by famed track and field coach (and Nike co-founder) Bill Bowerman: Make your easy days easy, and your hard days hard.
