Heart rate zones are used to guide exercise intensity during an aerobic workout, with Zone 1 an easy pace and Zone 5 maximum effort. But, lately, everyone’s talking about Zone 2, a moderate intensity workout that fitness influencers believe is the key to health, fitness and longevity.
Adding to its popularity is the fact some of the world’s best endurance athletes claim 80 per cent of their training is spent in Zone 2. That’s surprising given performance is generally thought to be optimized at higher intensities. But with such high training volumes, elite runners, swimmers and cyclists need to preserve energy in their working muscles, which is why they’re strategic about how much of their weekly training is done above Zone 2.
For recreational athletes, the buzz around Zone 2 training isn’t as much about its potential to manage training loads, but rather its ability to increase the number, size and efficiency of the mitochondria. Often referred to as the powerhouse of the cell, the more mitochondria you have the greater the amount of energy you’ll be able to tap into when working out. And since a loss of mitochondria is linked to aging and age-related diseases, increasing their numbers is thought to boost longevity.
What kind of intensity are we talking about when it comes to Zone 2 training?
There are several ways to determine exercise intensity, but one of the simplest is heart rate, with maximum heart rate (determined by subtracting your age from 220) considered peak intensity. In a five-zone model, exercising in Zone 2 means requiring an effort equivalent to 60-70 per cent of max heart rate. It should feel slightly above a cruising pace, but sustainable for the full workout. You should also be able to talk during the workout, albeit not comfortably.
Yet despite the suggestion the bulk of your workouts should be done in Zone 2, not everyone is sold on its promise of improved health and performance, especially for recreational athletes.
Brendon Gurd, a professor in the School of Kinesiology and Health Studies at Queen’s University, has spent 20 years studying how exercise affects the mitochondria. As the primary author of an article called Much Ado About Zone 2, published in Sports Medicine, he claims the advantages of Zone 2 training for recreational athletes are overstated.
“We challenge the broad endorsement of Zone 2 training for members of the general public, as it contradicts substantial evidence supporting the use of high-intensity exercise for improving mitochondrial capacity and cardiometabolic health,” said the Gurd and his co-authors who hail from the universities of Queens and McMaster.
To be clear, Gurd and his colleagues aren’t against Zone 2 training, they just question the suggestion by health and fitness influencers it should be prioritized over other forms of training.
“The advocacy for Zone 2 exercise over higher exercise intensities to improve mitochondrial capacity, and health, also contradicts experimental evidence and physical activity recommendations in exercise science,” the team of exercise scientists says.
Indeed, it’s long been held a body needs to be pushed beyond its limits to spark the adaptations needed to improve fitness and performance. For some individuals, Zone 2 training may be enough stress to initiate the desired physiological responses to improve fitness and mitochondrial efficiency. But for any veteran runner, swimmer or cyclist, exercising at a moderate intensity isn’t challenging enough to overload the working muscles.
Gurd warns recreational athletes shouldn’t automatically assume what works for the world’s best athletes will work for someone whose training is squeezed between work and family commitments. Even with the majority of their training spent in Zone 2, elite athletes still spend plenty of time cranking up the pace into the highest two zones.
“It may be that the high mitochondrial capacity of elite endurance athletes is more related to their training spent above Zone 2 rather than their large volumes of Zone 2 training per se,” Gurd and his co-authors said.
The fact is, the more well-trained the exerciser, the more important it is for the body to be challenged by high intensity workouts. And while there is no conclusive breakdown as to the perfect balance between high intensity exercise and Zone 2 training, keep in mind changes to mitochondria and fat oxidation are optimized at high not moderate intensities.
“Zone 2 may fall below the moderate-to-vigorous intensity range recommended by physical activity guidelines and, thus, advising the general public to forgo higher exercise intensities in place of Zone 2 may limit the health benefits of exercise,” Gurd and his colleagues said.
Where does that leave you when it comes to choosing which intensity to train? The most effective training programs alternate between hard, easy and moderate workouts, with the right ratio between the three based on your own personal goals. So while spending a lot of time in Zone 2 builds a good aerobic base, like many of the fitness programs touted on social media its promises don’t always match the hype.
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