No pain, no gain, right?

Well, maybe not.

There’s a new buzz with researchers when it comes to fitness approaches and it’s debunking the reigning king of cardio.

HIIT, high-intensity interval training, is on the hit list.

Ready to step into the spotlight is its gentler, kinder cousin, Zone 2 training. 

What’s up with that?

HIIT has been the go-to for many a fitness year. HIIT is when you do short bursts of extremely high-intensity activity for a short amount of time, ranging from 15 seconds to 4 minutes. You then take a quick break, then start another round of high-intensity activity, until you complete several cycles.1 

There’s no doubt that HIIT can quickly whip you into shape. You’ll burn a lot of calories, and you’ll keep on burning calories after your workout. You’ll gain muscle and endurance. Given all those advantages, why would researchers and fitness experts be tossing up questions about HIIT?

As it turns out, HIIT comes with some risks. 

First up? Injuries. Because of the intensity and repetition of HIIT, fitness coaches and doctors say they see an uptick in injuries. This is true for seasoned HIIT enthusiasts, but it’s also true for someone who’s just coming off the couch into new fitness goals and wants to achieve those goals quick. They’re likely to start out too hard with HIIT and injure themselves.

But there’s another new wrinkle with HIIT, one that researchers are watching with concern. There has been a growing body of research about the effects of chronic cortisol on the body. Cortisol is a stress hormone released in the body. Cortisol is something of a Goldilocks-kind of natural steroid, meaning that you don’t want too much or too little; you need it to be just right.

As it turns out, the amount of cortisol released during HIIT sessions can keep your body stressed to a level that could have diminishing returns on your overall health.2  Health reporter Maya Singh writes, “An increased amount of cortisol may really be a physiological cause of overtraining syndrome. Overtraining’s signs and symptoms include anxiety, mood swings, diminished strength when exercising, other signs of chronic fatigue, modifications in sleep habits, reduced immune function, and so on.”3 

So, not optimal.

What’s the solution?

That’s where some great news comes into play. Do you enjoy going for a brisk walk, one in which you feel like you’re getting to stretch your legs and get on a bit of a sweat, but one in which afterwards you feel energized and refreshed?

That would be Zone 2 cardio.

What about a nice long bike ride, where you chat with a friend while moving down the trail? You end your ride feeling invigorated.

Yep. Also Zone 2 cardio.

Zone 2 cardio is when you are in motion, doing an activity like walking or biking or swimming, but your exertion is kept at a pace so that you can talk. You set a pace that allows you to do the activity for a longer period of time, instead of going for failure like in HIIT.

Zone 2 isn’t leisurely; you are pushing yourself to a moderate intensity level. But it’s a sustainable level, one that doesn’t make your body think you’re trying to run away from a bear and therefore dumps more cortisol into your system to help facilitate that.

So, score one for Zone 2 when it comes to keeping spikes in your cortisol at bay.

Another point for Zone 2? A little thing called fat utilization. As it turns out, HIIT often relies on glycogen stores in your body to be able to keep the intensity high. With Zone 2, your body is more reliant on your fat stores for energy as you work out. The more Zone 2 you do, the better your body gets at fat utilization for energy. And over time, this means you could experience greater fat loss, all while doing a workout that feels far more enjoyable than the rigors of HIIT.

And then there’s this: Zone 2 really does help build your aerobic capacity. Sure, HIIT can leave you breathless and gasping, and that can feel like you’re building something along the lines of aerobic fitness. But over the long term, Zone 2 also has a profound effect on your oxygen exchange. The steady-state experience of Zone 2 helps you build endurance as well.

So why aren’t we all doing Zone 2 all the time?

Zone 2 does require more time than HIIT. After all, you can do an extreme HIIT workout in 20 minutes that will leave you gasping and soaked in sweat. With a Zone 2 workout, you’ll be walking longer, biking longer, swimming longer, though not as intensely. And it will likely take you a bit longer to see the results you’re after with Zone 2. But over the long haul, Zone 2 is more sustainable and can stay with you as you age. Zone 2 functionally keeps you toned and ready for long days hiking or going with your kids to the amusement park.

And when it comes to keeping your stress markers down, Zone 2 wins hands down.

Ready to get your own Zone 2 workout on?

Check out this Zone 2 calculator which can help you determine what heart rate you want to maintain as part of your Zone 2 training. Zone 2 is when you exercise at 60%-70% of your maximum heart rate. Your maximum heart rate is determined by your age. You can track how you’re doing on your wearable device. And for bonus points, if you’re an Altrua HealthShare Member on certain memberships, you can keep track of your progress on the Altrua HealthShare App. (If you’re not sure if your Altrua HealthShare membership includes access to the Altrua HealthShare App, or you’d like to learn more about becoming an Altrua HealthShare Member, contact your Member Services Representative at 1.866.986.4506).

If you still want to keep HIIT as part of your repertoire, you can do that. Consider doing one HIIT workout a week and balancing it with plenty of Zone 2 cardio. It could be just the right recipe for you!

1. https://health.ucdavis.edu/blog/cultivating-health/high-intensity-workouts-can-help-you-get-fit-fast-but-preparation-is-key/2022/09
2. https://www.healthline.com/health/fitness/the-cortisol-creep#What-is-HIIT?
3. https://www.ndtv.com/health/what-is-cortisol-creep-can-hiit-workouts-stress-you-out-3382442#:~:text=An%20increased%20amount%20of%20cortisol%20may%20really%20be%20a%20physiological%20cause%20of%20overtraining%20syndrome.%20Overtraining%27s%20signs%20and%20symptoms%20include%20anxiety%2C%20mood%20swings%2C%20diminished%20strength%20when%20exercising%2C%20other%20signs%20of%20chronic%20fatigue%2C%20modifications%20in%20sleep%20habits%2C%20reduced%20immune%20function%2C%20and%20so%20on.