If you think effective cardio training requires fast-paced, all-out bursts of hard effort that leave you panting, sweaty, and sore, we’ve got news for you: Dialing back your intensity — at least some of the time — via zone 2 training can notably improve your overall performance and health.
A consistent regimen of slow-paced, low-intensity cardio, along the lines of an easy jog or relaxed bike ride, has been shown to improve endurance, heart health, and even insulin sensitivity.
In other words, taking it easy — or, at least, easier — a few hours each week is a worthwhile investment in your long-term fitness.
The Science of Zone 2
Just how easy are we talking? Zone 2 sits in the comfortable space between easy and hard: It’s a low- to moderate-intensity level of 60 to 70 percent of your maximum heart rate.
Heart-rate training is based on five zones, or thresholds, that correspond to how many beats per minute your heart is pumping relative to its maximum capacity, explains Life Time dynamic personal training director Jeff Rosga, NASM-CPT, NASM-PES, CES, BCS.
In zone 1, your heart is pumping at a minimal percentage of its capacity; this would be a warm-up pace that can be maintained for a long period of time. On the other end of the spectrum is zone 5, which maxes out your heart rate and is a very high intensity that can only be sustained for a short period.
“Zone 2 is considered aerobic,” says Rosga, meaning your body relies mainly on fats, carbohydrates, and oxygen for fuel. This is the level of training during which the heart is able to deliver plenty of oxygenated blood to the muscles.
At this intensity, your cardiovascular system is benefitting from several notable adaptations, says integrative cardiologist Mimi Guarneri, MD, author of The Heart Speaks. Zone 2 training strengthens your heart muscle. And the more you train at this intensity, she says, the more efficient your body will become at using oxygen during exercise, a measurement known as aerobic capacity.
Greater aerobic capacity, also known as VO2 max, is associated with a wide range of benefits, from improved heart health and blood-sugar regulation to greater longevity.
Additionally, increasing your aerobic capacity improves cellular function, which boosts the flow of oxygenated blood to your muscle tissues, prompting your muscles to make more and larger mitochondria. The powerhouses of cells, mitochondria are organelles that use oxygen to create adenosine triphosphate, which is the fuel that makes your muscles contract.
The more mitochondria you have, the more oxygen you’ll be able to use. This gives your cells a robust and stable energy supply, boosting stamina and warding off fatigue.
“You’ll be able to go farther or longer — or both — without tiring,” explains Life Time master trainer and nutrition coach Lindsay Ogden, CPT.
Beyond Endurance
Though improving endurance is a major benefit of zone 2 training, it’s not the only one. The lower intensity reduces strains on your connective tissues and nervous system, making overexercising less likely, says Rosga. It can also help you recover by decreasing your body’s fight-or-flight responses, improving resting heart rate, and enhancing blood flow.
This type of training is also associated with numerous general health markers and longevity, especially when included in a routine that incorporates strength training.
“Zone 2 exercise decreases blood pressure and triglyceride levels and improves mental well-being,” says Guarneri. Moreover, she explains, zone 2 training enhances glucose regulation and insulin sensitivity because the increased number of mitochondria supports the body’s ability to process glucose and regulate blood sugar.
Finally, notes Ogden, zone 2 training is scalable to the individual and easy to do consistently. “It’s sustainable.”
Do these benefits mean you should abandon your high-intensity interval training (HIIT)? Not at all, says Rosga. If you want to improve your performance, strength, and conditioning, it’s not a matter of either-or — it’s both.
“It’s important to realize that both longer, low-intensity [zone 2] cardio and HIIT help develop your energy systems in different ways,” explains Joel Jamieson, CSCS, a go-to trainer for Navy SEALs and pro athletes. “There shouldn’t be a debate about which one is better — they lead to different adaptations, and each has unique benefits.”
Your Zone 2 Training Plan
Find your zone.
Figuring out what your zone 2 effort feels like is essential. The activity and pace required for you to reach zone 2 depends on your fitness level and the types of exercise you regularly do.
“An elite runner may be in zone 2 while jogging a nine-minute mile, whereas the same exercise and pace could place someone who only lifts weights in zone 3 or 4,” Ogden says.
The most accurate way to determine and track your zone is by taking a cardio test known as an Active Metabolic Assessment (AMA) and then using a heart-rate monitor (preferably with a chest strap) during your training. (Learn more about AMA testing at “The Active Metabolic Assessment: The Most Accurate Test For Cardio Training.”)
There’s also a simple and reliable low-tech approach: Check in with your breathing. You’ll know you’re in zone 2 during exercise if you can breathe comfortably through your nose only, or if you can speak aloud without getting breathless. (If you’re training alone, try to speak a few words out loud to test your breathing; if you’re working out with a buddy, you’ll be able to maintain a light conversation in zone 2.)
If nasal breathing becomes heavy and uncomfortable, or you need to switch to mouth breathing, you’re creeping into zone 3.
Set your schedule.
To achieve the effects of zone 2 training, building up training volume is key. That’s because “longer, slower training helps develop the capillary network that is responsible for delivering the oxygen supplied by the heart to the working muscles,” explains Jamieson. “It takes a higher volume than you’re likely to do with HIIT for this to happen.”
Rosga recommends at least 150 minutes per week of moderate-intensity activity (zones 1–3). A good rule of thumb is 40 to 60 minutes of zone 2 training at a stretch, aiming for two to four hours per week. (Exercise newbies are encouraged to start with shorter zone 2 sessions and gradually build up their volume over time.)
To balance zone 2 training with HIIT training, Rosga advises spacing out your days of high-intensity work throughout the week and targeting 75 minutes per week of vigorous activity (zones 3–5). For those individuals looking for the right balance in their cardiovascular fitness plan, Rosga recommends using the 80/20 rule: 80 percent of your weekly time should fall in the lower intensity zones and 20 percent of your time should focus on high-intensity work.
And, Guarneri notes, don’t forget to include resistance training in your weekly training mix. “Building muscle is a key ingredient for longevity,” she says.
Choose your exercises.
You can use many exercise modalities for zone 2 training, but cardio options like walking, cycling, rowing, swimming, hiking, and jogging are likely your best bets.
“To get the maximum benefits, you want to stay in zone 2 without much change in effort or speed,” Ogden says. Though resistance training and mind–body practices like yoga are vital components of a well-rounded exercise program, they don’t allow you to maintain your intensity long enough to reap the benefits of zone 2 training, she adds.
Track your progress.
A lower resting heart rate and improved heart-rate variability are indicators that your cardio endurance is improving. You might notice that you can maintain your zone 2 effort for a longer distance or duration. Or you’ll find that you can do a harder activity (say, jogging instead of walking) without spiking your heart rate.
This article originally appeared “Low, Slow Cardio” in the September/October issue of Experience Life.
