Is all cardio exercise created equally? Most of us know that cardio does wonders for your heart and cardiovascular system. But is panting for air and doing sprints a necessity to max out the benefits—or are casual workouts good enough? And what’s the difference between aerobic and anaerobic cardio? The key to understanding the spectrum lies in the 5 distinct heart rate zones.
Depending on the intensity and duration of your cardio training, your body will tap into different energy sources and experience distinct benefits. Assessing which heart rate zone you’re training in can help you understand whether you’re doing aerobic or anaerobic training. Building that level of awareness can help you work out smarter—and more sustainably.
For a beginner-friendly guide to heart rate zones plus aerobic and anaerobic training, we turned to Melody D., a fitness expert, obé instructor, and obé’s Senior Manager of Programming.
Aerobic vs. Anaerobic Activity: What’s the Difference?
Both aerobic and anaerobic activities are beneficial for your cardiovascular system, boosting circulation, metabolism, and heart health. The differences come down to how you use stored energy plus the intensity and duration of the exercise.
Think of aerobic activity as endurance-based or “steady-state” cardio sustainable for long periods. Repeated, continuous movements like walking, swimming, running, hiking, and biking all fit the bill.
Aerobic translates to “with oxygen,” meaning that in this activity type, your body relies on oxygen as its main energy source for breaking down additional fuel and keeping you moving. As your muscles demand more oxygen, blood flow increases, and your heart rate climbs. This conditioning strengthens your lungs and heart, reduces mortality risk, aids mood, lowers blood pressure, activates the immune system, and more. It also uses slow-twitch muscle fibers to boost endurance.
Anaerobic activity—”without oxygen”—is sprint-based exercise that can only be sustained for short bursts of time. Running intervals, sprinting up a hill on your bike, or taking a HIIT class all fall into this category. While we’re focusing on cardio-based forms of anaerobic exercise, strength training also falls into this category.
Because you’re working at your highest level of effort, your body demands more oxygen than you can supply, which forces it to turn to energy stored in muscles for fuel. With lactate buildup, you won’t be able to keep it up for long—and that’s the goal! By engaging your fast-twitch muscle fibers to hit their max, you’ll build strength and muscle mass. This process also boosts your metabolism and expends more calories, which makes anaerobic exercise the best option for weight loss (if that’s one of your goals!).
Pro tip: Measuring your heart rate max or RPE
Everyone is different—and factors like genetics, physiology, and what medications you’re taking can all affect your max heart rate. But for a quick approximation, use this equation: 208 – (0.7 x your age). If you don’t have a heart rate monitor (or wearable) that can track your heart metrics, assessing your RPE (rate of perceived exertion), aka how hard you’re working, can also help you navigate the various heart rate zones.
⭐️If you have a wearable, you can reference your Health metrics on the Insights tab of the obé app to see your heart rate during class.
How Do Heart Rate Zones Fit In?
The 5 heart rate zones—ranges that correspond to training intensity—generally match the aerobic/anaerobic dichotomy. Understanding your effort level for each zone can help you tailor your training to your needs, making each workout safe and effective for your fitness level.
The training zone level you reach also depends on how you choose to show up to your workout. “I could take a Dance Cardio class and decide I’m going to push it and go big in my movements to get my heart rate up,” says Melody. “Or I could decide I need to chill and go for a low-impact option to scale back on my intensity. You can find different heart rate zones within the same class types which gives you a lot of flexibility.”
Heart Rate Zone 1: Aerobic Activity
What you’re doing: Going for a casual stroll or walk. Gardening, carrying groceries, housework. Anything in the NEAT (Non-Exercise Activity Thermogenesis—more on that here) living your life category. Warming up or cooling down. Moving but chilling.
How to tell: You’re breathing regularly and can sustain a conversation easily.
Your effort: Above your resting heart rate but below 60% of your max. Anything up to a 5/10 RPE.
Energy source: Your body will use a higher percentage of fat as fuel (as opposed to muscle glycogen—a carbohydrate source). That means you’re tapping into fat from food and fuel sources, not body fat.
Heart Rate Zone 2: Aerobic Activity
What you’re doing: Power walking, jogging or easy running, hiking, a long bike ride. You have a bit more pep in your step. Typically, you’ll do these activities for longer to build up your endurance—they’re sustainable and easy enough for you to do daily. When you think about the guidelines for cardio (the 150-minute-per-week benchmark suggested by the American Heart Association), that’s Zone 2 activity.
How to tell: You should be able to do nasal breathing—inhaling and exhaling through the nose—comfortably during the entire workout. You’re still passing the “talk test” while you move.
Your effort: About 60% of your max heart rate or a 6/10 RPE. Moderate intensity. Melody says these activities shouldn’t put too much demand on you from an energy or muscular perspective. Zone 2 cardio helps you boost your VO2 max, a strong indicator of cardiovascular health trackable on the Insights tab of your obé app under Health metrics (look for ‘Cardio fitness’).
Energy source: Your body is primarily tapping into fat for fuel (again, that’s fat from food sources). This is not a fat-burning zone but a fat-utilization zone.
Heart Rate Zone 3+4: Anaerobic Activity
A note: There’s a lot of overlap between Zones 3 and 4 because it’s hard to sustain any one zone for long. As you level up your training intensity, you’ll oscillate between these heart rate zones. This is the transition zone where you move from aerobic to anaerobic training. While Zone 3 fluctuates between aerobic and anaerobic, Zone 4 primarily works your anaerobic system.
What you’re doing: Running a mile as fast as you can, taking an intense Dance Cardio class (like the Spencer J. variety), doing a HIIT workout. You’re working hard and getting more intentional in your movement, but not hitting your max capacity just yet.
How to tell: You may still be able to inhale through the nose but are getting breathless and have to exhale through the mouth. It’s a noticeable change from Zones 1 and 2. “Your body is getting in oxygen, but because it’s going through fuel so quickly and producing excess carbon, you start exhaling through the mouth to get as much of it out as you can,” says Melody. Fun fact: all the excess carbon also produces lactic acid buildup and DOMS (delayed onset muscle soreness).
Your effort: About 70-80% of your max heart rate for Zone 3 (a 7-8/10 RPE) and 80-90% (an 8-9/10 RPE) for Zone 4. Moderate to vigorous intensity.
Energy source: This type of cardio puts greater demand on your body, so you’ll need to tap into immediate energy reserves. Carbohydrates (muscle glycogen) are your main fuel source. “Your body is saying I need energy, and I need it now,” explains Melody.
Heart Rate Zone 5 Cardio: Anaerobic Activity
What you’re doing: Pushing yourself to your absolute maximum. A super intense HIIT class, a sprint up a hill, anything where you’re going all in, full out. You’re asking a lot of your body.
How to tell: Breathlessness is the name of the game—you’ll have to do open-mouth inhales and exhales to sustain the work. As with Zones 3 and 4, you’re trying to get the excess carbon expelled from the body as quickly as possible—and you need more oxygen to succeed.
Your effort: 90-100% of your max heart rate or a 9-10 RPE. The definition of vigorous intensity.
Energy source: You’re using carbohydrates and often ATP—Adenosine triphosphate—the most readily available carbohydrate source for a cell. A limited supply means this activity level is hard to sustain for long. That’s why most HIIT classes only program 20-30 second work bursts because that’s all you should have capacity for with your ATP reserves when working at max.
What’s the Best Cardio Balance for My Routine?
There’s no magic equation. The most important guideline for determining your ideal training balance? Think about what activity you’ll want to do and stick with.
“There is a wide range of cardio options and a breath of heart rate training zones, but when it comes down to it, they’ll all improve your heart and cardiovascular system,” says Melody. “The benefits of any one zone aren’t substantial enough to push through if something doesn’t feel good to you.”
Still, understanding the differences can help you become more flexible and adaptable in general. For example, if you’re short on time but want to tick off your cardio box, you know a 10-minute HIIT workout will deliver benefits. On the flip side, if you’re not up for something intense, you know a 20-30 minute jog or power walk definitely “counts” as adequate cardio.
“More” or “harder” doesn’t always mean better. If you’re looking to change your body composition, you won’t hit your goal that much faster by pursuing Zone 5 cardio every day. You might over-stress your body, plateau, or hit a wall instead. Love doing HIIT? balance it out with a day or two of Zone 2 steady-state cardio to recover.
“There are benefits to all these types of training,” explains Melody. “The biggest one is developing metabolic flexibility. When you look at the body as a machine and think of all it is capable of, teaching it how to use both fat and carbohydrates as fuel will make you more adaptable. Especially if there are shifts in your life, training, or diet. It makes you more of a chameleon!”
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One response to “The 5 Heart Rate Zones, Explained—Plus Aerobic vs. Anaerobic Fitness”
This was such an interesting blog post! I just got a fitbit, so Imm learning to understand resting and working heart rates. This was helpful!