It’s your long run day, and you’ve mapped out your route, packed all your fuel, and double-knotted your laces. But have you figured out where your long run heart rate zone should be? It may not seem like an important part of planning, but to maximize the benefits of all those miles, you actually want to keep your heart rate in a pretty specific place.

To take a step back, let’s clarify what we mean by “long run.” Your long run is, well, the longest run of your week, says Peloton instructor Matt Wilpers. The exact mileage can vary widely based on your fitness levels and goals: It might be six miles if you’re a beginner, or more than 20 miles if you’re training for an ultramarathon. “Some coaches use a rule of thumb that the long run falls within 20 to 30 percent of your total weekly mileage,” Matt says. 

Regardless of exactly how long your long run is, you want to approach it strategically—and that includes keeping your heart rate in mind. Here’s what experts want you to know about your heart rate during a long run, including why it matters, and how to successfully keep yours in check even as the miles add up. 

What Is the Ideal Heart Rate Zone for a Long Run?

For a typical, easy-paced long run, Matt suggests aiming for about 60 to 70 percent of your maximum heart rate, often referred to as “zone 2” cardio. (To get an estimate of your max heart rate, subtract your age from 220. Then multiply that by 60 percent to find the low end of this range, and by 70 percent to find the high end.)

This will feel like a casual, conversational pace that you could hold for hours while easily chatting with a friend. “In general, your long run should usually be done at a slow and steady pace because the difficult part of the run is simply the distance/time,” Matt says. “The goal is to build endurance.”

Why Your Long Run Heart Rate Matters

During a long run, monitoring your heart rate is crucial because it serves as an effective proxy for your oxygen consumption, which helps to indicate your effort level. As John Mercer, PhD, a professor of kinesiology and nutrition sciences at the University of Nevada, Las Vegas, explains, “rate of oxygen consumption tells you how active your aerobic metabolism is.” For a sustained effort like a long run, you want to primarily rely on the aerobic energy system (rather than the anaerobic energy system). Aerobic metabolism efficiently utilizes oxygen to fuel your muscles, enabling you to exercise for an extended period. Anaerobic metabolism, on the other hand, relies on limited stores of glycogen (a form of glucose or sugar) in your muscles to power high-intensity, short-burst activities like sprinting, and can only fuel you for a short period of time. Keeping your effort level in check by monitoring your heart rate during a long run helps ensure you stay in that aerobic zone, preserving muscle glycogen so you can continue running.

This is why many people plan their runs by heart rate training zones: “In Zone 1 and 2, you're below the intensity where the anaerobic system starts to be active,” Mercer says. “Zone 3 and 4 are right around that range where the anaerobic system is really starting to kick in. And then zone 5 is well above that intensity.”  

There are several reasons why it’s beneficial to keep your heart rate in check and stay in that aerobic zone during a long run.

For starters, keeping your heart rate around zone 2 helps increase your endurance to tackle longer distances without totally wearing yourself out. “You’re building endurance without accumulating excessive fatigue,” Matt explains. That means you won’t be so tired that you can’t pull off workouts scheduled later in the week. He points out that fatigue is not only physical, but also mental—if your long runs are too hard, you both run the risk of injuring yourself and are more likely to burn out. “Letting the heart rate get too high on these runs can put you at great risk of overtraining,” he says.

Matt adds that keeping your heart rate down also means you’re training your body to use fat for fuel. “When your heart rate creeps up, you risk missing out on adapting your body to fat metabolizing for energy,” he says. “This means you will dig deeper into your glycogen stores for energy than you otherwise would.” Since your body can only store a limited amount of glycogen, you’ll eventually hit the wall and feel overwhelming fatigue once those stores run out—unless your body is adapted to using fat as fuel (or you’re consistently refueling with lots of carbs so you never get to that point).  

There’s also something to be said for training your mindset. “Mentally, [keeping your heart rate down] teaches you to relax and settle into a pace,” Matt says. This can come in handy during those early miles of a race when you want to get into a smart rhythm without pushing too hard too soon. 

On the other hand, you want to ensure that you’re getting your heart rate to at least 60 percent of your maximum. If you’re jogging so slowly that it doesn’t quite hit that target, you’re not getting an adequate training stimulus and will miss out on the endurance-building benefits of a long run, Matt says.  

Tips for Sticking to Zone 2 During a Long Run

As anyone who’s ever tried to stay in zone 2 during a run can attest, it can be surprisingly tricky to keep your heart rate below that 70 percent threshold. 

It’s very common for runners to take their long runs too fast. “Sometimes the pace is getting faster and you don't realize it,” Matt says. “Don’t be afraid to slow down.” He suggests wearing a fitness tracker or smartwatch to keep an eye on both your heart rate and pace so you can ease off the gas when necessary. 

If you’ve decreased your pace and your heart rate is still too high, Matt suggests focusing on your breath. “Try nose and mouth breathing using techniques like 2-2 breathing (two footsteps breathe in, two footsteps breathe out),” he says. You can also try shortening your stride and increasing your cadence to spend less energy while going the same speed, he adds. Or, add in some walk intervals to bring your heart rate under control. 

However, be aware that your heart rate may increase as you get further into a long run. “A certain level of cardiac drift is normal,” Matt says. “This is where your heart rate drifts higher during a long run despite going at the same pace. It happens as fatigue, dehydration, and/or heat sets in and your body has to work harder over time to maintain the same pace.”

At the end of the day, remember that heart rate is an imperfect measurement. “Heart rate is a predictor of oxygen consumption, but it’s not a one-for-one,” Mercer says. “There are times that heart rate goes up and it has nothing to do with the rate of oxygen consumption.” If you’re basing your heart rate training off a smartwatch or fitness wearable, also keep in mind that most don’t track heart rate with 100-percent accuracy, either. Finally, Mercer adds an important caveat that if you’re on medication like beta-blockers that slow your heart rate, there’s no point in using this measurement to gauge your exercise intensity.

If you’re mid-run and you find yourself getting overly stressed about your heart rate, try to just let go, Matt suggests. “Instead, focus on effort,” he says. A better goal might be to simply aim for an effort level or rate of perceived exertion (RPE) of 2-3 on a scale of 0 to 10, he says. “Try to maintain an effort where you can easily talk: If you can comfortably hold a conversation with complete sentences, you’re probably close to where you need to be,” he says.

When It’s OK to Push Into a Higher Long Run Heart Rate Zone 

There are some long runs where runners will throw all of this out the window. “Not all long runs are meant to be at the same intensity,” Matt says. “Some include speed work.” 

If you’re a more advanced runner who’s already built up your endurance base, it can be beneficial to occasionally add some harder intervals into your long run—in which case your heart rate will certainly fluctuate, spiking up higher than 70 percent of your max. 

Matt says this strategy can be great to practice running at your goal or race pace (or even a little faster) when your legs are tired. “It’s about getting your body used to running fast while running long,” he says. This can improve your fatigue resistance and your body’s ability to clear blood lactate (which accumulates in your muscles along with excess hydrogen ions and creates a more acidic environment, bringing on that muscle burn). Moving at a faster clip can also clean up your running mechanics: “Your body is forced to find its own path of least resistance to running faster over long distances,” Matt says. 

Plus, there’s the mental benefit: Adding harder efforts to your long runs is “great for improving mental toughness and being able to be comfortable with discomfort,” Matt says. He adds that after doing this kind of workout, your normal long run will feel easier. 

Just know that adding harder efforts into a long run takes a lot out of the body, so program these workouts sparingly and with plenty of time for recovery. Many pros will only do them once every other week, and only when they’re deep into race prep. “Do them later in the training cycle to avoid burnout or peaking too early,” Matt says. He suggests waiting until you’re about eight to 10 weeks out from race day to try this. 

The Takeaway

In general, doing your long runs in heart rate zone 2—i.e., between 60 and 70 percent of your maximum heart rate—will help ensure you’re getting the endurance-building benefits out of your miles without pushing yourself so hard you end up overtraining. Although there’s a place for adding a bit of speed work into your long run, most of the time, you want to keep these miles slow and steady. You’ll be glad you did when you’re able to show up to the start line of your race healthy and ready to tackle the full distance all the way to the finish line.