You head out for your usual easy run. Your watch shows the same pace as last week, but it's 15 degrees warmer, and by mile 2 your heart rate is 15 beats higher than it was. Pace says nothing changed. Your heart says this run cost a lot more. Heart rate zones for running measure that cost directly, which makes them a better guide than pace for most training runs.
Why Heart Rate Beats Pace for Zone Training
Pace is a useful tool for race planning. For training, it has a major flaw: the same pace puts different stress on your body depending on conditions. A 9-minute mile in 85°F heat with 75% humidity is harder on your cardiovascular system than the same pace on a cool morning. An uphill segment spikes your heart rate while your pace slows. Fatigue from yesterday's workout changes how hard today's run feels at the same pace.
Heart rate reflects what your cardiovascular system is doing right now. When you target a zone by heart rate, you're targeting the training effect itself. That makes heart rate the more consistent guide for easy and steady runs, where the goal is a specific effort. Pace still matters on race day and for some interval sessions.
The 5 Running Zones
All 5 zones come from your heart rate reserve, the gap between your resting and max heart rate, using the Karvonen formula. Because your resting heart rate is part of the math, your zones reflect your fitness as well as your age. Measure your resting heart rate in the morning before you get out of bed, then use the calculator to get your personal zone numbers. The table below shows the intensity of each zone. Swimming works differently. Your max heart rate runs lower in the water, so see heart rate zones for swimming before you take these zones to the pool.
| Zone | % HRR | Effort Feel | Primary Fuel | Best For |
|---|---|---|---|---|
| Zone 1 | 50–60% | Easy, walking pace | Fat | Active recovery, warmup/cooldown |
| Zone 2 | 60–70% | Comfortable, can hold conversation | Mostly fat | Aerobic base, fat burning, long runs |
| Zone 3 | 70–80% | Moderately hard, sentences get shorter | Mixed | Aerobic endurance (use sparingly) |
| Zone 4 | 80–90% | Hard, can speak a few words | Mostly carbs | Lactate threshold, tempo runs |
| Zone 5 | 90–100% | Maximum, cannot speak | Carbs | VO₂ max, speed intervals |
Here's the math for a 35-year-old runner with a resting heart rate of 55 bpm. Each zone equals resting heart rate plus a percentage of heart rate reserve.
Max HR = 220 − 35 = 185 bpm
HRR = 185 − 55 = 130 bpm
Zone 1 = 55 + (0.50–0.60 × 130) = 120–133 bpm
Zone 2 = 55 + (0.60–0.70 × 130) = 133–146 bpm
Zone 3 = 55 + (0.70–0.80 × 130) = 146–159 bpm
Zone 4 = 55 + (0.80–0.90 × 130) = 159–172 bpm
Zone 5 = 55 + (0.90–1.00 × 130) = 172–185 bpm
A second runner the same age with a resting heart rate of 65 bpm has a heart rate reserve of 120 bpm, which puts Zone 2 at 137 to 149 bpm. Same age, same max heart rate, and a different easy-run target. A chart based on age alone would give both runners the same zones.
Zone 1: Recovery Running
Zone 1 is 50 to 60% of heart rate reserve, a comfortable effort that most people associate with a brisk walk or a slow jog. On its own it does little to build fitness, but it has 2 jobs in a training week.
First, it's a good fit for active recovery days between hard sessions. Light movement keeps blood flowing without adding training stress. Second, warmup and cooldown segments in Zone 1 prepare your cardiovascular system for harder efforts and bring it back down afterward.
Zone 2: Your Aerobic Base
Zone 2 (60 to 70% HRR) is where most of your running mileage should happen, especially if you're building a base or training for endurance. At this intensity, your body runs mostly on fat, builds more mitochondria in slow-twitch muscle fibers, and develops the aerobic capacity every other zone depends on.
The test for Zone 2 is whether you can hold a full conversation in complete sentences. Your breathing is elevated but controlled, and you feel like you could keep going for hours. For most recreational runners, this means running well below their default "comfortable" pace.
For more on this zone, see the fat burning heart rate zone guide and the complete Zone 2 training guide.
Zone 3: The Gray Zone
Zone 3 (70 to 80% HRR) is moderately hard. You can still speak, in shorter bursts. It's the zone most recreational runners drift into on their "easy" days when they push a little harder than they should.
The problem with Zone 3 is that it sits in an awkward middle ground. It's hard enough to pile up fatigue and leave you needing extra recovery before your next hard day, and too easy to deliver the adaptations of Zone 4 and 5 work. Too much volume here, often called "junk miles," leads to more fatigue with little extra fitness to show for it.
Zone 3 has its place in training, including some long runs and marathon pace work. In the polarized training model, though, it's kept to a minimum in favor of more Zone 2 volume and sharper Zone 4 and 5 work. In a 2014 study of 48 well-trained endurance athletes, 9 weeks of polarized training raised VO₂ peak by 11.7%, a bigger gain than threshold-heavy, high-intensity, or high-volume plans produced.
Zone 4: The Tempo Zone
Zone 4 (80 to 90% HRR) is where tempo runs live. It's comfortably hard: your breathing is labored, and you can talk only in short phrases. This zone sits around your lactate threshold, the point where lactate starts building up in your blood faster than your body can clear it.
Training in Zone 4 raises that threshold over time, so you can run faster before fatigue sets in. That pays off in any race from a 5K to a marathon. Classic Zone 4 workouts include 20 to 40 minute tempo runs and cruise intervals, such as 3 to 5 repeats of 8 to 12 minutes at threshold with short rest between them.
These sessions take real recovery. Most runners should do no more than 1 or 2 Zone 4 sessions per week, with Zone 1 or 2 runs between them.
Heart rate reserve isn't the only way to define that threshold zone. Joe Friel's LTHR-based zone system builds all 7 of its zones from a tested lactate threshold heart rate instead.
Zone 5: Speed and VO₂ Max
Zone 5 (90 to 100% HRR) is maximum intensity. You can't speak, and you're working as hard as you can hold for a few minutes. This is the zone that trains your VO₂ max, the ceiling of your aerobic power.
Zone 5 work is usually done in short intervals: 400m to 1,600m repeats at near-maximum effort with full recovery between them. It builds speed, improves running economy at race pace, and raises your aerobic ceiling. It also takes a lot out of you. Most runners do best with 1 Zone 5 session per week at most, with plenty of Zone 2 volume around it.
How to Structure a Running Week by Zone
Here's a sample week for a newer runner working toward half-marathon fitness, with 4 runs plus an optional recovery jog:
| Day | Run Type | Zone | Duration |
|---|---|---|---|
| Monday | Easy run | Zone 2 | 40–50 min |
| Tuesday | Rest or cross-train | Zone 1 | – |
| Wednesday | Tempo run | Zone 4 | 35–45 min (20 min threshold effort) |
| Thursday | Easy run | Zone 2 | 35–45 min |
| Friday | Rest | – | – |
| Saturday | Long run | Zone 2 | 70–90 min |
| Sunday | Rest or recovery jog | Zone 1 | 20–30 min |
Only about 10% of this week's running time is hard, which is lighter than a true 80/20 split. That's on purpose for a newer runner. Once a few weeks like this feel comfortable, add a short Zone 5 session on Friday, such as 5 repeats of 3 minutes hard with 3 minutes easy between them, and keep Saturday's long run easy.
Tracking this structure over several weeks is where it pays off. A running log that imports from your GPS watch, like the free one at Run Hive, makes it easy to see whether your Zone 2 days stay in Zone 2 and whether your Zone 4 sessions trend the right way over a training block.
Common Heart Rate Zone Mistakes in Running
Most runners undo their own zone training with 1 of these 3 habits.
Running Zone 2 too fast. This is the most common error. Most runners have heard "easy runs should feel easy" and still set their pace by habit. If you're in Zone 3 or even Zone 4 on your "easy" days, you're piling up more fatigue than the workout calls for.
Ignoring heat and humidity. In warm conditions, your heart has to pump more blood at the same pace, so your heart rate runs higher than usual at a given speed. Slow down to keep your heart rate in zone, and let the pace fall where it falls.
Using wrist optical HR for intensity work. Wrist-based optical sensors can lag behind your true heart rate when effort changes quickly, which makes them less reliable for short Zone 4 and 5 intervals. In a 2017 study of 50 adults, a chest strap matched an ECG more closely than any wrist or forearm monitor tested. A chest strap (Garmin, Polar, Wahoo) reads the heart's electrical signal and responds faster, which matters most for threshold and speed work.
Frequently Asked Questions
What heart rate zone is best for running to lose weight?
Zone 2 (60 to 70% of heart rate reserve) is the best default for most runners. Weight loss comes down to total calories burned over the week, and Zone 2 runs are easy enough to repeat 3 or 4 times a week for 45 to 90 minutes without wearing you down. Harder runs burn more calories per minute and need more recovery, so a Zone 2 base plus 1 harder session a week works well for most people. See heart rate zones for weight loss for the full breakdown.
What is the best heart rate zone for marathon training?
Marathon training is mostly built on Zone 2. Research on elite endurance athletes finds they spend roughly 80% of their training at easy, conversational intensity (Zones 1 and 2) and about 20% at hard intensity (Zones 4 and 5, tempo and interval work). Zone 2 builds the aerobic base and fatigue resistance you need to run 26.2 miles. Harder work builds speed and raises your lactate threshold, and it pays off most when it sits on a solid Zone 2 base.
How much of running training should be in Zone 2?
Research on elite endurance athletes points to 75 to 85% of training volume in Zones 1 and 2, with the remaining 15 to 25% in Zones 4 and 5. This 80/20 split is often called polarized training. Zone 3, the "moderately hard" gray zone, tends to be the least productive zone for most runners because it's taxing to recover from and too easy to drive the adaptations of true threshold work.
Why does my heart rate spike during easy runs?
Heat and humidity, hills, a short warmup, and dehydration all push your heart rate up during easy runs. Heart rate runs higher in warm weather at the same pace, climbs fast on uphills, and takes 5 to 10 minutes to settle after you start. New runners also see more spikes while their aerobic fitness develops. If your heart rate keeps climbing past Zone 2 on an easy effort, slow down, even to a walk-jog, until it settles.
What does running in Zone 4 do?
Zone 4 (80 to 90% of heart rate reserve, or HRR) sits around your lactate threshold, the point where lactate starts building up in your blood faster than your body can clear it. Training in Zone 4 raises that threshold, so you can run faster before fatigue sets in. It's the main zone for tempo runs. Zone 4 work is effective and takes real recovery, so most runners should do no more than 1 or 2 Zone 4 sessions per week, with easy Zone 1 or 2 days in between.
This article is for informational purposes only and does not constitute medical advice. Please consult a physician or certified fitness professional before starting a new exercise program.