Heart rate zones aren’t theoretical. They’re the difference between a run that builds your aerobic engine and a run that just leaves you tired. Every run you do has a purpose — and your zone tells you whether you’re hitting it.
This post walks through all six McMillan heart rate zones from a runner’s-eye view. What does Zone 2 actually feel like when you’re 40 minutes in? What’s the difference between a Zone 4 tempo run and a Zone 5 cruise interval? When are you supposed to be in Zone 6 — and how often?
If you don’t have your zones set up yet, start here:
→ Calculate your 6 heart rate zones with the McMillan Heart Rate Zone Calculator
Otherwise, let’s go zone by zone.
Why Runners Should Train by Heart Rate (In Addition to Pace)
Pace tells you how fast you’re moving. Heart rate tells you how hard your body is working to move you. They’re related — but on any given day, the same pace can feel completely different.
Hot weather, poor sleep, low fuel, the cumulative fatigue of a hard training week — all of these push your heart rate up at any given pace. If you only train by pace, you’ll hammer through workouts that should have been easy, just because the watch said the pace was easy. If you only train by heart rate, you’ll back off on cool days when your body could have handled more.
The right answer is both. Pace is the dial you set; heart rate is the feedback that tells you whether the dial was set correctly today. That’s why Greg’s coaching system pairs pace targets (from the McMillan Running Calculator) with heart rate ranges (from the Heart Rate Zone Calculator) — neither one is the whole picture by itself.
The 6 McMillan Running Heart Rate Zones
The McMillan system uses six zones rather than the typical five. The reason is simple: lactate threshold training is where most race fitness lives, and lumping it into a single zone loses critical resolution. The McMillan system splits the threshold range into three zones — slightly below threshold (Zone 3), at threshold (Zone 4), and slightly above threshold (Zone 5) — so you can target each adaptation precisely.
All zones below are expressed as percentages of heart rate reserve (HRR), calculated using your max HR and resting HR via the Karvonen formula. If you haven’t got your numbers yet, the how-to-calculate guide walks you through the setup, and the Max Heart Rate Calculator covers how to find your real max HR with the McMillan Field Test.
Zone 1 — Recovery Jogs (55–65% HRR)
What it feels like: Slow jog or even walking-pace easy. You can talk in full sentences without any breath effort. This is slower than your normal easy run.
What it’s for: Active recovery between hard sessions. Recovery jogs after a track workout. The very gentle running you do between repeats in an interval session. Zone 1 is about getting blood flowing to flush out the previous workout, not about training adaptation.
Common mistake: Treating Zone 1 as a “real” run. If your recovery jog is anywhere near your normal easy pace, it’s not a recovery jog — it’s just a slow easy run, and you’re stealing recovery from your hard sessions.
Zone 2 — Easy and Long Runs (55–78% HRR)
What it feels like: Conversational. You can hold a full conversation without gasping. Breathing is steady and quiet. This is the pace where you can let the miles roll by.
What it’s for: The bulk of your weekly mileage. Easy runs, long runs, the slow-to-moderate base-building work that grows your aerobic engine. Zone 2 is where mitochondrial density goes up, capillary networks expand, and your body learns to burn fat efficiently. It’s an important zone for every distance runner.
Common mistake: Running Zone 2 too fast. Many distance runners do this. If your breathing has shifted from “barely noticeable” to “noticeably faster,” you’ve drifted out of Zone 2 and into Zone 3 — and you’re not building the aerobic base you think you are.
For a deep dive on Zone 2 specifically, see our full Zone 2 Heart Rate Calculator and training guide.
Zone 3 — Early Threshold / Steady State (75–80% HRR)
What it feels like: Easy-medium effort. Your breathing is heavier than easy but not labored. You can still talk, but in shorter sentences — a few words between breaths rather than continuous conversation.
What it’s for: Steady-state runs and steady state interval. Long progression efforts where you build into a moderate effort and hold it–as well as shorter repetitions as in the Norwegian Method. Zone 3 sits just below lactate threshold — the goal is to spend extended time at an intensity your body can clear lactate from indefinitely.
Common mistake: Drifting up into Zone 4 mid-workout. Steady-state runs are supposed to feel boring-comfortable; if your breathing kicks up and you’re suddenly working hard, your HR has crept across the threshold line and you’ve turned a steady state workout into a tempo session. Back off.
Zone 4 — Lactate Threshold (80–85% HRR)
What it feels like: Comfortably hard. This is the classic “tempo” effort — sustainably hard. You can squeeze out a couple of words at a time but holding a conversation is out of the question.
What it’s for: Tempo runs (15–40 minutes continuous at threshold) and tempo intervals (longer reps, around 8–15 minutes, with short recovery). Zone 4 is where you train your body to clear lactate faster — the single biggest determinant of race performance for most distance events.
Common mistake: Going too fast on tempo runs. Greg says it often: with Stamina workouts, challenge yourself to go longer at a given pace, not faster. A 30-minute tempo at solid Zone 4 will produce more adaptation than a 15-minute tempo that drifted into Zone 5.
Zone 5 — High Threshold / Cruise Intervals (82–87% HRR)
What it feels like: Hard but controlled. Faster than threshold, slower than VO2max. You’re working — breathing is loud, conversation is impossible — but you’re not on the edge.
What it’s for: Cruise intervals (Jack Daniels’ term — Greg uses it too). Repeats of 3–8 minutes at slightly faster than tempo pace, with short recovery. The point is to spend more total time just faster than your lactate threshold than you could in one continuous tempo run, because the recoveries let you push the work repeats slightly harder.
Common mistake: Treating Zone 5 like Zone 6. Cruise intervals aren’t VO2max work — they should still feel sustainable for the duration of the interval, just barely. If you’re hanging on for dear life by the second rep, you’ve started a different workout.
Zone 6 — Speed and Sprint Workouts (90–100% HRR)
What it feels like: Hard. Your heart rate may not even fully catch up to the effort during shorter reps — VO2max intervals work the engine faster than HR can climb. By the end of a longer interval, you’re approaching your max.
What it’s for: VO2max intervals (400m to 2000m repeats), strides, sprints, anaerobic capacity work. Zone 6 trains the top end of your engine — your maximum oxygen uptake and your ability to tolerate hard efforts.
Common mistake: Doing too much of it. Zone 6 work has a tiny dose-response window — a small amount produces big adaptation, but more isn’t always better.
Sample Stamina-Phase Training Week (Level 4)
Here’s how the zones might map across a Stamina-phase week from a McMillan Level 4 plan — an intermediate-to-advanced volume runner mid-cycle, with the focus on building threshold fitness:
| Day | Workout | Primary Zone |
|---|---|---|
| Monday | 30-min recovery jog | Z1 |
| Tuesday | Tempo intervals: 3 × 10 min @ Z4 with 2-min easy jog recovery | Z4 (work) / Z2 (recovery) |
| Wednesday | 45-min easy run | Z2 |
| Thursday | Steady-state run, 35 min @ Z3 | Z3 |
| Friday | Rest or 30-min recovery jog | Z1 |
| Saturday | Long run, 1h 30min, with last 20 min progression to Z3 | Z2 → Z3 |
| Sunday | 50-min easy run + 6 × 100m strides | Z2 + brief Z6 |
Total: ~5.5 hours of running, mixing Stamina-zone work (Z3–Z4 on Tuesday and Thursday) with the easy aerobic work that supports it. The long run is the cornerstone — every other workout in the week is built around protecting Saturday’s effort and recovering from it.
Workouts shift across the training cycle. Base phases lean heavier on Z2 and lighter on Z5–Z6. Race-specific phases dial up the threshold and VO2max work. The mix isn’t a fixed ratio — it changes with the phase, the runner, and the goal race.
→ Calculate your zones now with the McMillan Calculator Free. No signup.
Frequently Asked Questions
Zone 2 is the aerobic-base training zone — typically defined a 55–78% of your heart rate reserve (HRR) in the McMillan system. It’s the easy-run, conversational-pace zone where your body builds aerobic capacity by improving fat oxidation, mitochondrial density, and capillary networks. Most distance runners should spend the majority of their weekly mileage in Zone 2.
The most accurate method uses heart rate reserve (HRR): Zone 2 = (HRR × 55%) + Resting HR for the bottom of the range, and (HRR × 78%) + Resting HR for the top, where HRR = Max HR − Resting HR. Or just plug your numbers into the Zone 2 calculator at the top of this page — it’ll do the math for you.
Three reasons typically. First, you’ve been training above Zone 2 (most runners do their easy runs too hard). Second, your aerobic system needs time to adapt — Zone 2 pace gets faster within 8–12 weeks of consistent training. Third, environmental factors like heat and humidity push HR up at any given pace, making the pace feel artificially slow on hot days. Be patient. The pace will come.
For runners building an aerobic base or returning from a layoff, the answer is “as much as your weekly mileage will support.” Even for runners deep in race-specific training, Zone 2 should remain the dominant intensity, with the harder sessions layered in on specific days as the training cycle progresses.
You can — and many beginners and base-building runners do. But a complete training plan also includes hard sessions in Zones 4 (threshold) and 6 (VO2max) to build the top-end fitness needed for racing. A 100% Zone 2 plan builds aerobic capacity but leaves you without the lactate-clearance and VO2max adaptations that determine race performance.
Zone 2 is the zone where your body burns fat as its primary fuel, so yes — it’s effective for fat oxidation. That said, total energy expenditure across the whole week matters more than the specific zone you train in. Consistent running of any kind tends to improve body composition over months; the zone matters less than the consistency.
Yes. The physiology of Zone 2 — fat oxidation, mitochondrial development, capillary growth — is the same regardless of gender. The HR ranges differ slightly because max HR formulas often need to account for sex (the Gulati formula is the most accurate age-based formula for women), but once you have your accurate max HR, the Zone 2 calculation works the same way.
Related Reading
- McMillan Heart Rate Zone Calculator — The tool. HRR-based, 6 personalized zones, free
- How to Calculate Your Heart Rate Zones — Methodology deep dive: age-based, Karvonen, and lactate threshold methods
- Max Heart Rate Calculator — How to find your real max HR with the McMillan Field Test
- Zone 2 Heart Rate Calculator — Everything you need to know about training in the aerobic sweet spot
Written By Greg McMillan
Called “one of the best and smartest distance running coaches in America” by Runner’s World’s Amby Burfoot, Greg McMillan is renowned for his ability to combine the science of endurance performance with the art of real-world coaching. While getting his graduate degree in Exercise Science he created the ever-popular McMillan Running Calculator – called “The Best Running Calculator” by Outside Magazine. A National Champion runner himself, Greg coaches runners from beginners to Boston Qualifiers (15,000+ and counting!) to Olympians.
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