Training · Aerobic base
Zone 2 Cardio
Zone 2 cardio is steady aerobic exercise at 60 to 70 percent of your maximum heart rate. It is the intensity where fat is the dominant fuel, you can hold a full conversation, and mitochondrial adaptations accumulate with minimal recovery cost. Most coaches call it your aerobic base, easy run pace, or simply long slow distance.
What is Zone 2 cardio?
Zone 2 cardio is any aerobic activity (running, cycling, rowing, swimming, hiking) held at 60 to 70 percent of maximum heart rate for at least 30 continuous minutes. At this intensity you stay below the first ventilatory threshold, fat is the dominant fuel, blood lactate stays near baseline, and the sport does not matter: only the intensity defines the zone.
At this effort level you operate below the first ventilatory threshold, where fat oxidation dominates and blood lactate stays at baseline. The key adaptation is mitochondrial biogenesis: sustained Zone 2 training increases the density and efficiency of mitochondria in slow-twitch muscle fibers, which is the metabolic foundation of endurance performance at every distance.
Elite endurance athletes typically spend 75 to 85 percent of total training volume in Zone 2 or below. This is the "polarized" training model: most volume easy, a small fraction very hard, very little in the middle.
Zone 2 heart rate by age
Zone 2 heart rate is 60 to 70 percent of your maximum heart rate, and because maximum heart rate declines with age your Zone 2 range drops too. At age 30 it is roughly 114 to 133 bpm, at 40 about 108 to 126 bpm, at 50 around 102 to 119 bpm, and at 60 near 96 to 112 bpm.
Max HR estimated as 220 minus age. Use the HR zone calculator for a Karvonen (resting-HR adjusted) result or if you know your measured max HR.
| Age | Est. Max HR | Zone 2 Low | Zone 2 High |
|---|---|---|---|
| 20 | 200 bpm | 120 bpm | 140 bpm |
| 25 | 195 bpm | 117 bpm | 137 bpm |
| 30 | 190 bpm | 114 bpm | 133 bpm |
| 35 | 185 bpm | 111 bpm | 130 bpm |
| 40 | 180 bpm | 108 bpm | 126 bpm |
| 45 | 175 bpm | 105 bpm | 123 bpm |
| 50 | 170 bpm | 102 bpm | 119 bpm |
| 55 | 165 bpm | 99 bpm | 116 bpm |
| 60 | 160 bpm | 96 bpm | 112 bpm |
| 65 | 155 bpm | 93 bpm | 109 bpm |
| 70 | 150 bpm | 90 bpm | 105 bpm |
See the full chart with 5-year increments at Zone 2 heart rate by age.
How to do Zone 2 cardio
Pick an aerobic activity you can sustain for 30 to 90 minutes, strap on a chest heart-rate monitor, and keep your heart rate between 60 and 70 percent of your maximum. If you have no monitor, use the talk test: hold a pace where you can speak a full sentence without pausing to breathe, and expect to go slower than feels natural.
- Heart-rate monitor: Chest strap beats wrist optical for Zone 2 accuracy. Wrist HR lags 20 to 60 seconds and can read 5 to 10 bpm low at easy paces.
- The talk test: No HR monitor? Speak a full sentence out loud. If you can finish it without pausing to breathe, you are in Zone 2. If you gasp, slow down.
- Go slower than you think: Most runners find their Zone 2 pace 60 to 90 seconds per mile slower than their normal easy run. This is normal and expected.
- Minimum 30 minutes: Shorter sessions do not drive the mitochondrial adaptations. If pressed for time, 30 continuous minutes beats two 15-minute sessions.
Gear up
Heart rate monitors athletes actually use
A chest strap keeps you honestly in Zone 2. Wrist optical lags and reads low at easy effort.
- Chest-strap HRMChest straps are far more accurate than wrist optical for Zone 2.View on Amazon →
- Polar H10 chest strapThe accuracy benchmark most labs compare against.View on Amazon →
- GPS watch with HRPairs with a chest strap and records your zones.View on Amazon →
- Armband optical HRMMore accurate than wrist, comfier than a chest strap.View on Amazon →
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8-week Zone 2 base block
A beginner Zone 2 base block starts at 3 sessions per week and builds to 4 sessions over 8 weeks, with lighter recovery weeks at week 4 and week 8. Total weekly Zone 2 volume grows from 90 minutes in week 1 to 200 minutes by week 7, and individual sessions extend from 30 minutes to 50 minutes.
| Week | Sessions | Min / session | Total min | Note |
|---|---|---|---|---|
| 1 | 3 | 30 | 90 | |
| 2 | 3 | 35 | 105 | |
| 3 | 3 | 40 | 120 | |
| 4 | 3 | 30 | 90 | Recovery |
| 5 | 4 | 40 | 160 | |
| 6 | 4 | 45 | 180 | |
| 7 | 4 | 50 | 200 | |
| 8 | 4 | 40 | 160 | Recovery |
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Zone 2 benefits
Zone 2 training increases mitochondrial density and biogenesis, upregulates the CD36 and FABPpm fat-transport proteins, improves fat oxidation, lowers resting heart rate, raises your lactate threshold, and builds a deep aerobic base, all at very low injury and recovery cost compared with high-intensity work.
- Mitochondrial biogenesis: The primary driver. More and more efficient mitochondria means more aerobic ATP per unit of oxygen.
- Fat oxidation: Greater fat-transporter density (CD36 and FABPpm) lets your muscles use more fat at any intensity, sparing glycogen for hard efforts.
- Lactate clearance: Zone 2 trains type 1 fibers to oxidize lactate produced by type 2 fibers, raising the effective lactate threshold.
- Low recovery cost: Unlike threshold or VO2 max work, Zone 2 can be repeated 5 to 7 days per week with negligible accumulated fatigue.
Find your exact zones
Get your Zone 2 ceiling in bpm, plus all 5 zones
Enter your age and resting HR for %HRmax or Karvonen zones.
Open the calculatorZone 2 cardio FAQ
What is Zone 2 cardio?
Zone 2 cardio is aerobic exercise performed at 60 to 70 percent of your maximum heart rate. At this intensity you can hold a full conversation, fat is the dominant fuel, and you accumulate mitochondrial adaptations with minimal recovery cost. Most researchers define it as the upper edge of the aerobic base, just below the first ventilatory threshold.
How long should Zone 2 sessions be?
Minimum effective dose is 30 minutes of continuous Zone 2. Elite endurance athletes accumulate 6 to 12 hours per week, mostly in Zone 2. Recreational athletes benefit from 3 to 4 sessions of 40 to 60 minutes per week. Sessions under 20 minutes are too short to drive meaningful mitochondrial adaptation.
What heart rate is Zone 2?
Zone 2 heart rate is 60 to 70 percent of your maximum heart rate. For a 40-year-old with a max HR of 180 bpm, Zone 2 is roughly 108 to 126 bpm. Use the table below for your age, or use the calculator to account for your resting heart rate.
How do you know if you are in Zone 2?
The talk test: you can speak in full sentences but would prefer not to. Breathing is elevated but not labored. You should be able to sustain the effort for 1 to 3 hours. If you are gasping after a sentence, you are above Zone 2. If you can sing, you are below it.
Is Zone 2 the same as easy running?
Yes, for most trained athletes. Easy pace, conversational pace, and Zone 2 cardio refer to the same aerobic-base intensity. The difference is measurement: Zone 2 uses a heart-rate ceiling (60 to 70 percent of max HR) so you have an objective upper boundary rather than a subjective feel.
How many days per week should you do Zone 2?
3 to 4 days per week is the sweet spot for recreational athletes building an aerobic base. More is better if recovery allows. The Maffetone method recommends keeping all easy training under a strict HR ceiling for 3 to 6 months before adding intensity.
Does Zone 2 burn fat?
Yes. At Zone 2 intensity, roughly 50 to 60 percent of energy comes from fat oxidation versus 20 to 30 percent at higher intensities. This is why Zone 2 is called the fat-burning zone. The metabolic adaptations (more mitochondria, greater fat-transporter density) persist and improve fat burning even at race intensities.
What is the difference between Zone 2 and Zone 3?
Zone 2 is 60 to 70 percent of max HR. Zone 3 (tempo or threshold) is 70 to 80 percent. The key difference is metabolic: Zone 2 stays below the first ventilatory threshold, where fat remains the dominant fuel and lactate does not accumulate. Zone 3 crosses into the "moderate" zone where carbohydrate use rises and recovery costs increase significantly.