Heart rate zones are the most widely used way to describe training intensity, and the most widely misunderstood. Most athletes know they should be doing "zone 2," fewer know what number that actually is for them, and fewer still know that the answer changes depending on which method their watch is using.
This guide covers what the zones mean, the three ways to set them, how to find the numbers they depend on, and how to distribute your training week across them. Here is the whole thing in one picture.
The five training zones at a glance
Zones are slices of one continuous intensity scale, from easy to all out. Most of your training belongs at the easy end.
of your weekly training time, in a typical base-phase week
| Zone | % of max HR | How it feels | Share of week |
|---|---|---|---|
| 1. RecoveryFull conversation | 50 to 60% | Full conversation | 15% |
| 2. EnduranceComplete sentences | 60 to 70% | Complete sentences | 65% |
| 3. TempoShort phrases only | 70 to 80% | Short phrases only | 5% |
| 4. ThresholdA few words at a time | 80 to 90% | A few words at a time | 10% |
| 5. VO2 maxNo talking | 90 to 100% | No talking | 5% |
Shares are illustrative for a base-phase week and shift with your event and where you are in a training block. Zone boundaries are conventions, not physiology.
Why zones exist at all
Your body does not have five discrete gears. Intensity is a continuum, and zones are lines drawn on it for convenience. What makes those lines useful is that they roughly track real physiological transitions: the point where you start relying more on carbohydrate than fat, the point where lactate begins to accumulate faster than you clear it, and the point where you are working at or near your maximum oxygen uptake.
Training at different points on that continuum produces different adaptations. Easy aerobic work builds capillary density, mitochondrial volume, and the ability to burn fat, all of which raise your ceiling over months and years. Threshold work raises the intensity you can hold before lactate runs away from you. Short, very hard intervals push your VO2 max. Zones are shorthand for aiming at one of those adaptations on purpose rather than by accident.
The five zones
Zone 1, recovery. Genuinely easy. Warm-ups, cool-downs, and shakeout sessions. You should be able to hold a full conversation without noticing your breathing. Its job is to move blood without adding meaningful training stress.
Zone 2, endurance. Easy aerobic work, and the foundation of endurance training. You can still talk in complete sentences, though you would rather not give a speech. This is where most of your weekly hours belong, and where most amateur athletes spend far too little time because it feels too easy to be productive.
Zone 3, tempo. Moderately hard, sometimes called the grey zone. Talking gets clipped to short phrases. Zone 3 is not useless, and it has a real place in marathon-specific work, but it is where undisciplined training tends to pool: too hard to recover from properly, not hard enough to drive the adaptations that hard sessions are for.
Zone 4, threshold. Work at or near your lactate threshold, roughly the hardest effort you could sustain for about an hour. A few words at a time, not sentences. This is the classic tempo or threshold interval session, and it directly raises the pace you can hold in a race.
Zone 5, VO2 max. Short, hard intervals, typically measured in minutes rather than tens of minutes. Talking is not happening. Highly effective in small doses and highly effective at digging you into a hole if you overdo it.
Three ways to set your zones
This is where most of the confusion comes from. Two athletes with identical fitness can end up with different zone boundaries because they anchored them differently.
Percentage of max heart rate. The simplest method: each zone is a slice of your maximum, with zone 2 usually falling around 60 to 70 percent. It only needs one number. Its weakness is that it ignores your resting heart rate entirely, so it treats a well conditioned athlete and an untrained one identically if they happen to share a max.
Karvonen, or heart rate reserve. This works from the gap between your resting and maximum heart rate, then applies the zone percentages to that reserve and adds your resting rate back on. Because it accounts for how low your resting heart rate sits, it individualizes the boundaries and generally places them higher in bpm than the plain percentage method. If you have ever wondered why your watch's zone 2 feels harder than a friend's, this is often why.
Threshold, or LTHR. Anchors everything to your lactate threshold heart rate instead of your max. This is the method most coaches prefer if the number is available. Threshold is trainable and moves as you get fitter, it is far easier to measure safely than a true max, and it sits at the boundary that actually matters for racing. Note that the percentages look completely different: threshold work sits near 100 percent of LTHR by definition, so a zone 2 of 85 to 90 percent of LTHR is not a typo.
Run the numbers
The heart rate zone calculator gives you all five zones in beats per minute using any of these three methods, so you can see how much the boundaries move depending on which one you pick.
Finding your max heart rate
The familiar 220 minus age is the worst option in common use. It was never intended as a precise formula, and it runs high for young athletes and low for older ones, with a standard deviation of over ten beats either way. Tanaka's formula, 208 minus 0.7 times your age, tracks measured values noticeably better, and it is what our calculator uses when you estimate from age.
Better than any formula: use the highest heart rate you have genuinely seen. If you have raced a hard 5K or done a set of maximal hill repeats with a chest strap, the peak from that effort is a far better working max than anything an equation will hand you. Best of all is a proper test, supervised, or a lab assessment.
For threshold heart rate, the standard field test is a 30 minute all-out time trial, alone, on flat ground. Your average heart rate over the final 20 minutes is a good estimate of LTHR.
How to spend your week
The distribution matters more than the precision of the boundaries. The most consistent finding in endurance training research is that successful athletes across sports skew heavily easy: roughly 80 percent of training time at low intensity, 20 percent at threshold and above. The instinct to spend every session at a moderately hard effort is exactly the pattern that produces plateaus.
That does not mean 80/20 by session count, or that the split is fixed. It shifts with your event, your training age, and where you are in a block: a base phase leans further toward easy work, a race-specific phase adds more threshold and race-pace volume.
Zones are guide rails, not rules
Heart rate lags effort, drifts upward over long sessions, and rises with heat, dehydration, altitude, caffeine, and poor sleep. A number that is ten beats off on a hot day is not a reason to push harder. Effort and how you feel get the final say.
Where this fits with pace
Heart rate and pace answer different questions. Pace tells you what you produced; heart rate tells you what it cost. On a hilly course or a hot day the two diverge sharply, which is why most well-built sessions prescribe one as the target and use the other as a check.
Once you know your zones, pair them with target paces using the running pace calculator, and see what your current fitness is worth on race day with the race time predictor.
The part zones cannot tell you
Knowing your zones tells you how hard to go once you know what today's session is for. It does not tell you whether today should be a threshold session at all, or whether the fatigue you are carrying means the smart call is to move it. That judgment, applied consistently over months, is most of what a coach actually does.
That is the part Vaast automates. It reads your training and recovery data, prescribes each session in the right zone, and adjusts when your body says to back off, so the plan reflects the athlete you are this week rather than the one you were when you wrote it down.