Concepts
Zones
How Runtool builds training zones — the thresholds every boundary is anchored to, where those anchors come from, what the starting estimates are worth, and how zone definitions are versioned.
Zones turn "run comfortably hard" into a number you can hit. Runtool prescribes running with pace zones and tracks effort with heart rate zones; every workout target and every time-in-zone chart reads from them. Zones live under Settings → Zones for each athlete — see Athlete settings.
Every boundary is a threshold
Runtool's zones are not slices of your maximum. They are built around three points in your physiology:
| Anchor | What it is |
|---|---|
| LT1 | Aerobic threshold — the fastest you can run while lactate stays near resting levels |
| LT2 | Lactate turnpoint — the hardest effort you can hold steadily, roughly an hour at best |
| vVO₂max | The speed at which you reach maximum oxygen uptake — around 3K race pace |
Every zone boundary is one of those three, or a fixed step from one:
| Boundary | Sits at | Meaning |
|---|---|---|
| Z1 / Z2 | 10% slower than LT1 | recovery ends, easy running begins |
| Z2 / Z3 | LT1 | the top of genuinely easy running |
| Z3 / Z4 | midway between LT1 and LT2 | tempo ends, threshold work begins |
| Z4 / Z5 | LT2 | the turnpoint — above it you're on the clock |
| Z5 / Z6 | vVO₂max (≈13% faster than LT2) | intervals end, repetitions begin |
The six zones that fall out of it:
| Zone | Name | What it is |
|---|---|---|
| Z1 | Recovery | Easier than easy — active recovery |
| Z2 | Endurance | Everyday aerobic running, up to LT1 |
| Z3 | Tempo | Between LT1 and marathon effort — comfortably hard |
| Z4 | Threshold | The LT2 band — sustained hard running |
| Z5 | VO₂max | Interval pace — maximal aerobic power |
| Z6 | Anaerobic | Faster than VO₂max — repetition and sprint work |
Most training lives in Z2. The zones exist so that easy days stay genuinely easy and hard days hit the intensity they're designed for.
Why thresholds and not percentages of your maximum
Most training plans you'll have met split intensity by percentage: 60/70/80/90% of maximum heart rate, or the same split applied to heart-rate reserve (the Karvonen method, from a 1957 study of how training changes heart rate). Those splits are easy to calculate and they are not anchored to anything that happens inside you.
Two problems follow, and they are why your zones here won't match your watch's.
Your turnpoint isn't at a fixed percentage of your maximum. Where LT2 falls relative to maximum heart rate varies substantially between people, and it moves upward as you get fitter. A fixed 80% band therefore lands in a different metabolic place for different runners, and in a different place for the same runner six months apart. Reviews of intensity prescription make this the central objection to percentage-of-maximum zones: the bands don't correspond to the physiological transitions they claim to describe (Jamnick et al. 2020; Faude et al. 2009).
Maximum heart rate is usually itself a guess. Age-based formulas predict a population average, and individuals scatter widely around it (Tanaka et al. 2001). A zone set as a percentage of an estimated maximum is a percentage of a guess.
Anchoring on thresholds avoids both. LT1 and LT2 are the transitions that actually change what your body is doing, and they move with your training, so the zones move with you. It also matters for how you distribute your training: the well-studied pattern among endurance athletes is a large volume below LT1 and a small volume well above LT2, with comparatively little time in between (Seiler & Kjerland 2006; Seiler 2010). That distribution is only meaningful if you know where your own LT1 and LT2 actually are.
Where your anchors come from
Open Settings → Zones and pick the method that matches what you know. Each one either measures your anchors or estimates them:
| Method | Anchors are | Use it when |
|---|---|---|
| Race result | Estimated | You have a recent race. The most reliable estimate. |
| Predicted race | Estimated | You have no recent race and can judge your shape. |
| Lactate test | Measured | You have step-test data, from a lab or the track. |
| Custom | Yours | You know your boundaries and want to set them. |
From a race. The finish time gives a VDOT — a fitness number derived from the pace-and-distance relationship in Jack Daniels' work. Runtool uses VDOT only to place your anchors: LT2 is estimated near half-marathon effort, LT1 between easy and marathon pace, vVO₂max around 3K effort. The spacing shifts slightly with your training volume, because thresholds sit closer together in higher-mileage runners than in lower-mileage ones.
From a lactate test. Enter the test as steps — pace, heart rate and blood lactate for each one — and pick how the thresholds should be read from the curve:
| Method | How it reads the curve |
|---|---|
| Modified D-max | The largest departure from the straight line through your own curve. The default. |
| Fixed 2 / 4 mmol | The classic fixed lactate concentrations |
| Dickhuth | A fixed rise above your own lactate minimum |
The methods disagree by design — a fixed 4 mmol point assumes everyone's turnpoint sits at the same concentration, which is the assumption individualised methods exist to avoid. You can switch method and see the zones move before saving. If you already know your LT1 and LT2, you can skip the protocol and type them in.
From heart rate alone. If you only know your maximum heart rate, Runtool estimates your threshold heart rate at 92% of it and builds the heart-rate zones from there. It is the weakest input in the system and the easiest to improve — see below.
The starting zones are estimates, and they say so
Runtool always gives you a working set of zones. It has to: you can't train against a blank. But it is worth knowing exactly what those starting numbers are.
- Anchors from a race are interpolated, using relationships fitted across many runners. They are a good first approximation and they do not know your particular physiology.
- Threshold heart rate from maximum heart rate is an estimate of an estimate whenever your maximum is itself age-derived.
- The zone widths are a model. The 10% step below LT1, the midpoint between LT1 and LT2, vVO₂max at roughly 87% of LT2 pace — these are reasonable defaults, not measurements of you.
None of that makes them wrong. It makes them a scaffold. The further your physiology sits from the average — very high or very low mileage, a strong sprint background, a long endurance history, a large gap between your track and road form — the more the defaults will be off, and the more a measurement is worth.
Two measurements pay for themselves quickly:
- A 30-minute time trial replaces your estimated threshold heart rate with a real one. Run 30 minutes as hard as you can hold; your average heart rate over the final 20 minutes is your threshold heart rate.
- A step test, on a track or a treadmill, gives you measured LT1 and LT2 rather than interpolated ones.
Your zones page shows which method produced the set that is currently in force, so you can always see whether you are training against a measurement or an estimate.
Heart rate zones
Heart rate uses Joe Friel's five-zone model, set as percentages of your lactate threshold heart rate (LTHR) rather than of your maximum:
| Zone | Name | % of LTHR |
|---|---|---|
| Z1 | Recovery | under 82 |
| Z2 | Endurance | 82–89 |
| Z3 | Tempo | 89–94 |
| Z4 | Threshold | 94–100 |
| Z5 | VO₂max | above 100 |
Read these as one way of placing the bands once LTHR is known — not as the model itself. The model is still "the boundaries are your thresholds": Z5 opens exactly at LTHR because that is what LTHR is.
A lactate test changes this. It measures LT1 directly, so your measured LT1 heart rate is used as the Z2/Z3 boundary instead of the 89% estimate. Measurements replace estimates rather than being overwritten by them.
Pace stays the primary prescription for running: it responds instantly and doesn't drift. Heart rate tells the effort story behind it — the same pace at a lower heart rate is fitness you can see. The relationship between the two powers the efficiency metrics in Analyse.
Zone definitions are versioned
Zones are versioned, never overwritten. When you update them, the old set is kept with its validity period, and every past workout stays interpreted against the zones that were active when it happened. Your training log never gets rewritten by a fitness change. The Definitions list shows every set you've had, with the method and inputs behind each.
A definition doesn't have to cover both pace and heart rate. Updating just your heart rate zones — after a max HR test, say — saves a heart-rate-only definition, and your pace zones carry on from the definition that set them. Active zones shows what's in force right now, which may come from two different definitions.
Where zones show up
- Workout targets —
8x1km @ Z4resolves to real paces when the workout is created. - Completions — time in zones, rep by rep, planned against executed.
- Analyse — efficiency metrics compare your paces and heart rate against your zones over time.
FAQ
Why don't my zones match my watch's?
Most watches split heart rate by percentage of maximum. Runtool anchors on your lactate thresholds. The two agree only by coincidence, and the gap is usually largest in the middle zones. If you want them closer, set your watch's zones from the boundaries on your Runtool zones page rather than the other way round.How often should I update my zones?
When fitness visibly changes — typically after a race, a fitness test, or a long training block. Zones that are months stale prescribe the wrong paces in both directions.Do I need a lactate test?
No. A recent race result is a solid anchor, and for most runners it is enough. A test is worth it if your race results and your training feel keep disagreeing, if you're returning after a long break, or if you train enough that a few percent of misplaced threshold pace adds up.My max heart rate is a guess. Does that matter?
For pace zones, no — they don't use it. For heart rate zones, yes: they'll be shifted by however far the guess is off. A 30-minute time trial fixes it, and takes one session.Why six pace zones but five heart rate zones?
Above VO₂max effort, heart rate stops discriminating — a 400m repetition and a sprint both max it out. Pace still distinguishes them, so pace gets the sixth zone. Five is also where Friel's model sits, for the same reason.Can I update just my heart rate zones?
Yes. Save a heart-rate-only definition and your pace zones stay exactly as they were — they keep resolving from the definition that set them. The same works the other way round: anchoring pace zones to a new race result leaves your heart rate zones alone.Can my coach change my zones?
Yes — zones belong to the workspace, and both coach and athlete work with the same set. Every change is visible in the definitions list.References
- Daniels, J. (2013). Daniels' Running Formula, 3rd ed. Human Kinetics.
- Faude, O., Kindermann, W. & Meyer, T. (2009). Lactate threshold concepts: how valid are they? Sports Medicine 39(6), 469–490.
- Friel, J. (2009). The Triathlete's Training Bible, 3rd ed. VeloPress.
- Jamnick, N.A., Pettitt, R.W., Granata, C., Pyne, D.B. & Bishop, D.J. (2020). An examination and critique of current methods to determine exercise intensity. Sports Medicine 50(10), 1729–1756.
- Karvonen, M.J., Kentala, E. & Mustala, O. (1957). The effects of training on heart rate: a longitudinal study. Annales Medicinae Experimentalis et Biologiae Fenniae 35, 307–315.
- Seiler, S. (2010). What is best practice for training intensity and duration distribution in endurance athletes? International Journal of Sports Physiology and Performance 5(3), 276–291.
- Seiler, K.S. & Kjerland, G.Ø. (2006). Quantifying training intensity distribution in elite endurance athletes: is there evidence for an "optimal" distribution? Scandinavian Journal of Medicine & Science in Sports 16(1), 49–56.
- Tanaka, H., Monahan, K.D. & Seals, D.R. (2001). Age-predicted maximal heart rate revisited. Journal of the American College of Cardiology 37(1), 153–156.