Intensity

There are several ways to say how hard a run should be. You can name a zone (Z4), an effort (tempo), an RPE (RPE 7), or a threshold (LT2). They are four ways of saying the same thing, and this page is where they are defined against each other.

Every one of them works in workout notation, in the pace picker, and in what Runtool writes back to you. Effort ratings you log after a session read from the same table, so the 7 you tap and the intensity your run is priced at are the same number.

The table#

Read the two boundaries that matter off the RPE column: LT1 sits between RPE 4 and 5, and LT2 sits between RPE 7 and 8. Those are your aerobic threshold and your lactate turnpoint. See Zones for what they are and where yours come from.

A rating on a boundary belongs to the zone above it. An RPE of 5 is the first rating above LT1, so it is Z3.

Easy is Z1, steady is Z2#

easy names Z1 and steady names Z2. This surprises people who expect easy running to be Z2, so it is worth saying why.

Your Z1/Z2 line sits 10% slower than LT1. For a runner with LT1 at 5:00/km that line is at 5:30/km, which puts Z2 in a narrow band from 5:00 to 5:30. Most easy running is slower than that. Z2 is the top of easy running, close enough to LT1 to be noticeably steadier, and Z1 is where the everyday run actually lands.

A run with no effort written at all stays at Z2. 10km and 10km easy are different instructions: the first leaves the pace open, the second asks for an easy run.

RPE#

RPE is rating of perceived exertion, how hard the session felt, from 1 to 10 Borg, 1982. You log it against a completed workout, and you can also prescribe with it: 45min @ RPE 3 is a run you want run easily, without naming a pace. A band works too: 75min @ RPE 6-7.

Write the word either side of the number: @ RPE 3 and @ 3rpe are the same instruction. A bare @ 3 is not accepted, because it could be a pace or a rep count.

A prescribed rating stays a rating. The segment reads back as RPE 7, not as the zone it sits in and not as a pace, because on trail, in hills or in heat the pace that effort produces is not the pace that effort produces anywhere else. It is also the one target that needs no zones at all: 45min @ RPE 3 is a complete instruction before you have entered a single zone boundary.

An RPE and a duration are enough to price a session's training load on their own, which is what makes it worth logging even when you have no watch data. The zone the rating names is the zone the load model uses. That holds for a prescribed rating as much as a logged one, so an RPE session still projects a load, a duration and a place in your zone distribution.

Where the numbers come from#

The mapping is measured, not chosen.

Runners in a lab. A study of 95 moderately trained runners recorded RPE against blood lactate through a treadmill step test Dantas et al., 2015. It puts the 2 mmol/L boundary at RPE 4.3 and the 4 mmol/L boundary at RPE 6.5. Those two concentrations are the classic stand-ins for LT1 and LT2.

Olympiatoppen's intensity scale. The Norwegian Olympic Federation publishes a five-zone scale with a Borg CR-10 anchor for each zone: 1–2, 2–3, 4–5, 6–7, 8–10. Its zone splits line up with Runtool's in pairs, because both are built on the same two thresholds. It is a federation document rather than a paper, so it is named here rather than cited; the peer-reviewed work establishing the framework it belongs to is Seiler-Viken et al., 2025.

Both put LT1 near RPE 4 to 5 and LT2 near RPE 6.5 to 7. Runtool places LT1 on the 4/5 line and LT2 on the 7/8 line. LT1 lands inside the measured confidence interval. LT2 sits half a point above it, on purpose: you rate a session after it ends, and a whole-session rating of a given intensity runs a little higher than a rating taken mid-test Foster et al., 2001.

Your own scale will not match a study exactly. Use the table as the shared meaning of the numbers, not as a claim about your physiology.

Prescribing at a threshold#

A zone is a band. 20min @ Z4 means anywhere in Z4, and Runtool targets the middle of the band, which sits between LT1 and LT2. That is usually what you want for reps.

When you mean the threshold itself, name it:

These are single paces, not ranges, and they are read straight off your zone boundaries. So 2x20min @ LT1 / 2min is sub-threshold work at your LT1, and 20min @ LT2 is threshold work at your turnpoint, not at the middle of the Z4 band.

They move when your zones move. Set new zones after a race and every workout written this way retargets with them.

threshold still means the Z4 band, so nothing you have already written changes meaning.

Renaming a zone#

If your coaching vocabulary differs, change the names. Open Settings → Zones and put your word in the Zone names field for any zone. Leave one empty to keep the standard name.

The name is used everywhere: workout titles, zone readouts, the pace picker, and what the Runtool Agent says. It also becomes a word notation accepts, so renaming Z3 to Sub-threshold lets you write:

4x8min @ sub-threshold / 2min

Two rules apply:

• Standard words keep their meaning. Naming Z5 Tempo does not make tempo mean Z5. tempo is still Z3, and Tempo is what Z5 is called on screen.
• A name has to start with a letter. A zone called 5K pace is shown everywhere but is not a word notation reads, because it would collide with the 5 in 5x1km.

FAQ#

Why does my easy run price lower than it used to?

`easy` names Z1 now, and Z1 is priced lower per minute than Z2. This changes new workouts as you write them; workouts you already saved keep the zone they were saved with. If you want the old target, write `steady` or `Z2`.

Is RPE the same scale my coach uses?

Probably close. Runtool uses 1 to 10, which is the shape of the Borg CR-10 scale [Borg, 1982](https://doi.org/10.1249/00005768-198205000-00012). If your coach uses the 6 to 20 Borg scale, the numbers are different but the anchors are the same: their 13 to 14 is around our 5 to 6.

Can I rate an interval session with one number?

Yes, and that is what the field is for. It is a whole-session rating, so rate how the session felt overall rather than how the hardest rep felt. A session of 10x400m does not rate 10 because the reps were maximal.

What about marathon pace and 10K pace?

Not yet. Race paces come from a VDOT, and a zone set built from a lactate test or entered by hand does not carry one, so there is no honest answer for every athlete. Use an absolute pace (`@ 4:30`) or a percentage of threshold in the pace picker.

Does renaming a zone change any of my data?

No. Renaming changes what a zone is called, not where its boundaries sit or what any workout targets.

References#

• Borg, G.A.V. (1982). Psychophysical bases of perceived exertion. Medicine & Science in Sports & Exercise 14(5), 377–381. 10.1249/00005768-198205000-00012
• Dantas, J.L., Doria, C., Rossi, H., Rosa, G., Pietrangelo, T., Fanò-Illic, G. & Nakamura, F.Y. (2015). Determination of blood lactate training zone boundaries with rating of perceived exertion in runners. Journal of Strength and Conditioning Research 29(2), 315–320. 10.1519/JSC.0000000000000639
• Foster, C., Florhaug, J.A., Franklin, J., Gottschall, L., Hrovatin, L.A., Parker, S., Doleshal, P. & Dodge, C. (2001). A new approach to monitoring exercise training. Journal of Strength and Conditioning Research 15(1), 109–115. 10.1519/00124278-200102000-00019
• Seiler-Viken, S.A., Mentzoni, F., Seiler, S., Skarli, S. & Losnegard, T. (2025). Contextualizing the Norwegian standardized intensity zone framework in an international sample of endurance practitioners. Scientific Reports 15, 34367. 10.1038/s41598-025-17023-z