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Marathon Pacing by Heart Rate & RPE (and Why HR Drifts Upward)

Updated: · Reading time: ~12–16 min

GPS pace lies. Weather changes. Adrenaline makes “too fast” feel easy. Heart rate and RPE (rate of perceived exertion) help you pace the marathon like a grown-up: controlled early, steady middle, brave late.

This guide shows you how to use HR + RPE in practice, and why heart rate drifts upward even when you run the same pace.

How to use this guide

This page is not about replacing pace with a wrist number. It is about using internal signals to stop small pacing errors from becoming race-day damage. At MarathonPaceKM, the practical approach is hybrid: pace gives you the external plan, while HR and RPE tell you whether the cost of that plan is still sustainable.

Why HR + RPE are useful for marathon pacing

Pace is external. Heart rate and RPE are internal. The marathon is long enough that internal cost matters more than early pace precision. Research in marathoners has linked pacing strategy to cardiac drift and performance, and “cardiac cost” has been used to describe how the internal cost of the same pace changes during a marathon.

HR is not perfect, and RPE is subjective. But together they give you a reliable effort dashboard when GPS, tangents, crowds, and weather make pace alone less trustworthy.

This is also where controlled marathon training pays off. If you use a system like Norwegian Singles for marathon training, one benefit is that you get better at recognising the difference between controlled work and disguised overpacing.

What RPE is (and how to use it)

RPE (rating of perceived exertion) is a simple way to score how hard the work feels. The classic Borg scale runs from 6 to 20 and was designed to roughly correlate with heart rate in broad terms. Many studies show RPE tracks well with physiological markers like heart rate and lactate.

RPE (0–10) What it feels like Talk test Where it fits in marathon day
3–4 Easy / relaxed Full sentences Warm-up, early settling, easy kilometres
5 Steady / all-day feel Short sentences Early marathon once settled in cool conditions
6 Controlled work Short phrases Typical marathon effort mid-race
7 Hard but manageable 1–3 words Late marathon if pacing and fueling are good
8+ Very hard / survival Not really Final push only

Why heart rate drifts upward (even at the same pace)

During prolonged exercise, many runners see HR slowly creep upward even while pace stays steady. This is commonly described as cardiovascular drift. Reviews describe the pattern as a time-dependent rise in HR alongside declines in stroke volume and mean arterial pressure during prolonged work.

The main drivers of HR drift

  • Heat stress: as skin and core temperature rise, cardiovascular demands shift and heart rate rises.
  • Dehydration and reduced plasma volume: fluid loss can reduce stroke volume, especially in the heat.
  • Reduced filling time at higher HR: as HR rises, filling time shortens, which can reduce stroke volume further.
  • Neuromuscular fatigue: as mechanics degrade, the same pace can become more expensive.

For the humidity-specific version of this problem, use Dew Point Pacing Guide.

The best approach: hybrid pacing (pace + HR cap + RPE)

Here is the simplest way to think about it:

When Primary guide Secondary guide Why
0–10K HR cap RPE + pace cap Adrenaline and crowds make pace feel easy; HR cap prevents early debt
10–30K Pace (if conditions stable) RPE Settle into sustainable rhythm; keep effort honest
30–42K RPE HR + pace Late drift and fatigue make HR less actionable; RPE tells you what is still sustainable

A race-day HR & RPE script (0–42.2K)

This is a doable script, not a perfect physiological model. The key is restraint early and patience mid-race. If you want the pace-first version for the opening, pair this with How to pace the first 10K.

0–3K: settle

  • RPE: 4–5 (controlled, relaxed)
  • Rule: no surges, no weaving, no urgency
  • HR: ignore the first few minutes; HR response lags

3–10K: the HR cap window

  • RPE: 5–6 (short phrases OK)
  • HR: hold under your planned early cap
  • Pace: allow a slight float on hills and headwinds

10–30K: lock in

  • RPE: 6 (steady focus)
  • Pace: target goal MP when conditions are stable
  • HR: expect gradual drift; do not panic-slow unless RPE is rising too
  • Fuel: stay on schedule

30–42K: race by RPE

  • RPE: 6.5 → 7.5 depending on the day
  • HR: use it as a warning sign, not a steering wheel
  • Pace: let pace reflect durability, conditions, and fueling success

For the decision version of this, see When to Adjust Marathon Pace Mid-Race.

How to set your HR targets without a lab test

The goal is not a magical HR number. The goal is a cap that keeps you honest early and supports even pacing.

Step 1: Get an accurate goal pace

Use the predictor plus your recent races, then convert to MP with the pace calculator. If it is hot or windy, adjust with the conditions tool.

Step 2: Find your marathon HR range in training

In a long run with marathon-pace blocks, note the HR you can hold while: (a) breathing stays controlled, (b) mechanics stay clean, (c) fueling works.

  • Example session: 2 × 6 km @ MP inside a long run
  • Record: average HR for each block + RPE start/end + drift pattern

Step 3: Set a conservative HR cap for the first 10K

Your early cap should be below the HR you held during MP blocks late in long runs. The point is restraint, not precision theatre.

How to train HR + RPE pacing in long runs

Workout 1: HR-capped easy long run

  • Run easy and keep HR under an easy cap
  • Observe drift: does HR creep up? does pace fall?
  • Practice fueling if the run is longer than 90 minutes

Workout 2: MP blocks with RPE notes

  • Example: 28–34 km total with 2 × 6 km @ MP (2 km easy between)
  • Write down RPE at start and end of each block
  • Goal: stable pacing + controlled breathing, not fast for Strava

Workout 3: Progression long run by RPE

  • Start easy (RPE 4)
  • Move to steady (RPE 5)
  • Finish controlled (RPE 6), optionally near MP if the day is good

If you want to compare controlled threshold systems with steadier traditional marathon work, see Norwegian Singles vs Tempo Runs.

Common mistakes (and fixes)

  1. Chasing HR in the first 2K.
    Fix: HR lags. Use RPE + a pace cap early; use HR cap only after you settle.
  2. Using HR as the only steering wheel late.
    Fix: drift is expected. Late-race pace should be driven by RPE + mechanics + fueling success.
  3. Ignoring conditions.
    Fix: in heat, wind, or hills, anchor by RPE and let pace float; use the conditions adjuster.
  4. Turning every long run into steady work.
    Fix: alternate easy long runs with specific long runs. Keep easy days easy.
  5. Fueling too late.
    Fix: practice fueling early and consistently; do not wait for the crash.

If you have a habit of pushing too hard too often, read Who Should Not Do Norwegian Singles.

FAQ

Why does my heart rate drift upward at the same pace?

Cardiovascular drift during prolonged exercise often includes a gradual decline in stroke volume and mean arterial pressure with a compensatory rise in HR. Heat stress and dehydration can amplify this effect.

Should I pace my marathon by heart rate or pace?

Hybrid works best: pace targets for stable conditions, but HR caps + RPE to prevent early overpacing and to adjust for conditions.

What RPE should a marathon feel like?

Early: controlled. Mid: steady focus. Late: hard but manageable if pacing and fueling are right. If it feels like threshold early, you are going too fast or conditions are harsh.

Can I use heart rate as a ceiling in the first 10K?

Yes. This is one of the simplest ways to avoid the easy-early trap that leads to late slowdown.

How do I set my marathon HR without a lab test?

Practice marathon-pace blocks in long runs and note the HR you can hold with controlled breathing, stable mechanics, and successful fueling. Use that to set a conservative early cap on race day.

Related tools & guides

About MarathonPaceKM

MarathonPaceKM publishes practical pacing tools, calculators, and training guides designed to help runners make better decisions from race data, pacing logic, recovery context, and real-world training feedback.

Learn more on the About page, get in touch via Contact, and read the Disclaimer and Privacy Policy.

Related pages: Marathon Pace Calculator · Race-Day Pace Adjuster · Norwegian Singles · Norwegian Singles for marathon training

References

  1. Souissi A, et al. (2021). A new perspective on cardiovascular drift during prolonged exercise. PubMed
  2. Coyle EF. (1998). Cardiovascular drift during prolonged exercise and the effects of dehydration. PubMed
  3. Coyle EF. (2001). Cardiovascular drift during prolonged exercise: new perspectives. PubMed
  4. Billat VL, et al. (2020). Pacing strategy affects the sub-elite marathoner’s cardiac drift and performance. PMC
  5. Takayama F, et al. (2025). Do heart rates of elite marathon runners exhibit room for drift? Implications for durability. PMC
  6. Scherr J, et al. (2013). Associations between Borg’s RPE and physiological measures. PubMed
  7. Williams N. (2017). The Borg Rating of Perceived Exertion scale. OUP

Educational content only. Adjust pacing for your history, health, recovery, and race-day conditions.