RecovHR

Heart-rate reserve · interval recovery · 2026

Know when to go again.

Between hard reps, most runners guess. RecovHR converts four biometrics into one number per rep — the heart rate at which you're recovered enough to go hard again.

Find your number Read the paper ↗
Recovery · VO2max rep t+0s
172bpm
recoveringthreshold 107 bpm · HRmax 188 · HRrest 48

The problem

Two ways to waste a workout

Recovery between reps is the least-measured variable in interval training. Getting it wrong in either direction has a cost.

3–4 reps

Go too soon

With phosphocreatine only ~50% restored, session quality collapses by the fourth rep. You finish the workout without getting the workout.

45–75 s / rep

Wait too long

Fully reset between reps and you spend 45–75 extra seconds re-ramping to target intensity — diluting the training stimulus you came for.

RecovHR finds the window. One number per rep: the exact heart rate where you're recovered enough to go hard, without losing the stimulus of incomplete rest.

The algorithm

Four inputs. One formula.

Every threshold scales from heart-rate reserve — your usable cardiac range — so the same session prescribes different numbers for different athletes.

HRmax

Maximum heart rate

Measured, or estimated by the Tanaka formula: 208 − 0.7 × age.

HRrest

Resting heart rate

Morning, seated. Two runners with the same HRmax can differ by 30 bpm here.

LTHR

Lactate threshold HR

30-minute time trial, average HR of the final 20 minutes. Or estimate: 87% of HRmax.

Age

Age

Only needed when HRmax is not directly measured.

Worked example HRmax 188 · HRrest 48 · VO2max session
Reserveusable cardiac range
HRR = HRmax − HRrest = 188 − 48
140 bpm
Thresholdf = 0.42 for VO2max · 0.50 LT · 0.35 speed · 0.38 easy
T = HRR × f + HRrest = 140 × 0.42 + 48
107 bpm
Drift+1.5 bpm per rep, from rep 3
T(n) = T + (n − 1) × 1.5  →  rep 6
114 bpm

Try it

Your thresholds

Enter two numbers. Results update as you type.

Measured max. Leave blank to use age.

Morning seated heart rate.

Tanaka estimate: 208 − 0.7 × age.

Drift correction applies from rep 3.

VO2max

—
bpm · min rest 90s

LT

—
bpm · min rest 60s

Speed

—
bpm · min rest 120s

Easy

—
bpm · min rest 30s

Workout types

Four efforts, four thresholds

Each workout type produces distinct physiological stress, so RecovHR applies a different HRR fraction to each — recovery matched to actual demand.

VO2max
90–100% HRmax · 3–5 min reps
Start when HR ≤
107 bpm
f = 0.42
min rest 90s

Incomplete recovery preserves elevated cardiac stress. Matches the 4×4 Norwegian protocol.

400m–1600m repeats · 5K effort

LT
88–97% LTHR · 8–20 min reps
Start when HR ≤
118 bpm
f = 0.50
min rest 60s

HR didn't peak, so less recovery is needed. Partial rest preserves the lactate signal.

Tempo intervals · cruise intervals

Speed
Max effort · sub-30s reps
Start when HR ≤
97 bpm
f = 0.35
min rest 120s

HR lags 30–60s behind a sprint. The clock floor governs; HR is confirmation only.

Strides · hill sprints · 100–200m

Easy
65–78% HRmax · aerobic effort
Start when HR ≤
101 bpm
f = 0.38
min rest 30s

Primarily a monitor for the work interval — preventing surges into threshold territory.

Aerobic fartlek · relaxed surges

Session plan 8 × 400m VO2max · HRmax 188 · HRrest 48
RepBaseDriftStart when HR ≤Min rest
1107—10790s
2107—10790s
3107+3.011090s
4107+4.511290s
5107+6.011390s
6107+7.511590s
7107+9.011690s
8107+10.511890s
Drift correction saves ≈45–75s per late rep, preserving late-session training stimulus.

The science

Why these numbers

Heart rate recovery curve with RecovHR thresholds

The recovery curve

90–140s
Sweet-spot window

RecovHR targets the zone where HR has dropped enough to go hard again — without losing the training stimulus of incomplete rest.

Learn more
After a hard effort, HR decays exponentially. The fast phase (~30s) is parasympathetic reactivation; the slow phase (30s–3 min) is sympathetic withdrawal. The shaded region in the chart marks the window: past the point where cardiovascular stress has dropped, but before complete autonomic reset dilutes the training signal.
Karvonen formula versus percent of HRmax

Why not %HRmax?

21 bpm
Spread at the same HRmax

Two athletes, same HRmax — but resting HR differs by 30 bpm. Karvonen corrects for that. A fixed %HRmax ignores it entirely.

Learn more
At HRmax 188 with HRrests of 38 vs. 68, the "65% HRmax" recovery target is identical for both athletes (122 bpm). The Karvonen formula instead gives 101 vs. 122 bpm — a 21-bpm spread reflecting genuinely different readiness states.
Phosphocreatine resynthesis kinetics

The clock floors

90s = 87%
PCr restored

No matter how fast HR drops, the fuel must be physically ready. Clock floors enforce the PCr resynthesis timeline.

Learn more
Phosphocreatine — the immediate fuel for maximal efforts — resynthesizes with a half-life of ~30s (Harris et al., 1976). At 90s, 87% is restored; at 120s, 93%. The VO2max floor (90s) and speed floor (120s) are pinned to these milestones so no rep starts before the fuel system is ready.
Cardiac drift across an interval session

Cardiac drift

+1.5 bpm
Per rep, from rep 3

A fixed threshold gets harder to meet as the session goes on. RecovHR adjusts each rep to match actual cardiac drift.

Learn more
In a multi-rep session, end-of-recovery HR rises 1–2 bpm per rep from thermoregulation and dehydration (Rampinini et al., 2015). Uncorrected, rep 8 demands 45–75 extra seconds against a fixed threshold. RecovHR adds 1.5 bpm/rep from rep 3 onward to hold readiness constant across the session.

Method

Index construction

Every parameter — HRR fraction, drift constant, clock floor — has a named source. No proprietary data, no black box.

Karvonen HRR formula

Foundation of all thresholds. Scales targets to individual usable cardiac range.

Karvonen et al., 1957

VO2max fraction · 0.42

From the 4×4 Norwegian protocol's 70% HRmax active-recovery bound, converted to HRR.

Helgerud 2007 · Buchheit & Laursen 2013

PCr resynthesis kinetics

τ ≈ 43.7s. Basis for clock floors — 87% restored at 90s, 93% at 120s.

Harris 1976 · Glaister 2005

Drift constant · 1.5 bpm/rep

Empirical mean from a middle-distance interval study. Applied from rep 3.

Rampinini et al., 2015

Tanaka HRmax estimate

208 − 0.7 × age. Lower error than 220 − age across adult populations.

Tanaka et al., 2001

Known limitations

HR lags sprints

HR peaks 30–60s after a sub-30s rep. The clock floor governs; HR is confirmation.

Drift is a mean

1.5 bpm/rep comes from one study. Heat can push it to 2–3 bpm/rep.

LTHR variance

The 87% × HRmax estimate spans 80–92% in the literature. A field test is preferred.

No RCT yet

Not yet tested in a controlled trial against clock-gated recovery.

References

Full bibliography
  • Buchheit & Laursen — HIIT programming puzzle. Sports Medicine 2013.
  • Cole et al. — Heart-rate recovery and mortality. NEJM 1999.
  • Glaister — Multiple sprint work physiology. Sports Medicine 2005.
  • Harris et al. — PCr resynthesis time course. Pflügers Archiv 1976.
  • Helgerud et al. — Aerobic intervals improve VO2max. MSSE 2007.
  • Karvonen et al. — Training effects on heart rate. Ann Med Exp Biol Fenn 1957.
  • Menzies et al. — Lactate clearance and recovery intensity. J Sports Sci 2010.
  • Rampinini et al. — HR during interval recovery. JSSM 2015.
  • Tanaka et al. — Age-predicted maximal heart rate. JACC 2001.