RecovHR — Know When to Go Again

The Problem

Two Ways to Fail

Too Little Rest

Too Soon

PCr only ~50% restored. Session quality collapses by rep 4.

3–4 reps

before quality collapse

Too Much Rest

Too Late

45–75s wasted re-ramping to target intensity per rep.

45–75s

wasted per rep in an 8-rep session

🎯

RecovHR finds the window. One number per rep: the exact HR where you're recovered enough to go hard — without losing training stimulus.

The Algorithm

Heart Rate Reserve

HR_max

Maximum Heart Rate

Measured, or Tanaka formula: 208 − (0.7 × age).

HR_rest

Resting Heart Rate

Morning seated. Two runners at the same HRmax can differ 30 bpm here.

LTHR

Lactate Threshold HR

30-min time trial, avg HR of final 20 min. Or estimate: 87% × HRmax.

Age

Only needed when HRmax is not directly measured.

Algorithm Dashboard · HRmax 188 · HRrest 48 · HRR 140

188

HR_max

−

HR_rest

→

140

HRR

usable range

0.42

fraction
(VO2max)

HR_rest

→

107

bpm · start next rep

Step 01

HRR = HR_max − HR_rest

Your usable cardiac range. All thresholds scale from this.

Step 02

T = (HRR × f) + HR_rest

f = 0.42 VO2max · 0.50 LT · 0.35 Speed · 0.38 Easy.

Step 03 — Drift

T_adj = T + (n−1) × 1.5

From rep 3 onward. Corrects for +1–2 bpm/rep cardiac drift.

Workout Types

Four Thresholds.

Each workout type produces distinct physiological stress. RecovHR applies different HRR fractions so recovery matches the actual demand.

VO2MAX

90–100% HRmax · 3–5 min reps

Start when HR ≤

107 bpm

HRR fraction: 0.42

Min rest: 90 seconds

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

400m–1600m repeats · 5K effort

88–97% LTHR · 8–20 min reps

Start when HR ≤

118 bpm

HRR fraction: 0.50

Min rest: 60 seconds

HR didn't peak — less recovery needed. Partial rest preserves the lactate signal.

Tempo intervals · cruise intervals

Speed

Max effort · sub-30s reps

Start when HR ≤

97 bpm

HRR fraction: 0.35

Min rest: 120 seconds

HR lags 30–60s. Clock floor is primary (93% PCr). HR is confirmation only.

Strides · hill sprints · 100–200m

Easy

65–78% HRmax · aerobic effort

Start when HR ≤

101 bpm

HRR fraction: 0.38

Min rest: 30 seconds

Primary use: monitoring the work interval, preventing surges into threshold territory.

Aerobic fartlek · relaxed surges

Session Plan

8×400m VO2max · HRmax 188 · HRrest 48

Rep	Base	Drift	Start when HR ≤	Min rest
1	107	—	107	90s
2	107	—	107	90s
3	107	+3.0	110	90s
4	107	+4.5	112	90s
5	107	+6.0	113	90s
6	107	+7.5	115	90s
7	107	+9.0	116	90s
8	107	+10.5	118	90s

Drift correction saves ≈45–75s per late rep — preserving late-session training stimulus.

The Science

Why These Numbers

The Recovery Curve

90–140s Sweet Spot Window

RecovHR targets the exact zone where HR has dropped enough to go hard again — without losing the training stimulus from 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.

Why Not % HRmax?

21 bpm Difference at 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). But the Karvonen formula gives 101 bpm vs. 122 bpm — a 21-bpm spread that reflects their very different physiological readiness states.

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 (PCr) is the immediate fuel for maximal efforts. It has 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 resynthesis milestones — preventing any rep from starting before the fuel system is ready.

Cardiac Drift

+1.5 bpm Per Rep from Rep 3

A fixed threshold gets harder to meet as the session progresses. 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 due to thermoregulation and dehydration (Rampinini et al., 2015). Without correction, rep 8 with a fixed threshold demands 45–75 extra seconds — systematically diluting late-session training stimulus. RecovHR adds 1.5 bpm/rep from rep 3 onward to preserve identical readiness across the full 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 to individual usable cardiac range.

Karvonen et al., 1957

VO2max HRR Fraction (0.42)

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

Helgerud et al., 2007 · Buchheit & Laursen, 2013

PCr Resynthesis Kinetics

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

Harris et al., 1976 · Glaister, 2005

Drift Constant (1.5 bpm/rep)

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

Rampinini et al., 2015

Tanaka HRmax Estimate

208 − 0.7 × age. Lower error than 220 − age across adults.

Tanaka et al., 2001

Limitations

HR lags sprints

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

Drift is a mean

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

LTHR variance

87% × HRmax spans 80–92% in literature. Field test preferred.

No RCT yet

Not tested in a controlled trial vs. clock-gated recovery.

References

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.