Steady State

Pace Calculator

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Methodology: all zones anchored to 5K race pace. Z1 65–75%, Z2 76–85%, Z3 86–94%, Z4 95–100%, Z5 101–106%. Z1 HR ceiling = MAF (180 − age). Z2–Z5 HR shown as %HRmax — use as a check only; pace is the primary prescription.
Pace zones & the 5K anchor

All zones are anchored to 5K race pace — a single, measurable reference point that scales correctly across all abilities. The model is based on Seiler's polarised training research.

  • Z1 Easy65–75% of 5K pace
  • Z2 Moderate76–85% of 5K pace
  • Z3 Threshold86–94% of 5K pace
  • Z4 Hard95–100% of 5K pace
  • Z5 VO₂max101–106% of 5K pace

Z1 HR ceiling = MAF. Z2–Z5 prescribed by pace; use HR as a check only.

Stephen Seiler & polarised training

Norwegian exercise scientist Stephen Seiler studied elite endurance athletes across multiple sports and found a consistent pattern: the best performers spent approximately 80% of training time at low intensity and 20% at high intensity — with very little in the middle.

This "polarised" model outperforms threshold-heavy training in research trials, producing greater improvements in VO₂max, lactate threshold, and race performance — particularly for masters athletes where recovery capacity is lower.

Key insight: most recreational runners train too hard on easy days and not hard enough on hard days. The zones in this calculator are designed to enforce that separation.

The 80/20 rule

80% of weekly training volume should be easy (Z1–Z2). 20% hard (Z3–Z5). This distribution is based on Seiler's analysis of elite training logs and has been validated in intervention studies with recreational runners.

  • Z1–Z2 (80%)Easy, long runs, recovery
  • Z3–Z5 (20%)Tempo, intervals, race efforts

For masters runners, erring toward 85/15 is prudent — recovery capacity declines with age.

Why Z1 & Z2 matter

Easy running is where the foundational adaptations happen. Training at Z1–Z2 stimulates mitochondrial density — increasing the number and efficiency of the cells' energy-producing units. More mitochondria means more aerobic capacity at every intensity.

Z1–Z2 also develops a denser capillary network around muscle fibres, improving oxygen delivery and waste removal. These adaptations are slow-build — they accumulate over months, not weeks — and they cannot be rushed by training harder.

For masters runners specifically: aerobic base work carries the lowest injury and recovery cost. The athletes who improve most consistently are almost always the ones who protect their easy days.

Race predictions — Riegel

Predicted times use the Riegel formula: T₂ = T₁ × (D₂/D₁)1.06. The 1.06 exponent accounts for endurance decay across distances.

  • 10K from 5K×2.085
  • HM from 5K×4.60
  • Marathon from 5K×9.59

Marathon will overshoot for athletes without a long-run base. Treat predictions as ranges, not promises.

MAF — the Z1 HR ceiling

MAF = 180 − age (Maffetone). For masters runners, MAF defines the Z1 HR ceiling — overriding the standard %HRmax bound used by Z2–Z5.

Rationale: at age 40+, the 75% HRmax ceiling often pushes athletes above true aerobic threshold. MAF is more conservative and protects easy days. For athletes 55+, cross-check with talk test and nose-breathing.

If MAF feels too restrictive — use the 30-minute field test below to find the athlete's actual aerobic threshold HR instead of relying on the formula.

Key terms — LT1, LT2, vVO₂max, MAF
  • LT1 — Lactate Threshold 1The pace at which lactate begins accumulating above resting levels. Below LT1 = fully aerobic. Upper boundary of Z2.
  • LT2 — Lactate Threshold 2The pace at which lactate accumulates faster than it clears. Sustainable for ~60 min in trained athletes. Z3 sits around this point.
  • vVO₂maxThe minimum pace that elicits maximum oxygen uptake. For recreational runners, approximately equal to 5K race pace. Defines Z5.
  • MAF — Maximum Aerobic FunctionHR ceiling for Z1, calculated as 180 − age (Maffetone). If HR exceeds MAF on an easy run, the pace is too fast.
HR vs pace prescription

Pace is the primary prescription. HR lags pace by 60–90s at Z4/Z5, drifts in heat, and is suppressed by fatigue. Use HR to govern easy runs; use pace to govern intervals.

The Tanaka formula (208 − 0.7 × age) has a ±10–12 bpm error. For accurate HR zone prescription, field test it and enter the result in Tested HRmax.

Hill repeat HRmax test

The safest field method for finding true HRmax:

  1. Find a 600m hill, moderate gradient
  2. 15 min easy warm-up + 4–6 strides
  3. 3–4 hard reps up, jog down for recovery
  4. Final rep: sprint flat-out for last 200m
  5. Peak HR 30s after stopping = HRmax
  6. Chest strap mandatory — wrist optical underreads
30-minute aerobic threshold test

Use when the MAF formula feels too restrictive:

  1. Flat, measured course (track ideal). Chest strap mandatory.
  2. 15 min easy warm-up — HR well below MAF before starting.
  3. Run 30 mins at the fastest pace you can sustain while still passing the talk test throughout — short sentences just possible, never breathless.
  4. Record average HR over the final 20 minutes only. That HR = your aerobic threshold ceiling.
  5. Record average pace for the full 30 minutes. That pace = your aerobic training pace.
  6. Enter the result in the MAF HR field to override the formula.
  7. Retest every 6–8 weeks — same HR, faster pace = aerobic base developing.

Evidence base: East Carolina University (2005) found the 30-minute time trial was the only field test whose estimated lactate threshold HR did not significantly differ from blood-draw lab results — outperforming the Conconi test and formula-based methods.

Before testing: 4+ weeks consistent base, no recent illness, no injury. Cardiac risk factors → GP clearance first. Retest every 12–18 months.