Running Pace and Heart-Rate Zones: Setting Training Intensity

Pace = time ÷ distance; speed = distance ÷ time. 10 km in 50 minutes → pace 5:00/km, speed 12 km/h.

Reverse from a goal: a 1:45 half marathon → 105 ÷ 21.0975 ≈ 4:59/km. A half is 21.0975 km, not 21 — the wrong distance makes the target pace too aggressive.

Estimate max HR with 220 − age (±10 bpm), then use Karvonen for heart-rate reserve:

Age 30, resting HR 60: max 190, reserve = 190 − 60 = 130.
At 60% → 60 + 130 × 0.6 = 138; at 80% → 60 + 130 × 0.8 = 164. Target 138–164 bpm.

Karvonen is more individual than a plain percentage of max HR because it accounts for resting HR.

A common endurance split is ~80% low intensity (full conversation, lower end of the zone) and ~20% moderate-to-hard (tempo, intervals).

The classic beginner mistake is running every session at a "moderately hard" middle effort — too hard to build aerobic base, too easy to develop speed, and fatiguing on top. Simple test: if you can chat on an easy run, it is easy enough.

Heart rate creeping up at a constant pace is cardiac drift, common in heat, dehydration or the later stages of a long run. Slow down based on heart rate or effort rather than forcing the pace.

Other factors: poor sleep, caffeine, stress, hills, headwind and a recent meal. Compare sessions under similar conditions and read the trend, not a single absolute number.

• Running at race pace every time: the main source of injury and burnout.
• Treating a formula max HR as exact: individual variation is large and medication changes it; use a graded exercise test when precision matters.
• Ignoring recovery: fitness is built during recovery — one hard day and two easy days beat consecutive hard days.

With cardiovascular disease, chest pain, unusual breathlessness or heart-rate medication, consult a clinician before setting intensity.