Running Power: What the Watts on Your Wrist Really Tell You

Cyclists have steered their training by watts for decades — in running, power measurement was long dismissed as a gimmick. Wrongly so: running power is the only metric that shows instantly, honestly across wind and hills, how hard you are actually working. This article explains where the number comes from, how to determine your personal threshold (Critical Power), in which situations watts beat heart rate — and where the limits of the measurement lie.

What is running power — and where does the number come from?

Running power is the mechanical work in watts your body produces while running. Unlike cycling, where a pedal-based power meter measures force directly, running power is estimated: accelerometers in the watch or on your foot capture your movement, a barometer supplies the gradient, GPS the pace — a model combines these with your body weight into produced power. Running 5:00 min/km on flat ground at 70 kg? That corresponds to roughly 240–280 watts, depending on your efficiency.

Three properties make the metric valuable: it responds without delay to every pace change (heart rate needs 30–90 seconds to catch up), it is honest on climbs and into headwinds (watts rise uphill even as pace collapses), and it is independent of your daily condition (heat, caffeine and stress distort heart rate, not mechanical output).

Power vs. heart rate vs. pace: which metric leads when?

None of the three steering metrics is universally best — they answer different questions:

• Pace (min/km): The simplest number, but only comparable on flat, windless ground. Uphill or into a headwind it becomes useless — you look "too slow" while the load is identical.
• Heart rate: Shows the internal load — how dearly the body is paying for the work. Ideal for long, easy sessions and monitoring fatigue. Downsides: lag, cardiac drift on long runs, distortion by heat and stress. Details in our article on heart rate zones.
• Power (watts): Shows the external load — what you actually produce. Ideal for intervals, hills and changing terrain, because the number is instant and terrain-independent.

The practical rule: intervals and hills by power, long endurance runs by heart rate, race splits by pace. Looking at all three together also reveals your training state: if heart rate at the same wattage rises over weeks, fatigue is building; if it falls, fitness is growing. Exactly this combination is what makes the cardiac drift phenomenon interpretable.

Critical Power: your personal threshold in watts

Power zones without a reference are random numbers. The anchor is called Critical Power (CP) — the output you can sustain for roughly 30–60 minutes, the watt equivalent of the anaerobic threshold. Three routes lead there:

• Race method: Your best 5K or 10K result from recent weeks. Average power over 5K typically sits at 105–115 % of CP — most watches and platforms convert this automatically.
• 3/9-minute test: After a warm-up, run 3 minutes all-out, recover easy for 30 minutes, then 9 minutes all-out. CP is derived mathematically from both averages. Brutal, but very accurate.
• Automatic estimation: Garmin, Stryd and others estimate CP continuously from your training data. Convenient, but only as good as the maximal efforts you feed it — if you never run hard, you get a threshold that is too low.

Repeat the test every 6–10 weeks or after training blocks. A stale CP renders all zones useless — the same principle as in power-based cycling training, where FTP does the same job.

Power zones in practice

With a known CP, zones emerge that map onto the classic training intensities. A proven scheme:

• Zone 1 — Recovery (below ~68 % CP): Very easy, active recovery. You feel almost nothing — and that is exactly the point.
• Zone 2 — Endurance (~68–83 % CP): Home of your long, easy runs. Should make up 70–80 % of weekly volume.
• Zone 3 — Tempo (~83–94 % CP): "Comfortably brisk" — classic marathon intensity. Beware: this is where most recreational runners get stuck, training neither truly easy nor truly hard.
• Zone 4 — Threshold (~94–105 % CP): Tempo runs and cruise intervals. More in our article on threshold training.
• Zone 5 — VO2max (~106–120 % CP): Short intervals of 3–8 minutes. This is where power shines most: on the first rep your heart rate still lags far behind while the wattage hits target immediately.
• Zones 6–7 — Anaerobic/sprint (above 120 % CP): Repeats under 3 minutes and strides.

Start conservatively: zones are only trustworthy once your CP comes from a real test or race. In the first weeks, train at the lower edge of each zone rather than the upper.

Managing load: rTSS and the fitness curve

Power makes not just single sessions steerable, but your entire training load. Duration times intensity (relative to CP) produces rTSS (Running Training Stress Score) — one hour at CP equals 100 points. That unlocks the same load logic as heart-rate- or pace-based models: fitness (CTL), fatigue (ATL) and form (TSB) from the relationship between them. We explain the full model in the article on the Training Stress Score. The practical win: a hilly trail run and a flat tempo session finally become comparable in the same currency — watts translate both into work actually done.

Strengths and limits of the wattage

Running power is no substitute for thinking. The key limitations to keep in mind:

• Manufacturer differences: Garmin, Stryd and Coros watts can differ by 10–15 % because each model computes differently (Stryd's foot pod, for instance, ignores wind while wrist-based Garmin includes it). Never compare values across systems — only within the same sensor.
• Body-weight dependency: Gain weight and your wattage at the same pace rises — without you being any fitter. That is why W/kg is the more honest figure.
• Terrain model: On very steep or technical ground (stairs, scree) estimates become inaccurate, because the model assumes smooth running mechanics.
• No fatigue information: Power says what you produce — not what it costs you. A sick body can run the same watts as a fresh one. Combining power with heart rate and feel remains mandatory.

Who benefits most from running power?

Three groups gain the most: interval runners, whose heart rate is too sluggish for short efforts; trail and mountain runners, for whom pace loses all meaning off-road; and race pacers, who want to execute a race around constant external load — especially on hilly courses, where even watts rather than even pace is the more economical strategy. If you mostly run flat and easy, heart rate zones remain excellent — power is an upgrade, not a must. And whichever steering metric you choose: the distribution of intensity matters more than the measurement method, as the 80/20 principle shows.

How Peakora puts your running power into context

Peakora reconciles your sessions through a load model that combines duration, intensity and your individual thresholds — whether the data arrives as pace, heart rate or power. If you own a power-capable watch, the watt values from your activities feed into the TSB form curve; the engine automatically recognises hard and easy days and adjusts the plan in small, controlled steps. You do not need to understand a load model for that — but if you want to, Peakora shows you transparently how every session contributes to your form.

Frequently asked questions about running power

What is running power?

Running power is the mechanical work in watts that you produce while running. Sensors in your watch or on your foot compute it from speed, gradient, acceleration and body weight. Unlike heart rate, the value reacts instantly to every change in pace.

How do I determine my Critical Power?

Easiest via a recent race result (e.g. 5K or 10K), or a structured test: 3 minutes all-out, 30 minutes of easy recovery, then 9 minutes all-out. Critical Power is calculated from both averages and serves as the threshold anchor for your power zones.

Is running power better than heart rate?

Not better, but complementary. Power measures external load instantly and independent of heat, caffeine or stress. Heart rate shows the body's internal response. The ideal setup combines both: power for intensity control, heart rate for fatigue state.

Do I need a separate sensor for running power?

Not necessarily. Many current watches from Garmin, Coros, Polar, Suunto and Apple estimate running power at the wrist. Foot pods like Stryd are considered a more accurate reference because they measure movement at the foot and handle wind more robustly.

What is a good wattage for running?

Absolute watts mean little — what counts is power per kilogram of body weight. As rough guidance at threshold (Critical Power): beginners around 2–3 W/kg, ambitious runners 3–4 W/kg, elite athletes above 5 W/kg.