You slow down to what feels like a shuffle. Your breathing is fine. And your watch still says 165.
It’s one of the most common questions new runners ask, usually right after someone tells them to “run in zone 2”. The good news: in most cases there’s an ordinary explanation, and it gets better with time. Here are the usual suspects, roughly from most to least common.
1. Your “slow” isn’t easy for you yet
Pace is relative. If you started running a few months ago, your aerobic system is still catching up with your legs and your motivation. A pace that is slow compared with other people can still be moderate or even hard for you.
That’s not a flaw. It’s where everyone starts. The heart, the small blood vessels in your muscles and the muscles’ ability to use oxygen all adapt to easy running, but over weeks and months, not days.
What to do: slow down further, even if that means a very slow jog. If that’s still too much, add walk breaks: one minute of running, one minute of walking is a perfectly good zone 2 session. Walking the hills is allowed too.
2. The formula doesn’t fit you
Most watches and apps start from an estimate of your maximum heart rate, and then set the zones as percentages of it. The estimates are averages. Real people scatter around them, and many are off by ten beats or more.
If your true maximum is higher than the formula says, every zone the app shows you is too low. Your “zone 3” might be your real zone 2.
iRunning estimates your max from your age and sex. It uses 220 − age for men, 206 − 0.88 × age for women, and 208 − 0.7 × age otherwise. Zone 2 is 60–70% of that number. For a 40-year-old man that’s a max of 180 and a zone 2 of 108–126 bpm, which is low for a lot of fit 40-year-olds.
What to do:
- Use the talk test as a cross-check. If you can speak in full sentences at “zone 3”, your zones are probably set too low.
- Enter your real max if you know it. Maybe from a lab test, or the highest reading from a hard race finish with a chest strap. In iRunning: Settings › Heart rate zones. You can pick any max from 120 to 220, and the zones rescale. You can also drag each zone boundary yourself.
- Don’t go chasing your max to find out. A hard all-out test isn’t a good idea if you’re new to running or have a health condition.
3. Heat, sleep, caffeine and stress
Your heart rate at a given pace isn’t fixed. It moves with the conditions:
- Heat and humidity. Your body sends more blood to the skin to cool you, so your heart beats faster to keep up.
- Poor sleep, a stressful day, or a cold coming on. All of them can push your heart rate up at the same effort.
- Caffeine shortly before a run.
- Not enough fluid, especially on warm days.
What to do: judge by effort on those days, not by the number. A run that’s 10 beats higher than last week’s in 25 °C isn’t a step backwards.
4. Drift: the second half runs higher
Run at a steady pace for 40 minutes or more and your heart rate usually creeps up, even though you haven’t sped up. This is called cardiac drift. It’s more noticeable in the heat and when you haven’t had enough to drink.
What to do: start slower than feels right, so there’s room for the drift later. On a long run it’s fine to slow down, or walk for a minute, when the heart rate climbs.
5. The sensor is guessing
Optical sensors on the wrist are good at steady efforts, but they have known weak spots:
- The first few minutes. Readings can jump around before they settle.
- A loose fit. Light gets in and the reading gets noisy. Wear the watch snug, a finger’s width above the wrist bone.
- Cadence lock. Sometimes the sensor latches onto your step rhythm instead of your pulse. If your “heart rate” sits at 160–175 and matches your steps per minute almost exactly, that’s a clue.
- Cold skin, tattoos, and wrist movement can all make it worse.
What to do: if the number looks wrong, try a Bluetooth chest strap for a few runs and compare. iRunning connects to standard Bluetooth heart-rate straps, free.
6. The route and the treadmill
Small hills you barely notice raise your heart rate. So does running into the wind. On a treadmill, the lack of moving air makes you hotter, and belts vary, so the same speed can feel harder than outside. (More in our treadmill guide.)
What to do: compare runs on the same flat route, and point a fan at yourself indoors.
When to get it checked
Most high readings on easy runs have a boring explanation. Stop and see a doctor if a high heart rate comes with chest pain or pressure, dizziness, fainting, unusual shortness of breath, or a racing or irregular heartbeat that doesn’t settle when you stop. The same goes if you have a heart condition or take medication that affects your heart rate.
What actually works
- Slow down more than feels reasonable, and use walk breaks without guilt.
- Check your zones against the talk test, and fix your max if they don’t match.
- Compare like with like: similar weather, same route, same time of day.
- Give it time. Most people see their easy pace get faster at the same heart rate over roughly two months of regular easy running. That’s the whole point of zone 2 training.
How iRunning helps you stay easy
- You see your zone while you run. Heart rate and your current zone, from an Apple Watch or a Bluetooth strap. More on the zones in Heart Rate Zones Explained.
- A voice tells you when you drift. Build a workout with a zone 2 target, and you hear “Heart rate too high” when you go over and “Heart rate too low” when you drop under. The same warning repeats at most every 20 seconds, so it nudges rather than nags. The watch shows an alert too.
- After the run you see time in each zone, so you know whether “easy” really was easy.
Heart-rate zones, alerts, strap support and two custom workouts are free. So is the Easy run preset: 30 minutes, conversational. If you want the whole eight weeks laid out, the Zone 2 Base Builder plan (Premium) starts and ends with the same 5K at the same heart rate, so you can see the change as a number. New to running? The free From Walk to Run plan is a gentler start (more about walk-to-5K plans).
Training advice, not medical advice. Check with a doctor before starting if you have a health condition or have been inactive for a while.