Polar lied to me
I’ve been back to running for less than a month now — two sessions a week — and I still have a decent endurance base from hiking, including a mini-trek of 54 km over two days. Nothing exceptional, but enough to think I could handle some light training. Except…
Since getting back into running, I’ve felt like a complete noob. Everywhere you read that to run in aerobic (zone 2) training, you need to stay in zone 2. Except…
As soon as I start jogging, I’m in zone 3. If I speed up just a little, I’m in zone 4, the threshold zone. I remember one session where I tried to stay in zone 2 and ended up running at 9:30 min/km — barely over 6 km/h. I walk faster than that when hiking. Sure, I was tired that day, but still…
Basically, since I restarted, I’ve never done a run in zone 2 — always in zone 3, sometimes flirting with zone 4.
Back to the Basics
I’m 44 years old, with a theoretical max heart rate (HRmax) of 176 bpm and a resting heart rate of 56 bpm.
Polar automatically splits my zones like this:
| Start | End | |
|---|---|---|
| Z1 | 88 | 105 |
| Z2 | 106 | 122 |
| Z3 | 123 | 140 |
| Z4 | 141 | 157 |
| Z5 | 158 | 176 |
And yet, every run I’m around 145 bpm — which puts me right in zone 4. Not great…
The Breaking Point
One day I’d had enough — like I mentioned in my last running post. Fed up with the track, the watch, all of it. So I went out and just ran by feel, pushing myself to break 30 minutes on a 5 km. I didn’t care about zones, pace, or beeps from the watch. I just wanted to enjoy it — and pushing hard actually felt good.
Back home, I synced the watch and looked at the data more closely. Turns out, my heart rate peaked not at 176 bpm, but at 190 bpm.
At first, I was kind of proud — I’d just smashed the “theoretical” HRmax. Heart of a champion, right? So I updated my HRmax in Polar, which changed my zones to:
| Start | End | |
|---|---|---|
| Z1 | 95 | 113 |
| Z2 | 114 | 132 |
| Z3 | 133 | 151 |
| Z4 | 152 | 170 |
| Z5 | 171 | 190 |
That already made a lot more sense. I can now run without being out of breath — I can talk, meaning I am in aerobic endurance — even if the watch still says zone 3. At least I’m no longer in zone 4 at 145 bpm.
The Karvonen Formula
While digging around, I came across the Karvonen formula, which doesn’t just use HRmax, but the heart rate reserve — the difference between your resting and max heart rate.
For me, that’s 190 – 56 = 134 bpm. Using this, my zones look like this:
| Start | End | |
|---|---|---|
| Z1 | 123 | 136 |
| Z2 | 137 | 150 |
| Z3 | 151 | 164 |
| Z4 | 165 | 177 |
| Z5 | 178 | 190 |
And suddenly, everything clicked. When I run “easy” — around 145 bpm — I’m actually in zone 2, not flirting with the threshold zone.
That changes everything.
The Takeaway
Since then, my runs feel completely different. I run relaxed, at ease, without stressing about every beep from my watch. And most importantly, I finally know that I wasn’t out of shape — my watch just didn’t know me yet.