Polarized 80/20 training, explained
Why most runners run their easy days too hard, and the simple 80/20 fix backed by research.
Run 20 to 40 km a week and not getting faster? The cause is usually the same. You run your easy days too hard.
This is the core idea of polarized training. It comes from Stephen Seiler’s research on top endurance athletes. Polarized just means you split your week into two buckets: very easy and very hard. Not much in between. It is also built into Kinoku’s Zone Training feature. Here is the short version.
The five-zone model
You can sort run intensity into five zones. Each one is set by your heart rate or your pace.
| Zone | How hard | What it feels like |
|---|---|---|
| 1, Recovery | Very easy | Could chat all day |
| 2, Easy | Easy | Full sentences, nose breathing is fine |
| 3, Tempo | Medium-hard | Short sentences, breath picks up |
| 4, Threshold | Hard | One word at a time |
| 5, Interval | Very hard | Can’t talk |
Most coached runners spend their week in Zone 2 (easy long runs) and Zone 4 to 5 (interval days). Almost nothing in Zone 3.
Why Zone 3 is a trap
Zone 3 is the tempo zone. Medium-hard, and you can hold it for 20 to 60 minutes. It feels useful. You move, you sweat, you finish tired. But it is the worst zone to live in. Here is why.
- It is too hard to bounce back from fast. So you can’t follow a Zone 3 day with another hard day.
- It is too easy to drive real change. Your body misses the hard push that builds fitness. It also misses the slow, high-volume work that builds the small parts of your muscles that turn fuel into energy.
Spend most of your week in Zone 3 and you get a runner who is always tired and never improving.
The 80/20 fix
Spend about 80% of your run time in Zone 1 to 2. That is the very easy, can-talk pace. Spend about 20% in Zone 4 to 5. That is hard intervals or threshold work. Spend almost no time in Zone 3.
This feels backward. Run easier more often? But it is how the best endurance athletes in the world train. The slow runs have to stay slow. That is what makes the fast runs fast.
How Kinoku scores it
Every GPS run you log is sorted into zones by your pace. Then Kinoku adds up your weekly polarized score. It is the share of your time spent easy versus hard. If you are stuck in the tempo zone, you will see it on the dashboard within two weeks.
Kinoku also gives each run a Training Effect score from 0.0 to 5.0. The number shows how much that run pushed your body. A 90-minute easy base run might score 2.5. A session of 6 × 800m intervals might score 4.0. Both runs help. They just work different systems, and the mix is what builds fitness.
The takeaway
Run easier on easy days. Run harder on hard days. Stay out of the middle. Do that for 8 to 12 weeks and you will get faster, even if your weekly distance stays the same. It is the cheapest speed gain in running.
Zone Training is part of Kinoku Pro. You’ll find it on the Run Analytics dashboard.