Why most of your running should feel easy: the 80/20 rule
By Coach Kura4 min read
Most runners who stop improving are not lazy. They run their easy days a little too hard and their hard days not quite hard enough. The 80/20 rule is the simplest fix, and it sits at the centre of Coach Kura’s method.
What the 80/20 rule says
Spend about 80% of your weekly training time in easy zones and about 20% in hard zones. Count time, not the number of runs. A runner training five hours a week would spend about four hours easy and about one hour in hard work across the week.
This split is one of the best-supported findings in endurance sport research. It is not a compromise between easy and hard. For most runners it is simply what works.
Why easy running builds your aerobic efficiency
Easy running is where your body builds the parts that make running cheap: more mitochondria in the muscles, more capillaries to carry oxygen, and a heart that pumps more blood with each beat. These grow because easy volume is high and its cost is low, so you can do a lot of it and still recover.
Hard running lifts your ceiling: your threshold and your top aerobic power. A little goes a long way. More than you can absorb just digs a fatigue hole.
Picture two runners at the same pace. One is at 185 beats per minute, the other at 155. Their ceiling may be the same, but the second runner is far fitter, because the same pace costs them much less. That is aerobic efficiency. Easy running is how it grows, and over months it helps your TAEI (AKURA Endurance Index) rise: the number AKURA works out from your best recent race efforts to set your training paces.
The grey-zone trap
The most common mistake is running every day at medium-hard. It is too hard to build the base cheaply, too easy to lift the ceiling, and tiring enough to spoil the sessions that should be hard. Group runs often end up here, because the pace is set by the fastest person in the group.
The six AISRI zones
Coach Kura’s method uses six heart-rate zones. The first three are easy; the last three are hard.
| Zone | Feels like | % of max HR | Mainly builds |
|---|---|---|---|
| AR · Active recovery | Very easy | 60–68% | Recovery |
| F · Foundation | Easy, you can talk in full sentences | 68–78% | Mitochondria, capillaries |
| EN · Endurance | Steady, still controlled | 76–85% | Aerobic durability |
| TH · Threshold | Comfortably hard | 88–92% | Lactate threshold |
| P · Power | Hard intervals | 92–97% | Top aerobic power |
| SP · Speed | Short and fast | 97–100% | Speed and running economy |
Finding your easy heart rate
A common estimate of maximum heart rate is 208 minus 0.7 times your age. For a 40-year-old that is 208 − 28 = 180 beats per minute. It is only an estimate: a real maximum seen on your watch in a hard race is better.
With a maximum of 180, the Foundation zone (68–78%) is about 122 to 140 beats per minute. If that feels too slow, that is normal at first. Use the talk test as a check: on an easy run you can speak in full sentences.
Easy running in Chennai heat
Heat and humidity push your heart rate up at the same pace. On a hot, humid morning your easy pace will be slower than on a cool one, and that is fine. Let heart rate and effort set your easy days, not the pace you ran last month.
- Run early, before the sun is high.
- Carry water on longer runs.
- Keep hard sessions for cooler mornings when you can.
How AKURA puts this into practice
Every session in your AKURA plan is tagged with a zone, and your coach sets the mix of easy and hard for the week. Your morning readiness check then decides how hard today should be: when readiness is low, only the easy zones stay open, and a hard session is eased back to an easy run.
Please note: This article is general training information, not medical advice. If you have pain, an injury, a heart condition or feel unwell in the heat, stop and speak to a doctor before you train.