The 75% rule says at least 75% of your weekly riding time should stay below roughly 75% of your maximum heart rate — easy endurance work — with the remaining 25% for tempo, threshold, and interval riding.
What the 75% rule says
The 75% rule — popularized in cycling training literature such as Joe Friel's Cyclist's Training Bible — is a simple intensity distribution guideline: at least 75% of weekly riding time happens below about 75% of maximum heart rate, and no more than 25% of time goes to harder work.
It exists to solve the most common amateur mistake: riding everything at a medium-hard effort. That pace is too hard to build a base and too easy to raise your ceiling — the dead zone where riders plateau for years.
75% vs polarized 80/20 vs pyramidal
| Model | Easy / hard split | Shape | Best for |
|---|---|---|---|
| 75% rule | ~75% easy / 25% moderate-hard | Time below ~75% of max HR | Simple guideline for time-crunched riders |
| Polarized 80/20 | ~80% very easy / 20% very hard | Almost no moderate work | Racers and high-volume athletes |
| Pyramidal | Z2 > Z3 > Z4 | Tapered pyramid, some threshold | Endurance event preparation |
How to apply it
- Estimate your max HR — 220 minus age is a rough starting point; a field test or LTHR-based zones are better.
- Calculate 75% of that number: for a 40-year-old with a max HR of 180, that means most riding below about 135 bpm.
- Count time, not miles: 8 hours per week means at least 6 hours genuinely below the line.
- Concentrate the hard 25% into 2–3 focused sessions rather than letting it leak into every ride.
- Recheck with a real heart rate strap — perceived easy is often 10 bpm too high.
Why easy riding makes you faster
Time below the line is what builds the aerobic engine: more capillaries, more mitochondria, better fat metabolism, a bigger stroke volume. Those adaptations need long, easy exposure — they do not respond to moderate surges.
The paradox riders resist: slowing down the easy days is what lets the hard days get faster. Collect both and your sustainable power climbs without adding hours.
See it in practice
Generate an endurance session below to see exactly what a below-the-line ride looks like — zone targets, duration, and cadence guidance for a proper easy day.
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