Successful endurance athletes do most of their training at low intensity and only a small share hard. This pattern is often summarised as "80/20": about 80% easy and 20% moderate-to-hard.
Evidence
- Elite athletes: Seiler & Kjerland studied elite endurance athletes and found about 75% of sessions were below the first ventilatory threshold. Most of the rest were high intensity, with little in between. Seiler's 2010 review reached the same conclusion across sports.
- Recreational runners: Esteve-Lanao et al. (2007) randomised runners to about 80% vs 65% low-intensity training over 5 months with equal total load. The 80% group improved more over a 10.4 km course.
- Trained athletes: Stöggl & Sperlich (2014) found a polarised programme improved VO2max and time to exhaustion more than threshold-, high-intensity- or high-volume-focused training over 9 weeks.
Common mistake
Recreational runners tend to run their easy days too fast, in a moderate "grey zone" that is too hard to recover from and too easy to drive adaptation. Fitzgerald (80/20 Running) argues this is the most common error in amateur training. Slowing easy runs down is usually the first improvement to make.
If your dashboard warns that only a small share of your recent runs were easy, your plan should:
- explain why easy days must be truly easy;
- keep quality sessions limited and purposeful;
- prefer adding easy distance over adding intensity.
How Trainer applies it
- At least 75% of each week's training distance must be easy (races excluded). Plans should aim for about 80%.
- Easy runs are at E pace. If you have heart rate data, they stay under 79% of your max heart rate, the top of Daniels' E range. The dashboard shows this ceiling.
- The dashboard counts a recent run as easy if its average heart rate was under that ceiling, or, without heart rate data, if it was slower than M pace. It warns you when under 60% of your runs in the last 12 weeks were easy.
Sources
- Seiler KS, Kjerland GØ. Quantifying training intensity distribution in elite endurance athletes: is there evidence for an "optimal" distribution? Scand J Med Sci Sports. 2006;16(1):49–56.
- Seiler S. What is best practice for training intensity and duration distribution in endurance athletes? Int J Sports Physiol Perform. 2010;5(3):276–291.
- Esteve-Lanao J, et al. Impact of training intensity distribution on performance in endurance athletes. J Strength Cond Res. 2007;21(3):943–949.
- Stöggl T, Sperlich B. Polarized training has greater impact on key endurance variables than threshold, high intensity, or high volume training. Front Physiol. 2014;5:33.
- Fitzgerald M. 80/20 Running. New American Library; 2014.