80/20 Running: Why Most
Runners Train Too Hard

The counterintuitive truth about training intensity

Most recreational runners believe that harder training produces better results. It feels logical: if running fast is the goal, training fast should help you get there. The reality, supported by a substantial body of endurance research, is more nuanced — and it suggests that most runners would improve faster by running slower more of the time.

This is the core of the 80/20 principle, also called polarised training: broadly, a high proportion of training at low intensity, with a smaller amount at high intensity and relatively little threshold work; exact distributions vary by athlete and study.

The research behind polarised training

The most comprehensive direct comparison of training models comes from a 2014 study by Thomas Stoggl and Billy Sperlich, published in Frontiers in Physiology. The researchers assigned 48 well-trained endurance athletes to four different training models: high volume, high intensity, threshold (tempo), and polarised (80/20). In this nine-week trial, the polarised group showed the greatest improvements in VO2peak, time to exhaustion and peak velocity/power; work economy did not differ significantly between groups.

The finding is counterintuitive but robust: not the runners who trained hardest improved the most. The runners who protected their easy runs made them genuinely easy — and then went very hard on their hard days — showed the best adaptations.

What "genuinely easy" actually means

Here is the problem: most runners do not run easy enough on their easy days. When asked to run at easy effort, many default to a moderate effort — not slow enough to be restorative and stimulate the aerobic base adaptations that easy running produces, but not hard enough to create the high-intensity adaptations that are the goal of harder sessions. This is the grey zone, and it is where training progress stalls.

Genuinely easy running means:

• You can hold a full conversation in complete sentences without pausing to breathe.
• Heart-rate zones depend on the method used and individual physiology — use conversational effort or a personalised heart-rate framework rather than treating 60–70% of maximum as a universal definition.
• You finish the run feeling like you could have run for significantly longer.
• The pace feels almost embarrassingly slow compared to what you could do.

For many runners, this is 60–90 seconds per mile slower than their average run pace. It feels wrong. It feels like you are not doing enough. You are doing exactly enough.

Why cadence helps you stay in the easy zone

One of the most common ways runners drift into the grey zone is by unconsciously increasing pace as a run progresses and the body warms up. The effort feels the same — but the pace has crept up.

Running with a cadence target provides a secondary anchor. If you are running at a cadence consistent with your easy-pace target, you have a built-in mechanism for noticing when things are drifting. Cadence can change with pace, terrain and fatigue — treat it as an additional reference, not a direct intensity measure.

More broadly, cadence awareness helps you develop a better internal model of your effort zones — something that improves over time but starts with learning to notice what running at different intensities actually feels like in your body.