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80: 20 Training – What is it, why and how should we do it?

80: 20 training is a concept that’s really popular right now but what is it, what does it do, how should endurance athletes do it and what are the pro’s and con’s??

What is it?

80: 20 training is when most (the 80 bit) training is done at an easy pace and the other 20 is done much faster. It’s also called ‘polarised’ training.

80: 20 training is useful for endurance athletes whose events are predominantly aerobic and who are fully physically developed ie. past puberty.

It was made popular by a famous exercise scientist, Stephen Seiler, who found that most elite endurance athletes across a range of sports such as running, triathlon, cycling and cross country skiing did most of their training either at a very slow or a fast pace. A key finding was they didn’t train much at intensities between fast and slow. One thing that Seiler found out about beginner and moderately developed athletes was that they trained in the middle ‘junk miles’ zone most of the time (sounds like most club sessions?) and he now says that people should do lower intensity training on their own or with others working at the same pace to avoid working too hard.

Why do it?

In 80: 20 training, athletes spend most of their training time in a low intensity zone and this develops the aerobic system by many mechanisms eg. increasing plasma volume, red blood cells, mitochondrial density in the muscles, heart chamber size and stroke volume. These CENTRAL changes allow a greater stroke volume which means more blood is pumped for each heartbeat which takes more oxygen to the working muscles. In the remaining 20%, training is more intense and causes PERIPHERAL changes at the blood-muscle boundary and within muscles themselves. This more intense training develops important qualities like Vo2and vVO2. Think of the 80% being layers of undercoat and the 20% being the gloss on top.

The argument for 80: 20 is that by developing central adaptations this allows the peripheral ones to work best.

How should it be done?

The slow 80% needs to be fast enough to stress the body but slow enough to be easy. This can be measured in all sorts of ways using effort ratings, blood lactate testing or heart rate. The key point is that the pace should be just above the first ventilatory threshold which is the speed when breathing and heart rate first kick up.

It’s also the point where lactate levels start to kick up:

What goes into the mix in the fast 20%? Well that depends – on your fitness, your goals, target event and the time you have. What a Park Run newbie needs for a 5Km PB is different to for an experienced triathlete aiming for 70.2. One size does not fit all.


80: 20 works well for many, it helps prevent burn out by doing too much hard training, improves central adaptations and is effective for cardiovascular health and general endurance. It allows for social running and can be initially useful in building robust athletes.

There is also evidence that lower intensity training can help with recovery between sessions and allows better performance in the harder sessions.


A key issue is how slow is slow? Many athletes do not know how to hit the sweet spot of ‘just above the first ventilatory threshold’. And it is individual – everybody is different, so pack runs are often the wrong pace ending up in junk miles, caught between too fast for the 80 and too slow for the 20.

Too slow and you won’t be stressing the body sufficiently to cause adaptation – getting fitter.

Slow is defined as less than 70% of maximum heart rate. So, the question is ‘how do you calculate your max heart rate?’ The old way of 220 minus your age is now discounted as it can be wrong by up to 20 beats per minute.

Many athletes rely on heart rate zones but how are these calculated, do they fit you and are they accurate? Seiler identified 3 and scientific testing can show many zones by analysing the gas composition of exhaled breaths in testing, but most commercial devices use heart rate and apply their own formula to everyone assuming the average fits all. In most people, the zones are grey areas that merge into each other and there may not be a specific heart rate where one zone ends, and another starts. It is also affected by lots of factors like altitude, temperature, wind if your outside, fatigue etc.

Variations of 80: 20 are used for marketing, to get people to buy ideas which are not scientifically accurate or validated. It might be a famous brand of watch that plans training and which training zone you have spent so much time in but can be up to 30% inaccurate. Or a type of training eg. Lydiard but you’ll need to buy onto a course to learn about it. Or it might be a philosophy of training like MAF which uses its own concept called ADS (aerobic deficiency syndrome) which lacks scienctific support, but it’s explained if you buy a coaching programme from the website.

A key issue is what goes in the 20? The 80 might provide the foundations but it’s the 20 that gets the PBs. Beginner athletes will probably benefit from a range of faster running but the more specific the fitness gains are, the more targeted the mix needs to be. We all want to run faster but what should we target and when? VO2, vVO2, lactate threshold, lactate buffering? They all need different types of sessions.

There is also the issue of doing most running slowly using the same gait, this can cause overload injuries.

Ask your Coach what is needed for each? He or she probably does not know if in the UK, as it’s not in current coaching qualifications. If they don’t, ask someone who does…

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