80/20 training: What it is, and how it works

The 80/20 triathlon training method, which leaves you less fatigued and performing better, is gaining popularity. Discover how to reach your performance peak with this train slow, race fast formula

Credit:The Secret Studio

What is 80/20 training?

With 80/20 training you spend 80% of your time working out at a low intensity and 20% at a high intensity. 


The majority of age-group triathletes can benefit from cranking down their intensity,” Dr Stephen Seiler of the University of Agder in Norway tells us. “Too many recreational triathletes fall into the moderate-intensity trap and neither maximise stamina or speed adaptations.” 

Yes, it’s true – research undertaken by Seiler into the training programmes of elite endurance athletes, including triathletes, shows that around 80% of their weekly training is nestled under the ventilatory threshold (see overleaf). Only 20% is over. 

Seiler has also shown that the 80/20 split works whether you’re training four or 24 hours a week, whatever your tri distance, and, like the elites, the easy (80%) sessions should be done under threshold, while the harder 20 component is threshold and over. 

Seiler wrote the foreword in 80/20 Triathlon, co-written by Matt Fitzgerald and David Warden, the latter who now takes over to provide your complete guide to the 80/20 training method…  


Avoid scheduling workouts of the same type close together. For example, while there’s nothing wrong with cycling and running on the same day, just avoid high-intensity in both. If you’re in the majority and can’t train four times a week in each discipline, that’s fine. All that matters is that whatever mix you include in a given week, it hits the 80/20 split. And remember: moderate- and high-intensity efforts aren’t performed exclusively at this level and include recovery work at lower intensity, which you can add to the 80 part.

Within each discipline there are four basic categories of workout: 

a) Easy swims, rides and runs – relatively short sessions in zone 1 and/or 2 (zone descriptions to follow); 

b) Long endurance-boosting workouts (zone 1 and 2); 

c) Moderate-intensity sessions (zone 3 or X); 

d) High-intensity workouts (zones 4 and 5). 


Six times a week is a sweet spot for many triathletes. It allows for a day off and just one session a day for the remainder of the week. An ideal schedule would look like this:

 A complete day off on Monday.

A run that includes high-intensity intervals on Tuesday.

Swimming long on Wednesday or a short swim that includes high-intensity intervals.

Cycling on Thursday with high-intensity intervals.

Swimming again on Friday with high-intensity intervals.

A long endurance run on Saturday that could optionally include some high-intensity efforts.

A long endurance cycling session on Sunday that could include some high-intensity efforts.


There are many methods to measure intensity, though none are perfect. Seiler recommends a “triangulation of methods”, using a combination of heart rate, perceived exertion and pacing. When it comes to heart rate monitors, we’d go for a chest strap version for greater accuracy. They’re good for holding pace during low-intensity sessions but slightly inaccurate during high-intensity efforts due to your heart taking up to 30secs to catch up to a hard effort. Also, they’re not appropriate for the swim. 

Perceived exertion (RPE) is how your brain perceives you feel. Hence, it’s arguably the most accurate indicator. Use a simple 1 to 10 system where one is extremely easy and 10 is extremely hard. On the downside, it’s hard to monitor this rating when really fatigued.

Pacing via GPS is great for monitoring and controlling efforts in moderate- and high-intensity runs but can feel restrictive at low-intensity efforts. Power meters also come into the equation and are, of course, extremely accurate on the bike. 

What is ventilatory threshold (VT) and why is it important?

“It lies between 77 and 79% and is the breathing point where lactate begins to accumulate in the blood and, broadly speaking, is similar to the lactate threshold,” says Seiler. “Studies show that you don’t develop as strongly as those following the 80/20, or polarised, model.” Physiologically why isn’t 100% proven but one of the key players seems to be a cell-signalling compound called interleukin-6 (IL-6). High levels of glycogen depletion, as per long, slow efforts, triggers high levels of IL-6. Consistent low-intensity training stimulates physical adaptations that reduce IL-6 during future triathlon sessions and, in turn, elevates endurance. You’re then more fatigue resistant to build speed during the 20% element.


There’s no evidence that suggests a change in intensity balance for an individual discipline based on a strength or weakness. Certainly, the aggregate of all three disciplines should still result in a ratio of 80/20, but the duration should increase for your weakest discipline. That said, if, for example, you were to increase total running time because running is a weakness, you might need to shift the intensity balance to 85/15 for running to avoid burnout and compensate with a bit more intensity on the swim and bike.


As your fitness grows and your zones are adjusted, your training load, which includes both volume and intensity, should gradually increase. For instance, your training load in week 16 shouldn’t be the same as week five. But the load shouldn’t continually rise or, coupled with everything else in your life, you risk burnout. So every third or fourth week, pencil in a recovery week where you reduce training load. Cut total training hours by 30-40% compared to the previous week: 30% is fine during lighter periods (like around now); 40% during heavier periods, such as the build-up period to your race. Which brings us on to periodisation…


Focus on increasing your swim, bike and run thresholds for the first eight weeks with the bulk of your interval training
(20) near threshold pace. Eight to nine weeks before your race, shift your moderate- and high-intensity training
to match the duration and intensity expected on race day. Keep the ratios in both periods at 80/20. If that sounds like regular ‘General’ and ‘Specific’ phases from traditional periodisation, that’s because it is. Why? Because 80/20 fits
into any training methodology. Classic periodisation, reverse periodisation, block periodisation… regardless of the periodisation system, the best results come from spending 80% of your time
at low intensity and 20% of your time at moderate to high intensity.


Unlike with the bike and run, heart rate monitoring is too erratic to set swim zones. That’s where swim pacing comes in. You see, with a simple test you can find your lactate threshold swim pace (LTSP), which you can then use to set your swim zones. To do this, you need to perform a critical velocity (CV, which is metres per minute) test. 

Simply swim 400m as hard as you can. Rest for 2mins and then swim 200m as fast as you can. You can then follow quite a complex formula to find relevant zones with 100% of CV equivalent of your LTSP. [We would follow Warden’s advice and take these 400m and 200m times to the online calculator at 8020endurance.com/8020-zone-calculator/. For reference, we’ve included a table of zones (below) based on these calculations, including both speed (CV) and pace, but using the pacing information. Why? Because CV isn’t practical to use in a pool. For instance, can you track zone 2 if we asked you to swim @ 56m per minute?!]


Swim drills are vital to improve your front crawl and play an integral role in your 80% part as they should be performed at low intensity. Drills are broadly broken down into those that reduce drag or those that increase propulsion efficiency. An example of reducing drag is the catch-up drill where you keep your left arm extended in front of your body until the opposite hand has entered the water. Begin the pulling action while the right arm waits for the left to ‘catch up’. 

A propulsion drill is where you swim with an exaggerated high elbow, bending your arm to 90° at the beginning of the pull and keeping the elbow as close to the surface as possible while your hand and forearm sweep backwards like a paddle.


Your lactate threshold heart rate  (LTHR) roughly corresponds to ventilatory threshold. To find yours, do this 30min
TT. Find a relatively flat course and warm up for 10mins. You should be perspiring lightly. Then raise the intensity to the level you think you can hold for 30mins. Press the lap button on your heart rate monitor. Hit lap again after 10mins. TT for 20mins more and press again. You have 10min and 20min laps. Your LTHR is the average heart rate (in bpm) for the final 20mins.


The clear distinction between hard and easy sessions gives you the ideal platform to focus on cadence. Research shows that optimum cadence is about 90rpm, striking the perfect point between power output and fatigue resistance, in addition to preserving glycogen stores, which is key the longer you race. However, unless you’re from a cycling background, new triathletes often fall between 80-85rpm, mimicking the moderate-intensity training black spot we want to avoid. For each bike session, aim to hit 90rpm, selecting the appropriate gear depending on whether it’s an easy or hard session


Determining your LTHR for your run requires following the same protocol as the bike – albeit, of course, without the bike. So read the previous page and follow the 10min/20min TTs. Don’t take a shortcut and feel you can simply transfer your bike LTHR and respective zones to running. Your run LTHR is usually a few beats higher than cycling. That said, if you much prefer gauging runs by speed (and via your GPS), you can calculate your threshold pace (TP). Warm up for 10mins, run as far as you can for 30mins. Your TP is your average pace over the 30mins. So if you covered four miles in 30mins, your TP is 8mph.


It’s not as technique heavy as swimming but running efficiently still demands excellent skill. Simply running forges a technique suitable for you but you can improve it with brief run drills during your low-intensity sessions. One example is to run with your hands on your head. You can’t project forward without bouncing up and down, but too much vertical oscillation leaches energy. By running with your hands on your head, you’ll be more aware of the bouncing and can alter your run form to reduce the bobbing. 


Focus less on the quantity of food and more on the quality of your food choices. High-quality foods are natural, unprocessed food types that humans have been eating for centuries. In the 80/20 classification system, there are six food types: vegetables; fruit; nuts, seeds and healthy oils; whole grains; dairy; and unprocessed meat and seafood. Tick these off every day. Look to avoid refined grains, sweets, processed meat and fried foods. Another quantity pointer: reduce carb intake on rest days.


Shorter sessions, whether they’re swim, bike or run, or high or low intensity, don’t require any extra fuelling. Your glycogen levels are sufficient to fuel your working muscles. That said, sip on a bottle, whether it’s water or electrolytes.
When it comes to sessions over an hour, traditional fuelling advice applies, namely 60-90g of carbohydrates per hour. You could top up longer sessions with a protein gel to begin muscle repair. 


What you eat after training depends on intensity. If it’s a harder session, you should consume a healthy, carbohydrate- and protein-rich snack within an hour after finishing. This could be a commercial protein/carb shake. Follow this with a healthy meal within two hours. If it’s an easier session, the choice is yours. You could follow this template or you could drop the shake and opt for a healthy meal.



A proven idea to rank up fat metabolism and spare precious glycogen stores is to undertake a fasted run or ride. On the 80/20 programme, trying this once every three weeks is fine. It’s usually easier to have a fasted training session first thing in the morning – before breakfast – and simply maintain your energy levels by refuelling on water. Keep the intensity low with the duration up to you, but
one to two hours for biking is optimum. Take an energy bar with you in case you feel faint