80/20 Triathlon Training: The What, Why, and How

The general premise behind the 80/20 rule for triathlon and endurance training: spend a lot of time training relatively easy, and then spend some time training hard – guides a vast majority of endurance training plans. But why? And how does an 80/20 training plan work, exactly? Let’s dive into it: the what, why, and how of the 80/20 training strategy. What it is, why it’s so effective, and how you implement it in practice.

Scroll far below for our 16-week 80/20 triathlon training plan for the 70.3 distance.

What is the 80/20 endurance training strategy?

Dr. Stephen Seiler, Professor of Sports Science at Norway’s University of Agder, was the first to coin the term “80/20 training.” This isn’t to say that he invented the concept – elite-level endurance athletes had been using this general approach for their training long before he defined it. Seiler was the first, though, to formally recognize the widespread usage and success of the general strategy, put specific parameters around the time spent training in low- and high-intensity zones, and promote the approach for endurance athletes.

Seiler’s 80/20 rule is relatively straightforward: It dictates that an athlete spends 80% of their weekly training time at low intensity and the remaining 20% at high intensity. The devil, however, is in the details. Seiler’s work at the University of Agder was rooted in science, and so the seemingly vague direction to divide your time between low- and high-intensity training actually requires a very specific understanding of what low- and high-intensity means.

Seiler defines low-intensity training as training done below your aerobic threshold. That’s your aerobic threshold, not to be confused with the more commonly-known anaerobic threshold. Which now, of course, begs the question: What is aerobic threshold? Your aerobic threshold is the dividing line between when you are entirely reliant on your aerobic (oxygen-based) energy systems to fuel your muscles and when you just barely begin to utilize your anaerobic energy system to help your aerobic energy system produce fuel. Your aerobic threshold is also, conveniently, the upper limit of Zone 2 in a typical 5-zone heart-rate training system.

High-intensity training is done – logically – above your aerobic threshold. Seiler emphasizes work done at or above your anaerobic, or lactate, threshold in his 80/20 training strategy, advising that much of the high-intensity work should be in Zones 4 and 5 with little emphasis placed on Zone 3. For this reason, his 80/20 strategy is often referred to as polarized training. A broader interpretation of Seiler’s 80/20 rule has been adopted as the approach has gained in popularity, with high-intensity work spanning Zones 3 through 5.

Whether you prefer a true polarized training strategy or a more generalized 80/20 approach, one thing is certain: You must know and adhere to your training zones in order to properly execute and reap the benefits of an 80/20 training plan. If you’re a bit off in your low-intensity execution and your effort level slides just above your aerobic threshold, your 80/20 plan just became 65/35 or even 50/50, and you’ve lost the whole point of the strategy.

Why is the 80/20 endurance training strategy so effective?

So, what is the point of the 80/20 strategy? Why has the 80/20 rule gained such popularity, and why are people seeing success with this approach? The effectiveness lies largely in that 80%. Spending huge amounts of time training below your aerobic threshold – in your aerobic training zones, a.k.a. Zones 1 and 2 – builds a huge aerobic engine.

But how does training below your aerobic threshold do that? Your aerobic energy system is bound by the amount of oxygen it receives from your cardiovascular system; your VO2 Max defines that upper limit. Training in your aerobic zones increases cardiovascular capacity and efficiency, which increases your VO2 Max. That improvement results in increased delivery of oxygen to your muscles at lower corresponding heart rates. This means you can go faster for longer and that, as it should go without stating, is the entire point of training.

(For a more detailed discussion of VO2 Max, see: How to Improve Your VO2 Max)

Of course that 20% at high-intensity serves a purpose too. High-intensity work plays its own part in improving VO2 Max as well as specifically preparing you for the first and fast 100m of the swim, hills and passes on the bike, hills on the run, and your race effort in general. But the secret sauce on the high-intensity side is in its limited nature.

Our body responds to stress – both physical and psychological – by calling on our stress response system. So during intense exercise sessions, our bodies initiate that stress response and activate the sympathetic-adrenomedullary (SAM) and hypothalamus-pituitary-adrenal (HPA) axes. The SAM and HPA axes respond to stress by – among other things – increasing heart rate, cardiac output, and blood glucose levels and releasing adrenaline and cortisol. While that sounds great to support an isolated high-intensity training session or a race, constant activation of the stress response system has negative consequences. The 80/20 rule, therefore, establishes a training protocol where most sessions fly under the stress radar and do not trigger the stress response system.

And the effectiveness of the 80/20 training approach is more than just a theory – it’s been proven in numerous studies of endurance athletes’ training and race results. One study carried out by Seiler and his colleagues, for example, compared athletes who trained adhering to the 80/20 rule with those using a 50/50 split between low-intensity and high-intensity training. While both groups improved their 10k times, the 80/20 group’s average improvement was nearly 40% higher than the 50/50 group.

How to implement 80/20 endurance training strategy in triathlon training

Assuming you’re now on board with implementing the 80/20 rule within your training, you’re probably wondering how to actually do that. It turns out, it requires some work, some diligence, and some planning.

First, you’ll need to identify your pace, power, and/or heart rate zones for swim, bike, and run. You can do this on your own using field tests – tests that you can conduct yourself, essentially time trials for each discipline – or if you want to be super fancy you can find a lab that does threshold testing for bike and/or run training zones. You want to define zones for at least one metric for each sport and commit those pace, power, and/or heart rate numbers to memory. Cheat sheets might be helpful here – that’s a lot of numbers. We won’t go into zone setting here, but Triathlete has great resources to help you establish your zones—whether you use heart rate, power, or pace.

Second, you need to make sure that you can track and adhere to those zones in training. You’ll need a multisport watch, and maybe a bike computer, properly configured so that you can pay close attention to your bike and run data – and then you have to actually pay close attention to your data throughout each training session. (Fair warning: If you’re used to zoning out and enjoying the scenery, this will take some getting used to.) You’ll also need to dial in your rate of perceived exertion (RPE) on the swim so that you are hitting your zones without the benefit of constant data.

Finally, you’ll need to do some planning and some (maybe a lot) of math. Ensuring that you’re right around that 20% mark for high-intensity training each week cannot be accomplished by just winging it. Getting there by executing 20% of your workouts at high intensity doesn’t work, because that’s very different from executing 20% of your training minutes at high intensity. So each week you’ll need to plan out your training: total minutes, minutes in Zones 1 and 2, and minutes in Zones 3 through 5. Do the math, see if you’re right around that 80/20 split, adjust if not, repeat math, repeat 80/20 check until you get it right.

If that sounds like a lot of planning and a lot of math, you’re not wrong. Finding an 80/20 training plan for your race distance, where someone else has done all the math for you, is way easier. So lucky for you, we’ve got one option right here.

80/20 triathlon training plan for 70.3

Distance overview

This 16-week 80/20 training plan is designed for triathletes racing the 70.3-distance who have at least one season of experience racing long-course triathlon. Each week has been carefully designed so that 80% of the training (give or take a few percent, and excluding race week) will be executed in Zones 1 and 2, and the remainder in Zones 3+.

A typical week has three swims, three bikes, three runs, and two recommended strength sessions. Your long rides are on Saturdays and your long runs are on Sundays. Mondays are your off days; optionally, you can move up the scheduled Sunday aerobic swim by six days to Monday. There are brick workouts on Saturdays beginning with week 5.

The plan begins with 4800 yards/meters of swimming, 3 hours 15 minutes of cycling, and 2 hours 20 minutes of running total in the first week. It peaks in week 13 with 7100 yards/meters of swimming, 6 hours of cycling, and 5 hours of running.

Before starting this plan, you should have a solid base of 7-8 average training hours for the past 4+ weeks, including interval work at threshold effort levels, so that you are prepared for the training volume and intervals in week 1 of the plan. Additionally, within 2-4 weeks of starting this plan, you should set or update your pace, power, and/or heart rate training zones to ensure that you have current numbers for all zones in each sport. For more on this, see How to Establish Training Zones.

80/20 triathlon training plan method

The plan uses pace (swim and run) or power (bike) along with rate of perceived exertion (RPE) to guide target effort levels for all workouts. The chart below summarizes the training zones that will be used in the plan along with corresponding pace/power and RPE. Your base swim pace, bike FTP, and run 5k pace can be assessed in week 1 of the plan if you need to set or update your zones.

Training plan key

• WU = warm up
• PS = prep set
• MS = main set
• EZ = easy (Zone 1 for swim and run, 50% of FTP for bike)
• CD = cool down
• 5” = 5 seconds
• 5’ = 5 minutes
• RI = rest interval

Repeated workouts

A 16-week 80/20 triathlon training plan for 70.3

Week 1

Week 2

Week 3

Week 4

Week 5

Week 6

Week 7

Week 8

Week 9

Week 10

Week 11

Week 12

Week 13

Week 14

Week 15

Week 16