The Science of 80/20 Training

It’s easy to assume that the world’s best runners and triathletes spend most of their time pushing their physical limits to the brink—but they don’t.

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It’s easy to assume that the world’s best runners and triathletes spend most of their time pushing their physical limits to the brink—but they don’t. Here, 80/20 Triathlon author Matt Fitzgerald and David Warden breaks down the basic of the 80/20 method of triathlon training.

Although scientists did not create 80/20 training, science has proven that the intensity balance favored by today’s elite endurance athletes yields superior results for athletes of all levels compared to other, more intense methodologies. Science has also helped explain why the 80/20 system is more effective.

The Recipe for Endurance Fitness

Triathlon training is like a cake. If you want to bake a cake that tastes really good, you must first select the right ingredients and then you must combine these ingredients in the right proportions. In triathlon training, the ingredients are different types of workouts that target a range of exercise intensities. To maximize the fitness you gain from your training, you need to do some workouts that target low intensity, others aimed at moderate intensity, and still others that focus on high intensity. As for proportions, the best results are achieved when low intensity accounts for 80 percent of total training time and moderate and high intensity together account for the remaining 20 percent. This is the recipe for endurance fitness.

Stretching our metaphor a little further, suppose a child asked you to help her bake a cake and she proposed that the two of you proceed by identifying the best possible ingredient and making the cake out of that one ingredient. Unless you are an even worse cook than we are, you would probably explain to the child that what makes a cake better than any single ingredient that goes into it is how the flavors of all the ingredients combine.

Again, triathlon training is similar. In the popular media and general fitness culture, low-intensity and even moderate-intensity exercise get little respect, while high-intensity workouts are constantly hyped. Magazine and Internet articles, fitness club franchises, and television advertisements for exercise equipment suggest that high intensity is simply “better” than low and moderate intensity. Implicit in these comparisons is the idea that low-, moderate-, and high-intensity exercise all affect the body in fundamentally the same ways but the effects of high intensity are bigger.

In reality, different intensities contribute to fitness in diverse ways, just as individual ingredients contribute distinct flavors to a cake. While there aren’t many “experts” who recommend that endurance athletes include only one ingredient—namely, high intensity—in their training recipe (although there are some), the popular notion that high intensity affects the body in the same way as low and moderate intensity, only more so, does incline many triathletes to undervalue and underutilize low and moderate intensities. A glance at the science shows why all three intensity ranges are essential ingredients in the recipe for endurance fitness.

Low Intensity
The upper limit of the low-intensity range is the ventilatory threshold (VT), which falls at or near 78 percent of maximum heart rate in the typical person who engages in regular exercise. But the low-intensity range also has a bottom end, which falls around 60 percent of maximum heart rate. Exercising at intensities somewhat below this level does offer health benefits, but it does not produce the kinds of training effects that triathletes seek. When we refer to low intensity, we’re not talking about taking the dog out for a leisurely stroll in the neighborhood but about swimming, cycling, and running at efforts that fall within the range of roughly 60 to 77 percent of maximum heart rate.

So just what are the training effects associated with swimming, cycling, and running at low intensity? One is improved aerobic capacity. Measured as VO2 max, aerobic capacity is the body’s ability to extract oxygen from the atmosphere, transport it to the working muscles, and use it to release energy from metabolic fuels, powering muscle contractions. Low-intensity exercise stimulates a variety of physiological adaptations that elevate aerobic capacity. These changes include a stronger heart that pumps more blood per contraction, increased blood volume, more red blood cells, greater capillary density in the muscles, heightened activity of aerobic enzymes, and accelerated production of mitochondria, the little factories within muscle cells where aerobic metabolism occurs.

Another benefit of low intensity is improvement in the ability of the muscles to use fat as fuel. In essence, this gives athletes a bigger fuel tank to draw upon during races, enabling them to go faster and farther without hitting the wall. The capacity to burn fat at a high rate is especially important in longer triathlons, and low-intensity workouts do the best job of enhancing this capacity.

Fatigue resistance is further enhanced by low-intensity exercise through brain-based mechanisms. During exercise, the brain works just as hard as the muscles, because it is the brain that drives the muscles, after all. Hence, the brain gets tired just as the muscles do whenever an exercise effort continues to the point of exhaustion. But muscle fatigue and brain fatigue contribute to exhaustion in different degrees at different intensities. If you swim, bike, or run to exhaustion at a very high intensity, muscle fatigue is greater than brain fatigue. But if you exercise to exhaustion at a lower intensity, a process that takes much longer, it is the brain that is more fatigued at the end.

This is important, because improvements in fatigue resistance come from exposure to fatigue. Just as you must tire out your muscles so as to make them more resistant to tiring out in future workouts, you must fatigue your brain to enhance its fatigue resistance. By exposing the brain to higher fatigue levels, prolonged training at low intensity improves fatigue resistance in the brain more than shorter workouts at high intensity do. And while these changes may have the greatest benefits for longer races, it is likely that they have some effect on performance in endurance races of all distances.

The brain also plays a crucial role in regulating and improving technique in the water, on the bike, and on foot. Every single time you execute a running stride, a freestyle swim stroke, or a pedal rotation on your bike, your brain and muscles are communicating, your brain using feedback from your muscles to look for little shortcuts that will allow you to complete the next stride or stroke or rotation with less energy. This process happens unconsciously and automatically, and it never ceases. Intensity doesn’t matter. What matters is repetition. Because it takes a lot longer to get tired at low intensity than it does at high intensity, low-intensity workouts offer far greater opportunity to practice and refine technique. Case studies involving elite endurance athletes such as marathon world record holder Paula Radcliffe indicate that while VO2 max typically peaks in the early twenties in these athletes, efficiency continues to improve for many years afterward, a trend that is associated with accumulated low-intensity training and is largely responsible for improved race performances.

Moderate Intensity
The moderate-intensity range, as it relates to endurance training, falls roughly between 78 and 92 percent of maximum heart rate in a typical fit individual. As you have learned already, most triathletes spend way too much time swimming, cycling, and running in this zone. But the solution to the problem is not to avoid moderate intensity altogether. That’s because the moderate-intensity range overlaps with race intensity at most triathlon distances.

Common sense suggests you that you should not go into a race without having done any training at the speeds you hope to sustain within the race, and science backs up this hunch. To a large extent, the fitness you gain from training at any single intensity—low, moderate, or high—is generalized to all intensities. You only have one heart, after all, and if you strengthen it exclusively through exercise at a single intensity, it will function better at other intensities (though not as well as it would if you balanced your intensities like the pros). But research has shown that fitness gains are also intensity-specific to some degree. Training at any single intensity tends to improve metabolic and biomechanical efficiency at that intensity more than any other. This makes moderate-intensity exercise an indispensable component of optimal triathlon training.

High Intensity
It is all too easy to caricature the 80/20 method as anti–high intensity, but it is not. The elite endurance athletes who discovered and model this method train at high intensity every week, and science explains why they are smart to do so. As we noted in our discussion of the benefits of low intensity, both low intensity and high intensity increase aerobic capacity, though not entirely through the same mechanisms. For this reason, it is impossible to truly maximize your aerobic capacity without including high-intensity exercise in your training.

The boundary between moderate and high intensity falls at the respiratory compensation point, a threshold that corresponds to roughly 93 percent of maximum heart rate in the typical person who exercises regularly. Swimming, cycling, and running at or above the respiratory compensation point generates large amounts of lactate, which not only serves as an energy source during exercise but also signals certain genes after exercise to increase the body’s production of mitochondria, those little intracellular factories where oxygen is used to break down metabolic fuels. Through lactate and other means, high intensity boosts aerobic capacity in ways low intensity doesn’t. If you want to gain the greatest amount of fitness from the time you invest in training, you would be as remiss to leave high intensity out of your training recipe as you would to neglect low or moderate intensity.

Getting Started with 80/20 Training

Effective triathlon training requires planning. Whether you’re new to the sport or you’re a seasoned age-group awards chaser, you will achieve greater improvements in fitness and performance if you follow a well-designed training plan than you will if you wing it. Creating a triathlon training plan is not rocket science (trust us: we do it every day, and we’re not rocket scientists!), but it does require an understanding of not only the 80/20 Rule of intensity balance but of other proven training principles and practices as well.

Only a small fraction of triathletes choose to create their own training plans, the rest preferring to leave this job to the experts. You may share this preference, in which case you will want to start your 80/20 triathlon journey by following one of the ready-made plans you’ll find in 80/20 Triathlon. But even if you do, you will still benefit from learning the principles and best practices of training plan design, as it will help you make good decisions when you need to modify or depart from your plan due to fatigue, soreness, or other factors, and will give you the option to begin coaching yourself down the road. While the 80/20 approach provides a simple guideline for balancing the intensity of training, there’s a bit more to the process of creating an effective triathlon training program. There are six steps to creating your own custom 80/20 triathlon training plan:

Step 1: Define your training cycle.

Step 2: Schedule recovery weeks.

Step 3: Create a default weekly workout schedule (or microcycle).

Step 4: Plan your peak training step cycle.

Step 5: Plan your first training week.

Step 6: Fill in the rest of your schedule.

Don’t let perfect be the enemy of good when you sit down to create a training plan for yourself. There’s no such thing as a perfect plan, but if you follow the procedure discussed in 80/20 Triathlon, your plan will be good enough. And your next one will be even better. When we work with individual athletes, we never fail to find ways to train them more effectively in the next cycle based on how they responded to the training we prescribed in the previous one. Over time, we move steadily toward perfection without ever attaining it. By learning from your body’s response to your own training plans and applying the lessons you pick up in each subsequent plan, you will do the same.

Adapted from 80/20 Triathlon: Discover the Breakthrough Elite-Training Formula for Ultimate Fitness and Performance at All Levels by Matt Fitzgerald and David Warden. Copyright © 2018. Available from Da Capo Lifelong Books, an imprint of Perseus Books, LLC, a subsidiary of Hachette Book Group, Inc. Find the book now at

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