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The 80/20 Rule of Training Intensity

Contributor: Matt Fitzgerald     Category: Training

If you ask any running coach to name the most common mistake that runners make in their training, he or she will probably say, “Running too hard on easy days.”

Science backs up this observation. In a 1993 study, for example, researchers at Arizona State University asked a group of recreationally competitive runners to describe their training. On average, these runners claimed to do three low-intensity runs, one moderate-intensity run, and 1.5 high-intensity runs per week. But when the researchers monitored the runners’ heart rate through a week of training, they found that they actually did only 46 percent of their weekly training at low intensity and another 46 percent at moderate intensity.

In short, most of the training that runners think they are doing at low intensity is in fact done at moderate intensity. I refer to this phenomenon as “intensity blindness.”

Spending nearly half of one’s total training time at moderate intensity wouldn’t be a problem if this were an effective way to train, but it’s not. Research has shown that elite endurance athletes in all disciplines, from running to rowing, do 80 percent of their training at low intensity and the remaining 20 percent at moderate and high intensities. Exercise scientists believe that this universal pattern is the result of generations of trial and error conducted at the highest levels of the various endurance sports. Virtually every way of balancing training intensities has been tried, but only the 80/20 balance has survived, because it works best.

But what about nonelite runners like us? Studies have also demonstrated that runners and other endurance athletes of all experience and ability levels improve most when they follow the “80/20 Rule” of intensity balance. A 2014 study led by Jonathan Esteve-Lanao of the European University of Madrid found that club-level runners who obeyed the 80/20 Rule improved their 10K races times by twice as much as their peers who followed a 50/50 intensity split. What this means is that most runners have to slow down to get faster!

Breaking out of the moderate-intensity rut and taking advantage of 80/20 training is a three step process:

Step 1. Find your intensity zones.

In order to spend 80 percent of your training time at low intensity and 20 percent at moderate and high intensities, you need to know what low, moderate, and high intensities are for you. I’ve developed a simple calculator that makes it easy to determine your personal training intensity zones. It is a five-zone system in which Zones 1 and 2 correspond to low intensity, Zone 3 is moderate intensity, and Zones 4 and 5 are high intensity.

Step 2. Plan 80/20 training weeks.

This second step is a simple math game. For example, if you train 5 hours per week, that’s 300 minutes. Eighty percent of 300 is 240, or 4 hours. Here’s how a 5-hour training week with 1 hour of moderate- and high-intensity training might look:

LI = Low Intensity, MI = Moderate Intensity, HI = High Intensity

Step 3. Monitor and control intensity in workouts.

It’s one thing to plan the perfect 80/20 week, another to actually do it. If you’re like many runners, you already intend to do most of your running at low intensity, but when you get out on the road, you do something else—without even realizing it. Fixing this problem requires that you actively monitor your intensity throughout every run and staying in the targeted zones.

Being disciplined in this way can be surprisingly difficult at first. But if you take a leap of faith and follow through with your plan to slow down, your intensity discipline will be well rewarded. The first thing you may notice is that you’re less fatigued from day to day. You’ll also find that you are able to train faster and more comfortably in higher-intensity workouts.

Not to mention on race day!