Intensity is one of the most vital aspects of training for distance runners. The concept simply involves measuring how hard you’re running related to how hard you’re capable of running.

Intensity is usually classified into three different areas: low, moderate and high. Exercise experts put the level between low and moderate-intensity at the first ventilatory threshold, the point where you have to start breathing heavier. This is often a bit slower than the lactate threshold. The level between moderate and high-intensity training is at the second ventilatory threshold, which is slightly higher than the lactate threshold.

These intensity zones affect every runner’s fitness differently. Each training plan directs workouts of various distances or times in each level. The main question is: What is the optimal balance of time spent at low, moderate and high-intensity intervals for runners who seek maximum fitness?

Answering this question relies on comparing the effects of different intensity practices on real-world running performance. Studies are difficult to conduct, and only a few researchers have completed experiments that have come close to finding an optimal balance. One study has shown that runners of all abilities and experience seem to improve the most when they complete approximately 80 percent of their training at low intensity and 20 percent at moderate and high-intensity.


The 80/20 Rule

In the early 2000s, American exercise scientist Stephen Seiler researched how elite endurance athletes really train. He found a consistent pattern between world-class cyclists, Nordic skiers, runners, rowers, swimmers, and even triathletes. They all completed approximately 80 percent of their training low intensity. All these athletes trained at the same level because this particular balance of training intensities annihilated the others and it did a better job of improving aerobic capacity.

The popularity of the 80/20 training approach isn’t conclusive proof of maximum fitness, but it is more effective than alternatives for athletes in these abilities. Seiler searched for evidence and with Jonathan Esteve-Lanao of the European University of Madrid. Together, they conducted a series of experiments. One of the studies involved 12 high-level male running subjects. Half of the subjects were placed on a training program with 80 percent of the running at low intensity and 20 percent at moderate to high-intensity. Thes other group conducted 65 percent of their training at low intensity and 35 percent at moderate to high-intensity. Both groups averaged the same mileage per week, but the runners in the 80/20 group lowered their times 36 seconds more than those in the 65/35 group.


Training with the Right Intensity Ratio

Since the 80/20 method clearly works best and is used by many professional athletes, why do so many competitive and recreational runners only complete half their training at moderate intensity or faster? Seiler believes that low-intensity is much broader for elite runners and it’s easier for them to stay under the moderate threshold. Learning how to escape the moderate-intensity level and access the 80/20 rule can be achieved in three steps:

  1. Learn the Zones

    First, learn the difference between all three intensity zones, and the borders between low and moderate intensity. Online you can find tables for heart rates, breathing and effort that will help runners distinguish between the three zones. It’s best to avoid monitoring your pace for easy runs, since pacing data makes runners want to go faster. Heart rate and perceived effort are better tools.

  2. Plan your Training

    The next step is to map out a training plan that upholds the 80/20 rule. Runners can do this with simple math. If you run 5 hours each week, that’s 300 minutes. Eighty percent of 300 is 240 or four hours. From here, runners can determine a 5-hour training week with 1-hour of moderate and high-intensity training.

  3. Execute your Running Strategy

    Most people don’t follow the 80/20 rules, even though they plan to. Often, they start running at moderate intensity without even noticing it. Plan to warm up slowly. Once you start feeling warm, start running faster and learn how to discipline yourself. The effort has to be easier than you believe it should be. What is really moderate effort is a pace you think is easy. When you feel like your run is too easy, run at an even slower pace. Practicing this restraint can be difficult at first. As you slow down, your intensity discipline will be rewarded and you may find yourself less tired each day and that you’ll be more comfortable in higher intensity workouts.