Intensity. It’s one of the most fundamental and important variables in the training of distance runners. In layperson terms, intensity is simply how hard you’re running relative to how hard you’re capable of running.
Intensity can be classified into three general zones: low, moderate and high. Exercise scientists place the border between low and moderate intensity at the first ventilatory threshold, the point where you have to start breathing harder, which is a bit slower than lactate threshold. The border between moderate and high intensity falls at the second ventilatory threshold, which is slightly higher than the lactate threshold.
Each intensity zone affects a runner’s fitness differently. Every training plan prescribes workouts of various distances or times in each zone. So here’s the key question: What is the optimal balance of time spent at low, moderate and high intensity for runners seeking maximum fitness?
The only way to answer this question definitively is to rigorously compare the effects of different intensity distributions on real-world running performance. Such studies are difficult to do, so few have been done, however, a handful of researchers have completed experiments that have gone a long way toward pinning down this optimal balance.
Specifically, these studies have shown that runners of all ability and experience levels seem to improve the most when they do approximately 80 percent of their training at low intensity and 20 percent at moderate and high intensity.
A look at training logs of runners of different abilities shows that nearly all elites follow the “80/20 rule,” but most other runners don’t—a discrepancy that is familiar to coaches who work with both elite and recreational runners. “You would assume that maybe most people wouldn’t train hard enough,” says Pete Rae, who coaches post-collegiate runners and Olympic hopefuls and hosts running camps for recreational runners at ZAP Endurance in Blowing Rock, North Carolina. “But what I find with the overwhelming majority of adults who come to our camps is that they tend to do their daily runs too hard.”
Research confirms this observation. According to a study by Muriel Gilman at Arizona State University, the typical adult competitive runner does only 46 percent of his or her training at low intensity and another 46 percent at moderate intensity. Chances are you, too, are caught in the “moderate-intensity rut” without realizing it. If so, then the surest way for you to race faster is to train slower.
The 80/20 Rule
In the early 2000s, Stephen Seiler, an American exercise scientist based in Norway, embarked on a mission to determine how elite endurance athletes really train. He found a remarkably consistent pattern: World-class cyclists, Nordic skiers, rowers, runners, swimmers, and triathletes all did approximately 80 percent of their training at low intensity.
Seiler knew it was very unlikely that this pattern was the result of either random coincidence or copycatting. The only explanation that made any sense was that this particular balance of training intensities had annihilated others (such as the interval-heavy approach that was dominant in the 1950s) because it did a better job of increasing aerobic capacity, a goal shared by elite athletes in all endurance disciplines.
The ubiquitous reliance of elite endurance athletes on the 80/20 training approach does not itself constitute conclusive proof that it is more effective than the alternatives for athletes of all abilities. In search of such proof, Seiler collaborated with Jonathan Esteve-Lanao, a club running coach and an exercise scientist at the European University of Madrid, to conduct a series of experiments.
One of these studies involved 12 high-level male runners from Esteve-Lanao’s club who had clocked 10K times between 30 and 35 minutes. Half of the subjects were placed on a training program that required them to do 80 percent of their training at low intensity and 20 percent at moderate and high intensity for five months. The other six runners did 65 percent of their training at low intensity and 35 percent at moderate and high intensity. Both groups averaged 80 to 88 kms of running per week. All 12 runners completed 10.4K time trials before and after the training period. On average, the runners in the 80/20 group lowered their times 36 seconds more than those in the 65/35 group.
Intrigued by these results, Seiler and Esteve-Lanao conducted a follow-up study that was designed to determine whether 80/20 training also worked better for slower runners who trained less. This study involved 30 runners who ran fewer than 65 kms per week and had 10K times of just under 40 minutes. Half of the runners followed the 80/20 rule while the other half maintained a 50/50 split (as many adult competitive and recreational runners do). After 10 weeks, the runners in the 50/50 group had lowered their 10K times by an average of 3.5 percent, while the runners who followed the 80/20 rule most faithfully improved by double that amount.
In future research, Seiler and Esteve-Lanao hope to learn why an 80/20 intensity balance is optimal. Existing evidence suggests that training above the ventilatory threshold is just too stressful to be effective in large amounts, whereas low-intensity training has a much higher point of diminishing return. A 1999 study by Veronique Billat, a professor of Sport Sciences at the University of Lille, France, found that middle-distance runners who did three easy runs and three interval runs per week for four weeks exhibited higher levels of stress hormones and a decline in VO2max compared to when they did five easy runs and one interval run per week for four weeks.
How to Escape the Moderate-Intensity Rut
If the 80/20 method clearly works best and is practiced by many (if not most) elite runners, why do so many competitive and recreational runners complete approximately half of their training at moderate intensity or faster? Seiler suspects one reason is that the low-intensity zone is much broader for elite runners, hence making it easier to stay below the moderate threshold.
For example, a 2:10 marathoner is likely to be below the first ventilatory threshold when running at 5:40 per km, whereas a 3:30 marathoner may be above this threshold already at 8:05 per km. Take that example even further to a 10-minute km runner (which yes, is more common than you think and still qualifies you as a runner!), and his or her low-intensity zone might end up being a run-walk.
Escaping the moderate-intensity rut and falling in line with the 80/20 rule is a three-step process.
1. Learn Your Zones
Step one is to learn the difference between the three intensity zones, especially the line between low and moderate intensity. The table below provides guidelines for heart rate, breathing, and perceived effort that will help you distinguish the three zones from one another.
Why no guidelines for pace? “It’s best not to monitor pace in easy runs,” says Bobby McGee, a veteran coach of runners and triathletes. “Pace data has a way of making runners want to go faster. I find that perceived effort and particularly heart rate are much better tools for holding runners back.”
2. Plan Your Training
The next step is to map out your training so that it adheres to the 80/20 rule. This is a simple math game. For example, if you run 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:
3. Execute Your Plan
The final step is execution. It’s one thing to plan the perfect 80/20 week and another to actually do it. If you’re like most adult competitive or recreational 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. You warm up slow; you start feeling good, you start running faster; (oops) you end the run having done a moderate- or high-intensity effort. Fixing this problem requires what Seiler calls “intensity discipline.”
“The effort has to be lower than you think it should be because you’ve essentially made abnormal normal,” says Greg McMillan, exercise scientist, veteran running coach, and author of YOU (Only Faster). “What is really a moderate effort, you’re calling easy. So when you feel like you’re running easy, run easier.”
Practicing such restraint 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,” Rae says. “You’ll also find that you are able to run faster and more comfortably in higher-intensity workouts.”
Not to mention on race day.