80/20 Intensity Balance – 80/20 Endurance

80/20 Intensity Balance

In my late teens and early twenties I was a meathead, visiting the gym several times a week to toss around heavy things. At some point during this period I developed a hypothesis that there are both relative and absolute components to how weightlifters perceive resistance. Suppose you are able to bench press 200 pounds, and your friend is able to bench press 300 pounds. Does this mean that benching 200 pounds feels exactly the same to you as benching 300 pounds does to your friend? My hypothesis said no. While both of you will feel that your muscles are working at maximal capacity (relative component), your friend will perceive his weight as being heavier—because it is heavier! On a purely physical level, your friend’s bones, ligaments, tendons, and myofascia will be under 300 pounds of stress, which is objectively greater than 200 pounds of stress, so why wouldn’t your brain perceive that?

I’m not 100 percent sure this hypothesis is correct, but I’m 99 percent sure. What is certain is that the endurance equivalent of my weightlifting hypothesis is true. Simply put, athletes experience intensity and speed differently. If your maximal sprint speed, say, is 18 mph and your friend’s maximal sprint speed is 21 mph, you feel you’re working as hard at 18 mph as your friend feels at 21 mph, and yet your friend will perceive that he’s moving faster—just as you yourself would do if you sprinted on a decline and got up to 21 mph. This is an incontestable fact.

What is not an incontestable fact is my further speculation that runners of all abilities want to run between 7:00 and 8:00 per mile in their bread-and-butter aerobic runs. I believe this is the absolute speed that feels about right for most runners when they’re just out for a jog. This is why elite runners seldom go much faster than 7:00/mile in their easy runs even though the intensity associated with this pace is laughably low for them, and it’s why middle-of-the-pack runners seldom run much slower than 8:00/mile in easy runs even though the pace associated with this pace is too high for easy runs. I’m exaggerating a bit, but studies have shown that fitter runners do tend to run at a lower intensity on their easy days than less-fit runners. So what we see is a compression toward the middle in terms of easy-run pacing, with slower runners running faster than they should and faster runners running slower than they could without violating the purpose of this type of run.

If my conjecture is correct, it explains why slower runners so often struggle initially to stay in Zone 2 when adopting the 80/20 training method. Although Zone 2 is technically easier than the Zone X intensity at which the majority of slower runners do their easy runs, there is something in the bodies of all runners (most, anyway) that prefers the absolute pace range of 7:00-8:00 per mile. I see this phenomenon as roughly analogous to the almost universal human preference to run rather than walk when the target pace is 13:00 per mile even though walking is more energetically efficient at this pace.

I confess that I have little patience for runners who adhere poorly to the 80/20 requirement that they ease back on their easy runs. I want to grab the complainers by the lapels and ask, “Do you trust that slowing down in your easy runs will benefit your fitness? Yes? And is it physically possible for you to go slower in this runs even though it feels kind of weird? Yes again? Then just do it and stop complaining!”

Correction: I used to have little patience for the complaints of slower runners who struggled to hold themselves back to Zone 2 in easy runs—until I myself became a slower runner!

When I developed long covid in October 2020, I was far from slow. Having recently run 33:25 for 10K in a solo time trial on a wheel-measured route, I was trying to decide between two options for my next goal: 4:49 for the mile or 15:59 for 5K on the track, both times within shouting distance of PR’s set decades earlier. Little did I know at the time that within four months I would be forced to stop running altogether and that I wouldn’t run again for another 23 months.

I am now 51 years old and woefully out of shape, but I am more or less healthy. For six weeks in early 2023 I was cautiously progressing on a self-devised regimen of every-other-day walk/runs. What’s funny is that I couldn’t seem to make myself jog much slower than 9:00 per mile (at 7,000 feet of altitude) in the running segments of these sessions. Both my heart rate and breathing rate suggest I was well above Zone 2 at this pace, and yet I persist.

Here’s how I justify my hypocrisy: First, while adhering to an 80/20 intensity balance is the optimal way to build aerobic fitness, it is not the only way. Though inefficient, my regimen was working. One morning I ran 3 x 8:00 at an average pace of 8:45 per mile and felt pretty good, something I could not have done at the start of this process. Furthermore, adhering to an 80/20 intensity balance is only really necessary when you’re trying to maximize your fitness, and that was not my goal. I was just relishing the simple ability to do something I love that I couldn’t do for a very long time.

Barring setbacks, I expect to continue on my present course until I’m fit enough to run an hour straight. My pace will continue to drop as I gain fitness, though not as swiftly, such that by the time I reach the one-hour target, I will be running in Zone 2, just like the old days. Then I’ll weigh my options.

In the meantime, the experience has given me greater empathy for runners who struggle to force themselves to stay in Zone 2 on easy runs. Whether or not my theory of a universally preferred jogging speed is accurate, I have a better appreciation for the impediments to slowing down. A better man than I would not have needed to choke down a big old slice of humble pie to gain this appreciation, but although I’m not above the occasional hypocrisy, one thing I’ll never do is claim to be a better man than I am.

There’s a good chance you came across the following headline, or another one like it, a couple of weeks back: “Too Much High-Intensity Exercise May Be Bad for Your Health.” These click-baiting newsflashes referred to a new study out of Sweden’s famed Karolinska Institute that looked at the molecular and metabolic effects of a HIIT program in previously casual adult exercisers. Eleven unlucky volunteers were subjected to an utterly brutal regimen that ramped up to five HIIT sessions per week within three weeks, each session comprising a mix of four- and eight-minute intervals performed at maximum intensity. The consequences of this diabolic torture program included severely compromised mitochondrial function and erratic blood sugar levels.

My first thought on reading the above-referenced headlines was duh. In more than 20 years of serious endurance training I never attempted anything approaching the savagery of what those poor, unsuspecting guinea pigs underwent in a state of woeful unpreparedness. I know with 100 percent certainty that the same routine would have utterly steamrolled me even if I’d gone into it at my absolute lifetime peak of fitness. Hilariously, though, the negative effects seen in this study’s subjects were referred to in one article as “unexpected.” Is the popular media really that clueless? I guess so!

Coincidentally, these shockingly predictable fresh findings from the Karolinska Institute came fast on the heels of a highly complementary recent study by scientists at the University of Guelph. For this experiment, 23 overweight, sedentary men were separated into groups, one of which did three HIIT workouts per week on stationary bikes while the other did five longer, low-intensity workouts. Versions of this format had been used in many prior studies, but what was different this time was that the two exercise programs were not matched for total workload (i.e., total energy expenditure).

The purported rationale for matching workloads in past research was fairness. The scientists conducting these experiments wanted to see whether low-intensity or high-intensity exercise was more “effective,” and in their minds this required that total energy expenditure be held equal. In my mind, however, the format unfairly disadvantaged low-intensity exercise, for the thing about HIIT is that a little goes a long way, so of course it’s going to seem more effective if a little HIIT is compared against a little low-intensity exercise, which only has a chance to really shine in large amounts, which (unlike large amounts of high intensity) are well tolerated by the human body.

Anyway, in the new Guelph study, common sense prevailed at long last, and the low-intensity and high-intensity programs were balanced in a more realistic way. And wouldn’t you know, the low-intensity program kicked the HIIT program’s ass in terms of health benefits, yielding bigger improvements in body composition, lipid metabolism, blood pressure, and blood sugar regulation.

I’m now waiting for it to finally cross the minds of exercise scientists to investigate the health effects of mixing together workouts of different intensities as we endurance athletes do. Up to this point, researchers interested in the health effects of aerobic exercise have focused entirely on trying to figure out which intensity is “best,” but to me that’s a little like trying to determine which of a baseball pitcher’s five pitches is his best pitch with a view toward having him throw only that pitch going forward. What would happen in this scenario, of course, is that hitters would know exactly what was coming their way every time the pitcher wound up, and all of a sudden his best pitch wouldn’t be so effective anymore!

Okay, that’s a poor analogy, but you get my point. Sometimes things work better in combination than they do in isolation. And we already know this is true of exercise intensities when they are assessed according to their effects on fitness. Specifically, we know that an exercise program comprising an 80/20 balance of low intensity and moderate/high intensity yields greater gains in endurance fitness and performance than a program consisting entirely (or even mostly) of work at either low intensity or moderate/high intensity.

Would an 80/20 program also yield greater health benefits than the alternatives? It seems likely to me that it would. It’s been shown, for example, that 80/20 training yields greater improvements in aerobic capacity than does any other way of balancing intensities, and we know that aerobic capacity is a strong predictor of health in old age and longevity.

What are the chances, though, that 80/20’s factual superiority will result in its popularization beyond the endurance community? Rather slim, I would imagine. One of the reasons HIIT became so popular is that interval sessions are sexier than slow-and-steady aerobic workouts. Can you picture a bunch of folks gathering for a group fitness class where the instructor pedals nice and easy for 80 minutes straight and invites everyone else to do the same? Yeah, me neither. But one can dream.

I am often asked if the 80/20 rule of intensity balance applies to athletes who train at very low volumes. It’s a fair question. We know that low-intensity exercise doesn’t do a lot of good in small amounts, whereas high-intensity exercise does. It is plausible therefore that, below a certain volume threshold, doing less than 80 percent of one’s training at low intensity will yield better results than sticking to the 80/20 rule.

A new study by Luca Festa of the University of Verona and colleagues addresses this question—sort of. The subjects were recreational runners with at least four years of experience. For eight weeks, half of them followed a “polarized” training program in which 77 percent of training was done at low intensity, 3 percent at moderate intensity, and 20 percent at high intensity, while the other half maintained a 40/50/10 intensity split (“focused endurance training”). Volume was adjusted to ensure that the total training load (intensity and volume combined) was equal for the two groups. This required runners in the polarized group to run slightly more than runners in the focused endurance group, though volume was quite low in both groups, averaging out to 3.73 hours per week and 3.1 hours per week, respectively.

Physiological and performance measures were taken on all of the subjects before and immediately after the eight-week training intervention. The table below summarizes the results.

Polarized Focused Endurance
Fat Mass -12.7% -8.6%
VO2max +1.2% +0.9%
Velocity at VO2max +3.2% +4.0%
Running Economy +5.3% +7.0%
Average Velocity in 2K time trial +3.5% +3.0%

As you can see, they’re kind of a mixed bag. The polarized group saw bigger improvements in body composition, VO2max, and (what is arguably the only result that matters) time-trial performance, while the focused endurance group experienced bigger gains in running economy and velocity at VO2max. None of these differences was judged to be statistically significantly, however, so Festa’s team concluded that “Focused Endurance Training obtains similar improvements [as] Polarized Endurance Training[,] saving 17% of training time in recreational runners.”

There you have it: 80/20 training is a waste of time. You get equal results in less time by doing half of your training at moderate intensity, which is precisely the opposite of what 80/20 advocates like me tell athletes not to do.

But wait—there’s another interpretation. Remember the commonly asked question I mentioned at the top of this article? We started out with the premise that it is likely that, below a certain threshold of training volume, an 80/20 intensity balance might not yield optimal fitness benefits. The results of Festa’s study suggest that this threshold is very low indeed, if indeed it exists at all. Members of the polarized group and the focused endurance group ran just 32 minutes and 27 minutes per day, respectively, during the eight-week study period, and improved by roughly equal amounts. So it’s safe to say that you would have to run less than 25 minutes a day, on average, for a more intense training approach to possibly produce better results than the 80/20 method, emphasis on “possibly.”

It’s also worth drawing attention to the fact that the only performance test included in Festa’s study was a 2 km time trial. That’s pretty short. Why 2 km? Because Festa and his colleagues wanted to set up the focused endurance group for success, that’s why! Clearly, a short performance test was going to give the group doing shorter runs the best chance of equaling the improvement of the other group. Even then, though, the polarized group improved slightly more. And although the difference was statistically significant, meaning it could have happened by chance, I’d be willing to bet that if this same experiment were rerun 100 times, the polarized group would improve more with a frequency that exceeded chance, hinting at the beginning of a trend that would only grow as the distance of performance tests increased.

Furthermore, although Festa’s study itself was quite short, its brevity was appropriate in the sense that it doesn’t take long for a training program of such low volume to yield the full measure of its potential benefits. In other words, had the experiment lasted longer, it’s unlikely that either group would have improved much more. But suppose you were to actually follow one of the two programs involved in this study, getting whatever benefit you could squeeze out of it in 8-10 weeks, and then decided that you wanted to improve more going forward.

Here’s what would happen: If you were on the focused endurance plan and you proceeded by gradually increasing the volume of training you did at the same 40/50/10 intensity ratio, you would gain fitness at a gradually decreasing rate for a little while before reaching a point of negative returns at a still fairly modest volume level. That’s because any training done above the first ventilatory threshold—whether moderately intense or highly intense—is significantly more stressful to the body than training done below the VT1, and on this program you’re doing 60 percent of your total running above that threshold. Festa’s team collected data on perceived effort from their subjects but did not report it, and again, I’d be willing to bet that members of the focused endurance group perceived their training to be harder than members of the polarized group perceived their training to be, even though mathematically their training loads were equal.

But if instead you went through the same process on the 80/20 program, you would continue to improve for a very long time, albeit at a diminishing rate, not reaching the point of negative returns until you’re doing a ton of running. And that’s because training below the first ventilatory threshold is so gentle on the body that even the average athlete can handle (and benefit from) massive amounts of it. I would only add that, whereas in this study almost all of the 20 percent of training done above the VT1 was done at high intensity, a runner training at ever-increasing volumes would be wise to gradually shift minutes from the high-intensity bucket to the moderate-intensity bucket as volume grew.

Festa and his colleagues admit that it is a well-established fact that an 80/20 intensity balance provides the best possible results for athletes who train a lot, writing, “several studies have shown that it allows them to achieve greater improvements in performance,” and that “this distribution is necessary for athletes who perform a large volume of training, to prevent overtraining or steady state of performance.” What this new study shows is that the 80/20 approach is also at least as effective as a more intense training approach at a very low training volume of around 30 minutes a day. In other words, the title of this article is a joke.

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