HIIT – 80/20 Endurance

You’ve probably heard of the book 80/20 Running, perhaps even read it. But did you know that the original working title of this book was A High-Mileage Manifesto? I started writing it in 2013, a time when HIIT mania was in full bloom, CrossFit Endurance was making waves, and Run Less, Run Faster was the top-selling training guide for runners. Dismayed by these and other influences, I decided to push back in the best way I knew. It was only when I realized that the average runner can’t benefit from running more until they’ve first balanced their training intensities correctly—shifting from the typical 50 percent moderate-intensity routine to the 80 percent low-intensity approach of the elite—did A High-Mileage Manifesto become 80/20 Running.

Despite this evolution, I remain convinced that exercising a lot is a proven best practice in endurance training that not enough athletes at the nonelite level actually practice. Scientific support for this position keeps coming. The latest evidence arrives in the form of a study published in the European Journal of Applied Physiology. Japanese researchers surveyed 587 runners (all male, unfortunately) about their training prior to their participation in the 2017 Hokkaido Marathon. Intensity data were not included in this particular study. The researchers were specifically interested in identifying links between various volume-related parameters and marathon performance—and they found them.

Among runners who trained with equal frequency, there were significant correlations between monthly training volume, average run distance, long run distance, and marathon time. In other words, given two runners who each trained five times per week, the one who packed more miles into these runs tended to perform better on race day. Interestingly, though, when the researchers compared runners at different levels of monthly volume, there were no correlations between training frequency, average run distance, long run distance, and marathon time. This suggests that monthly volume matters a lot, and how one achieves it matters less. But it does matter some, for when the researchers looked at runners who had the same average run distance or long run distance, strong correlations were found between these variables and monthly volume and marathon time.

On the basis of their findings, the researchers concluded, “These results indicate that monthly training volume is the most important factor in predicting marathon time and that the influence of monthly training volume is only significant if the running distance per workout exceeded a certain level.” The lesson I draw from this study as a coach is that, if you want to race a good marathon, you need to run high-mileage consistently. Get your volume up to a high but sustainable level and keep it there.

Perhaps I’ll get around to completing A High-Mileage Manifesto one day. For now, here’s the overview to a proposal I wrote for the book.

In 1945 Arthur Lydiard set out on a five-mile run that changed his life—and the sport of running—forever. The young track racer struggled to keep up with a much older man on that relatively short jaunt and came home humbled, realizing he was not nearly as fit as he’d thought he was. Sensing that the secret to running faster in races was to run farther in training, Lydiard gradually built his endurance to the point where he was able to easily run well over 100 miles every week, which was unheard of in those days. In 1953, Lydiard, now thirty-six years old, won the New Zealand Marathon Championship. Afterward he was inundated by requests for coaching from other runners.

At the 1960 Olympics in Rome, three athletes coached by Lydiard won medals (two of them gold). Suddenly the whole world was interested in Lydiard’s high-mileage training approach. Within a decade this approach had been adopted by virtually every elite runner on earth and was responsible for a drastic improvement in world records at all race distances between 800 meters and the marathon. Today the essence of Lydiard’s training system is still practiced almost universally by professional runners and by most collegiate runners and serious high school runners.

Curiously, however, the vast majority of runners who take up the sport as adults do not run high mileage and are not even aware that this training approach is regarded by every true expert as the necessary path to the full realization of any runner’s innate potential. Of course, the average recreational road racer with a full-time job and a family cannot be expected to run more than 100 miles per week as the professionals do. But it is bizarre that such runners are not even encouraged to run as much as they reasonably can. No other sport is bifurcated in this way, where competitive young athletes and recreational adult athletes are not even taught the same methods to improve.

The split occurred when the sport of running exploded in popularity in the 1990s and it has widened steadily since then. The rapid minting of new adult runners has created opportunities for new coaches to guide and train them. Almost without exception, the opportunists who specialize in mentoring adult recreational runners have little or no background in serious competitive running and were never indoctrinated into Lydiard’s high-mileage training approach. Knowing no better, these pseudo-experts base their own training systems not on high mileage but instead on “new” methods such as high-intensity intervals and technique fixing, which are not new at all but in fact were tried by past generations of elite runners and discarded as inferior.

This madness has to stop. Every runner deserves to know the best way to train. While high-mileage running may not be for everyone, the method that Lydiard perfected sixty years ago yields better results than any alternative even when scaled to fit the lifestyle of the average recreationally competitive adult runner. It’s a crime that this truth, known to all of the sport’s true experts, has been hidden from the masses by lesser authorities. A High-Mileage Manifesto is an overdue corrective that rediscovers the lost secret to running better and motivates runners who are not already enjoying its fruits to give it a try in the way that works best for them.

Written by Matt Fitzgerald, whose previous books include the bestselling Racing Weight and the award-winning Iron War, A High-Mileage Manifesto does not badger busy runners to run more than they really want to. Instead it makes Arthur Lydiard and his method the heroes of a story of triumph against long odds and of lasting survival in the face of wrongheaded challenges. In this way the book gently persuades readers to make their own choice to embrace high-mileage running, which truly can be tailored to work for any runner, as the meaning of “high mileage” is relative.

Like Fitzgerald’s past books, A High-Mileage Manifesto is intended above all to provide a captivating and satisfying reading experience for all runners who enjoy running enough to purchase a book on the subject. Readers will enjoy the author’s rich portrayal of Arthur Lydiard, history’s most iconic running coach, about whom far too little is known by most runners today. They will also gain a new perspective on the history of the sport as Fitzgerald traces the evolution of training methods from the nineteenth century to the Lydiard revolution to today. And they will have their minds blown by Fitzgerald’s limpid explanations of fascinating new science proving the superiority of high-mileage running in unexpected ways that almost no one yet knows about.

The book is organized as a linked set of narrative essays arranged in a loosely chronological order. Chapter 1 lays out the problem to be solved. The next several chapters take the reader on a journey of entertaining persuasion that follows the story of Lydiard’s great idea from its unlikely conception, through its astonishing world takeover and subsequent setbacks, to its ultimate vindication. The concluding chapter tells runners of all experience and ability levels everything they need to know to benefit from high-mileage running. By the time they get there readers will be keyed up beyond all expectations to do just that.

James Spragg is a young South African exercise physiologist who has carved out an interesting niche for his research. It is based on the idea that the fastest athlete on fresh legs is not necessarily the fastest athlete on fatigued legs, which is an important distinction, as in most endurance races, it is better to be the guy or gal who is fastest on fatigued legs. Yet conventional fitness testing protocols ignore this reality, which is a problem, because it has the potential to skew athletes’ training too far in the direction of improving fresh-legged performance.

In one of his early studies, Spragg teamed up with several other researchers, including Iñigo Mujika, whose name you might recognize from his work related to the 80/20 intensity balance, to compare power profiles in nine members of a U23 cycling team and five professional cyclists. Interestingly, they found that the U23 riders were able to generate as much power as the pros on fresh legs. Had this experiment been limited to non-fatigued performance testing, we would have been left to wonder why the U23 cyclists were not also on professional teams. But what Spragg and his collaborators also found was that, in U23 cyclists, achievable power outputs began to decline after 1,500 to 2,000 kilojoules (about 3,600 to 4,800 calories) of prior work was completed, whereas in professional cyclists, performance fell off only after 3,000 kJ of pedaling.

What’s more, a later study by Dutch and South African researchers found that, among top-tier professional cyclists, those able to do the most work before their power output capacity dropped off performed best in races. So, it appears that the ability to ride fast on tired legs is a key factor separating the best from the rest, both between and within echelons of cycling.

Spragg’s recent study is also his most ambitious to date. It involved collecting power data from every training ride and race completed by 30 U23 professional cyclists over three years. The aim was to determine how individual cyclists’ fresh and fatigued power profiles changed over the course of a competitive season and how these changes related to their training. The main findings were as follows:

Fresh power profiles remained relatively stable throughout the season.
Fatigued power profiles changed over the course of the season.
The difference between fresh and fatigued power profiles also varied as the season unfolded, indicating that the two phenomena are independent.
More time spent at low intensity in training predicted better 2-minute power on both fresh and fatigued legs.
A shift away from moderate intensity toward high intensity was associated with a stronger fatigued power profile (i.e., a smaller delta between fresh and fatigued power)

An important implication of these findings is that, depending on the type of event an athlete is training for, performing fitness testing in a fresh state may be of limited value. If you specialize in the 400m freestyle event or the 1500m track event, then perhaps testing in a fresh state has greater relevance. But if you’re training for a marathon or an Ironman 70.3, I would imagine that fatigued fitness testing would tell you more. In a narrative review published in October 2021, Spragg, Mujika, and three other colleagues provide detailed recommendations for incorporating fitness testing into training for road cycling events, one of which is to “avoid single effort prediction trials, such as functional threshold power.” As a running and triathlon coach, I personally lean toward using regular workouts to assess fitness. For example, tacking a fast finish onto the end of a long run serves as a good measure of fatigued performance capacity in a marathoner while also functioning as a relevant fitness-builder for the marathon.

Another interesting finding from Spragg’s 2022 study is that cyclists who maintained their peak training load through the late season also maintained their fatigue resistance, whereas those who reduced their training load during this period lost fatigue resistance. This finding is consistent with other studies reporting a correlation between training volume and fatigue resistance/endurance. One example is a 2020 study byThorsten Emig of Paris-Saclay University and Jussi Peltonen of the Polar Corporation, who collected and analyzed training and racing data from devices worn by more than 14,000 runners for a combined 1.6 million exercise sessions. For the purposes of this experiment, endurance was defined as the percentage of VO₂max running velocity that a runner could sustain for one hour, and the data showed a strong positive correlation between training volume and endurance thus defined.

I wish all of this science had been available when I wrote 80/20 Running back in 2014. It would have bolstered the argument I made therein about how the typical exercise science study design puts a thumb on the scale in favor of HIIT-focused training when compared against the type of training elite endurance athletes do. It’s less of a problem nowadays, but back then it was common to use fresh-legged VO₂max tests as the basis for such comparisons. But we now know that a VO₂max test performed after extensive prior exercise is likely to yield different results that are more relevant to real-world race performance, and that high-volume, mostly low-intensity yields better results in pre-fatigued fitness tests.

Oh, well. That’s what second editions are for, right? In the meantime, you can check out our cycling plans here – some are built to improve your FTP and can be used in your off season.

On January, 22, 2020, five days after thirty-eight year old Sara Hall set a new American record of 1:07:15 for the half marathon, Women’s Running magazine published an article titled “Sara Hall Shares 7 Keys to Her Longevity of Excellence.” For your convenience, I have copied the article’s section headings, which neatly summarize Hall’s secrets, and pasted them here:

“Immersing herself in the love of running”
“Being relentlessly resilient”
“Embracing imperfection”
“Trusting and adapting in training”
“Keeping the faith”
“Focusing on a full life”
“Turning disappointment into teaching moments”

There’s a lot of wisdom packed in these few phrases, but do they constitute a complete recipe for “longevity of excellence”? Of course not, as I’m sure Hall herself would agree. One additional nugget of advice I would offer to aging endurance athletes is this: Assume nothing. By this I mean that you must not assume you will slow down, or your training capacity will decrease, as you get older. Just keep chugging along as though you are immune to the laws of nature that affect other aging athletes and see what happens.

I first heard this advice many years ago from Dave Scott, the legendary six-time Ironman world champion. When Scott was twenty-eight he told his girlfriend Linda Buchanan that he wanted to be even fitter at forty than he was then. Well, he got his wish. In 1994, three months shy of his forty-first birthday, Scott narrowly missed winning a seventh Ironman title, finishing a close second to thirty-year-old Greg Welch. “I didn’t feel like there were any boundaries,” Scott told me years later. “I was constantly reminded of how old I was, but those comments went in one ear and out the other.”

Psychologists have demonstrated that expectations of all kinds tend to be self-fulfilling. It’s not surprising, then, that athletes like Dave Scott, who perform as well after forty as they did before, tend to share a defiant attitude toward the aging process. Some even talk about aging as an advantage. “The more you age, the more you’re getting stronger,” said twenty-seven-time world record-breaker Haile Gebrselassie at a press conference before the 2010 New York City Marathon, when he was officially thirty-seven years old but probably closer to forty-one. “I still feel like age of twenty.” Alas, Gebrselassie wound up DNF’ing the next day, but three years later he was still winning major races, including the Vienna Half Marathon.

Let’s be clear: Age is more than just a number. It is an inexorable biological process ending in death. Athletes who extend their peak performance years into their forties by virtue of high expectations are not defying the laws of nature. If it were not physically possible to set an American record at thirty-eight, Sara Hall would not have done so. In continuing to improve as they approach middle age, the Sara Halls of the world are merely exploiting a possibility that exists in all of us.

This was shown in a recent study by researchers at Germany’s Martin Luther University. The purpose of the study was to identify differences in how older and younger athletes tolerate and recover from high-intensity interval training. Two groups of twelve well-trained cyclists and triathletes, one with an average age of twenty-four and the other with an average age of forty-seven, completed a series of HIIT sessions. During and after each workout, a variety of physiological measurements were taken in an effort to assess how stressful the interval set was for the individual and how quickly the athlete recovered. For example, the researchers looked at the rate at which lactate was cleared from the bloodstream during recovery intervals. They found no differences between the two groups in any of these measurements, leading them to conclude (in language so bloodlessly scientific it’s almost self-parodying), “[I]t seems that the trainability of the organism is maintained.”

Findings like this one suggest that, for athletes over forty who experience a marked decline in performance, the flesh is willing but the spirit is weak. This was certainly Dave Scott’s take, as he explained in the above-referenced conversation: “I think it comes back to how hungry you are in your workouts and how intense you are in your workouts. I coach regular folks. I have thirty-year-old’s, forty-year-old’s, fifty-year-old’s, sixty-year-old’s. . . The intensity of the workouts drops off as people age. They allow it to.”

I’m no Dave Scott or Haile Gebrselassie or Sara Hall, but I am living proof that mere mortals too can extend their peak performance years into their forties if they let the chatter about age go in one ear and out the other. Having raced my first Ironman at thirty-one, I completed my fastest Ironman at forty-eight. Having raced my first marathon at twenty-eight, I completed my fastest marathon at forty-six. And having raced my first 10K at twelve, I completed my fastest one at forty-nine. I repeat: Assume nothing!

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.

Imagine you are completely sedentary and you have been for some time. Then one day you decide to train for a 10K running event. The specific training method you choose is Yoga—30 minutes a day, six days a week. To assess the effectiveness of this program, you actually do a 10K before you start on it and then repeat the race eight weeks later. On this second occasion, you cover the distance more than five minutes faster than you did the first time.

When you tell a runner friend about your success, she says, “Yoga? That’s a terrible way to train for a 10K!”

“Obviously not,” You retort. “Did you miss the part about me lowering my time by more than five minutes?”

The training methods for running a marathon

As absurd as this hypothetical scenario is (absurd but not unrealistic–a previously sedentary person who did a ton of Yoga would substantially lower his or her 10K time), I see athletes commit the same logical error in slightly less absurd ways all the time. It just doesn’t seem to cross the minds of some athletes that there’s a difference between effective and optimal. I’ll give you three concrete examples of methods that typically yield some improvement for the athletes who adopt them but not as much improvement as they would give from adopting proven best practices.

HIIT-Focused Training

In 2013, fitness writer Christopher Solomon wrote a feature article for Outside on his experience of training for a marathon with the CrossFit Endurance method, which relies heavily on high-intensity interval training. Having run a 3:45 marathon five years before, Solomon set a goal of running 3:20 after 13 weeks of CFE training and wound up completing his target event in 3:39.

“Did CFE deliver?” he wrote. “Yes, mostly.” . . . “Would I use CFE to train for my next race? Yes, mostly.”

When I read this article I felt a powerful urge to contact Solomon and offer to train him for his next marathon with the 80/20 method that I favor. It was obvious to me that Solomon had committed the mistake of conflating effective with optimal method and I was quite certain he could get much better results from adopting the endurance training method that has been proven both in the real world and in controlled scientific studies to yield better results than any alternative: 80/20.

The reason athletes often do improve when they switch from their current training approach (which, for the typical recreational endurance athlete, consists of spending 50 to 60 percent of total training time at low intensity, 40 to 50 percent at moderate intensity, and 0 to 5 percent at high intensity) to a HIIT-focused method is twofold. First, this shift often corrects, at least partially, the common and costly problem of getting stuck in the so-called moderate intensity rut. Second, athletes who are stuck in the moderate-intensity rut typically do little to no training at truly high intensities, which are beneficial and which HIIT-focused training methods require.

But again, just because athletes often improve a bit when they try a HIIT-focused training program doesn’t mean they wouldn’t improve more on an 80/20 program. This was demonstrated in a 2014 study conducted by researchers at Salzburg University, who found that athletes who trained in the moderate-intensity rut for nine weeks saw their performance in a time-to-exhaustion test improve by 6.2 percent, whereas athletes who did HIIT-focused training for an equal period improved by 8.8 percent in the same test, and those who did nine weeks of approximately 80/20 training improved by a whopping 17.4 percent—almost double the amount that the HIIT group did.

Low-Carb Diets

It is my belief, based on my observations, that a majority of endurance athletes who adopt very low-carb diets have a bad experience and soon abandon them. But some report getting good results, and many who do wrongly interpret these results as proof that low-carb diets are best for every endurance athlete, or at least for them individually.

In the typical success case, the athlete who goes low-carb loses a substantial amount of weight and achieves a nominal to modest improvement in performance. These anecdotal reports are backed up by some formal studies, including a 2017 study out of Middle Tennessee State University in which eight middle-aged, recreationally competitive male runners lost an average of 5.5 pounds and lowered their 5K times by an average of 2 percent after three weeks on a low-carb diet.

Why isn’t this proof that low-carb diets are best? Leaving aside the fact that this particular study lacked a control group, a runner who loses 5.5 pounds by any reasonable means should lower his 5K time by substantially more than 2 percent. The fact that these runners did not indicates that some negative effect of the low-carb diet partially counteracted the performance benefit of losing weight. Other research indicates this negative effect is impaired exercise economy.

If a low-carb diet was the only way to lose weight, it might still be the best diet for endurance athletes. But it’s not the only way to lose weight. Athletes can enjoy the advantages of both weight loss and adequate carbohydrate intake simply by reducing their intake of low-quality carbohydrate sources (e.g., refined grains) and other low-quality food types (e.g., foods with added fats) and continuing to eat high-quality carb sources (e.g., starchy vegetables). This high-quality, carbohydrate-centered approach to eating for endurance is what the pros do and is, in fact, the best diet for virtually all endurance athletes.

Meathead-Style Strength Training

Recently I created a custom training plan for a client who had a background in personal training but had recently gotten really into running and wanted me to help him achieve a sub-three-hour marathon. Unsurprisingly, his existing strength-training routine relied heavily on exercises such as bench presses and dumbbell shoulder presses that are counterproductive for runners and was utterly lacking in single-leg exercises, balance work, and exercises targeting small but important stabilizing muscles such as the hip external rotators. When I suggested to my client that he modify his strength workouts to make them better resemble those that elite runners do, he pushed back, saying he had good reason to believe he was benefitting from the workouts he was doing.

Sigh.

Now, I will admit that it’s hard to prove that the strength-training methodology practiced almost universally among elite runners today is optimal and that alternatives such as bodybuilding-style strength-training and CrossFit are suboptimal (it’s very tricky to execute a study that would do the job), but I’m confident these things are true. A runner who replaces bench presses and the like with more functional options will lose excess upper-body muscle mass and thereby lower the energy cost of running at any given pace. And a runner who strengthens important but neglected stabilizing muscles will be rewarded with a boost in running economy and reduced injury risk.

No recreational endurance athlete should feel obligated to do things the most effective way. If you want to do HIIT-focused training because it’s fun or adopt a low-carb diet because it’s trendy or lift weights like a bodybuilder because you like how it makes you like with your shirt off, be my guest. But if you want to realize your full potential as an endurance athlete, understand that there’s a difference between effective and optimal and keep this distinction in mind when making decisions about how to train and eat.

There are lots of running-related techniques and methods that are widely known to be effective but that achieve their effects in different ways than most runners believe or assume. For example, drinking water and consuming carbohydrate during endurance exercise are known to enhance performance and are believed to achieve this effect by limiting dehydration and supplying energy to the muscles, respectively, but in fact drinking water enhances endurance performance by reducing the sensation of thirst and consuming carbohydrate does so by acting directly on the brain in a manner that reduces perceived effort. Actually, I lied: these two measures enhance endurance performance in all of the above ways, water by limiting dehydration and reducing thirst and carbohydrate by supplying energy and reducing perceived effort, but you get my point.

Here are three more interesting examples of techniques and methods that don’t work entirely the way most runners think they do.

3 interesting running techniques

High Intensity

Science has supplied iron-clad proof that high-intensity exercise is an essential ingredient of any program intended to optimize endurance running performance. Although high-intensity work should account for only a small fraction of a runner’s total training time, it is impossible to achieve the same level of competitive performance without it.

Why? Most runners believe or assume that high-intensity exercise complements low-intensity exercise via purely physical mechanisms, such as increasing aerobic capacity and lactate tolerance. And it does. But research suggests that the most important difference between high intensity and low intensity may be psychological.

In a 2017 study, British scientists divided 20 healthy volunteers into two groups. For six weeks, one group engaged in an exercise program consisting entirely of high-intensity interval workouts (HIIT) while the other group did an equal volume of exercise exclusively at low intensity. Testing performed both before and after this six-week intervention revealed that although the two exercise programs resulted in roughly equal changes in aerobic fitness markers, members of the high-intensity group exhibited significantly greater improvement in a time-to-exhaustion test and, separately, in a test of pain tolerance.

The researchers concluded, “The repeated exposure to a high-intensity training stimulus increases muscle pain tolerance, which is independent of the improvements in aerobic fitness induced by endurance training, and may contribute to the increase in high-intensity exercise tolerance following HIIT.”

Depletion Workouts

A depletion workout is a workout undertaken without any carbohydrate intake either before or during. For example, you might run 16 miles first thing in the morning on no breakfast and consuming only water as you go. Most runners who are familiar with this practice believe its intent is to enhance the fat-burning capacity of the muscles.

Again, this is true but not the whole story. Although studies have shown that depletion workouts enhance the fat-burning capacity of the muscles, this effect has not been linked to any performance benefit. But other research has demonstrated that the specific stress imposed by training in a low-glycogen state upregulates certain genes involved in mitochondrial biogenesis, and this adaptation does increase endurance performance. In plan English, depletion workouts add horsepower to the body’s aerobic engine. That’s why high-intensity interval sessions, in which glycogen and glucose supply almost all of working muscles’ energy—even when they are done in a carb-restricted state—work just as well as long endurance sessions as depletion workouts.

Plyometrics

Plyometrics is a form of training that consists of various jumping exercises such as hopping up into a box on one foot. It tests an athlete’s ability to produce power, or rapid application of force, and for this reason it is widely believed that the purpose of doing plyometrics as a runner is to increase stride power.

This is true for sprinters but not so much for long-distance runners. In distance runners, plyometrics training has been shown to enhance stride stiffness and thereby increase running economy. The type of stiffness I am referring to is the type that physicists talk about in relation to springs. The human body functions as a sort of spring during running, and just as a pogo stick with a stiff spring will bounce higher than a pogo stick with a loose spring, a runner with greater leg stiffness is able to capture more of the “free energy” that rebounds from the ground into the foot after impact and use it to propel forward motion.

Certain plyometrics exercises, including the drop jump, which entails stepping off a box and landing on the floor below, increase legs stiffness without increasing leg power. The fact that they, too, enhance running economy shows that, for distance runners, plyometrics really is about enhancing stiffness, not power.

The training methods for running a marathon

HIIT-Focused Training

Low-Carb Diets

Meathead-Style Strength Training

3 interesting running techniques

High Intensity

Depletion Workouts

Plyometrics

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