Depletion Workouts

One hundred years ago, Scandinavian athletes dominated elite distance running. They trained rather differently from today’s elite runners. Hannes Kolehmainen is a good example. His primary fitness activity during the long Finnish winters was cross-country skiing, and even in the summer he did more walking than running. He was, however, among the first elite runners to adopt the then-innovative method of interval training, and that’s a big reason he was arguably the best runner in the world in the late 1910’s.

Fast-forward to 50 years ago. By then, the Lydiard revolution had occurred, and most of the top runners around the world were running 100-plus miles per week, mostly at low intensity. If this formula sounds eerily similar to how today’s top runners train, that’s because it is. Although some innovations have occurred within the past half-century (among them vastly improved strength-training techniques and depletion workouts), the pace of evolution in best practices in endurance training has slowed markedly since Kolehmainen’s day.

This was only to be expected. The human body is the human body. It’s not changing (much), and for this reason endurance training methods can’t just keep getting better and better ad infinitum. But this doesn’t mean they can’t get a little better than they are today. So, what might be different in 2068-9?

Let me begin to answer this question by stating what won’t be different. A high-volume, mostly low-intensity approach will still rule, because it simply cannot be improved upon. The only real alternatives—training less and doing everything fast—have been tried and they don’t work as well.

When making any kind of prediction about the future, the tendency is to assume that science and technology will be the main drivers of change. This could well be the case with respect to endurance training. For example, imagine a technology that dramatically accelerates recovery from training stress and thereby increases overall training tolerance (so that athletes can train even more). Earlier this year I tested a product that is supposed to do exactly this by sending energy impulses into the body. Does it work? Probably not. But it’s entirely possible that something along these lines that doeswork will come along.

As a coach, I’m especially hopeful that advances in science and technology will enable both coaches and athletes make better decisions about how to individualize, plan, and adjust training. Some experts anticipate improved genetic testing to revolutionize training program individualization, but I’m not among them. Genes  tell us surprisingly little about what works best for an individual athlete. A much better picture is provided by starting an athlete off with a program that is based on what works best for athletes generally and then customizing and adjusting it based on ongoing measurements of how the athlete is doing. Already it’s possible to do this quite effectively by simply paying attention to performance in key workouts and how the athlete is feeling. But there’s certainly room for improvement.

For example, through proteomics, coaches and athletes might be able to determine when an athlete is heading for a setback and take measures to avoid it. More immediately, products like PWR Lab are using a similar approach (ongoing collection of vast amounts of relevant data) to predict when injuries are likely occur so that these can be minimized.

On the other hand, it’s entirely possible that the most impactful innovation in endurance training methods will be low-tech, albeit informed by science. These types of advances tend to come out of left field. In 1968, nobody imagined that intentionally depriving the body of carbohydrates before and during select workouts would be a best practice. Who’s to say that sleep-deprivation training (doing select workouts after skipping a night of sleep) won’t be a thing in 1968, having been found to upregulate certain genes related to mental fatigue resistance? Or perhaps endurance athletes will sometimes perform heavy deadlifts in place of active or passive recoveries between high-intensity intervals. And don’t rule out the possibility that elite runners will do some or all of their runs wearing weight vests of gradually decreasing weight over the course of a training cycle.

Unlikely, I know. If I had to wager on the endurance training innovation that is most likely to gain traction at the elite level within the next 50 years, I would put my money on some form of brain training. Specific contenders including zapping the brain with electromagnetic energy before hard workouts, performing mental exercises during certain workouts, and doing similar exercises at rest, between workouts.

May we all live long enough to find out!

There is a strong case to be made for making sure you consume plenty of carbohydrate before endurance training, and also during longer workouts. You will feel better and perform better, especially in harder sessions and in sessions that are begun in a prefatigued state during heavy training periods.

But there is also a strong case to be made for withholding carbohydrate before and during endurance training. These is mounting evidence that exercising with low levels of glycogen in the muscles—which is what happens when carb restriction and prolonged exertion are combined—triggers specific physiological adaptations that enhance subsequent performance.

So, then, what should endurance athletes do: consume carbs before and during workouts or withhold them? Why not both? More and more elite-level coaches and athletes and sports scientists are thinking along these lines. But the devil is in the details. Precisely how should athletes balance high-carb and low-carb training? A new scientific paper by researchers at Liverpool John Moores University takes us a step closer to answering this question. Titled “Fuel for the Work Required: A Theoretical Framework for Carbohydrate Periodization and the Glycogen Threshold Hypothesis,” the paper was published on the online journal Sports Medicine in February and you can access the full text for free here.

In it, the authors propose that there exists a certain critical range of muscle glycogen concentration—specifically, 100–300 mmol/kg dw—that enables athletes to have it both ways in the specific sense that it is low enough to stimulate the above-mentioned physiological adaptations yet high also enough not to impair performance. By manipulating their carb intake before and during workouts in such a way that muscle glycogen levels end up in this range, athletes can gain the maximum benefit from every session. This requires that they consume plenty of carbs before and during their most challenging workouts and go low-carb before and no-carb during the lightest ones.

This approach differs from other “train low” protocols in a couple of respects. First, there is no distinction between fueled workouts and depletion workouts. The fueling objective for all workouts is the same: to provide the muscles with just enough carbohydrate to get the job done. Second, workouts themselves are not manipulated for the sake of achieving some particular metabolic objective. Rather, athletes who follow this approach simply train the same way they’ve always trained and tailor their fueling to the workouts.

The authors of the paper offer a hypothetical example of how their proposed “fuel for the work required” approach might work in progress. It consists of four days of training and fueling in the life of a professional cyclist, summarized in the table below.

man eating carbohydrates during workout

It bears mentioning that fuel for the work required will look quite different when applied to a typical low-volume recreational endurance athlete. For this person, nearly every day would feature low to moderate carbohydrate intake, with only one or two key sessions per week requiring high carb intake before and during.

Whether rigorous application of this approach yields superior results in terms of fitness and performance for either elite or everyday athletes remains to be seen. The authors of the study cite the need for future research to rigorously quantify the “glycogen cost” of different workouts, so that the amount of carbohydrate required can be accurately calculated, and to determine how much inter-individual variation there is in the glycogen levels that elicit the desired benefits.

For my part, I’m not 100 percent convinced that athletes need to reach this glycogen level in every single workout to maximize these benefits. It won’t surprise me if it is eventually discovered that interspersing a few low-glycogen sessions into an otherwise high-glycogen regimen does the job. On the other hand, some of the research on low-glycogen training has shown beneficial effects on body composition, so it’s possible that the fuel for the work required approach could benefit athletes mainly by reducing body fat (as low-carb diets do) without compromising fitness and performance (as low-carb diets also do).

Stay tuned.

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 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.

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