CHAPTER 7

The Engine That Runs Us: Building Endurance

You are not training to run an event. What you are training for is to live a long and productive life and maintain health optimally. For that there is no question that whatever is sustainable is the best type of training.

—DR. TIM NOAKES

MYTH: High-intensity, push-the-envelope workouts will make you stronger, and you can forgo low-intensity workouts.

FACT: High-intensity training, in isolation, creates a toxic, acidic environment in your muscles. It inhibits aerobic development, and will ultimately break you down.

MYTH: When you are exercising, sugar is the best fuel to keep you going.

FACT: Fat is a more efficient fuel than sugar; it causes less physiological stress, and produces greater quantities of useful energy.

Now that we’re properly “positioned” for running, it’s time to work on the endurance that will lengthen our distances, improve our times, and restore our health.

A few years ago I got to know a thirty-six-year-old Air Force musician named Adam Porter. Like many other Airmen, he trained intensively but minimally for a short period just prior to the annual Air Force fitness test, hoping to regather enough fitness to get a passing grade. But as he “trained,” he lost the modest gains he’d made to a combination of burnout, overexertion, and boredom. One year, he failed the test outright, then tried again—and failed again. He had four sons to support, yet was at risk of forfeiting his military career.

I spent a day with him discussing running technique, nutrition, and the concept of maximum aerobic fitness. Mainly, I wanted him to start his training gradually (and well ahead of the test), and to elevate his heart rate to no more than 70 percent of its maximum. Sticking to this plan reduced him to a jog not much speedier than a fast walk. But at the slow pace of 12 minutes and 30 seconds per mile, he was able to work on the principles of natural running form: slowing down, maintaining his balance and gait, not overstriding, bounding, or plodding. Just a smooth, fluid stride.

It took seven months, but Adam shaved four minutes off his mile time. He can now run a mile in 8½ minutes at a heart rate of less than 140 beats per minute. His weight went from 215 pounds to 185.

“My goal is to score in the 90s on the fitness test,” Adam told me, “and to break my 10K personal record of 47:11.” By following the endurance methods explained in this chapter, Adam was able to reach his goal. He scored 100 percent on the running portion of the fitness test.

Most all of us can readily do the same thing.

IT ALL STARTED BACK…

In the 1960s, a New Zealand running coach named Arthur Lydiard became a national legend when he guided his team to an unprecedented string of five gold medals, two silver medals, and two bronze medals in the Olympics. Lydiard had developed a revolutionary training regimen that—counterintuitively—was based on slowing down training speeds for medium and long distances. He exhorted his runners to “train, don’t strain” by having them run at a consistent, relaxed, comfortable pace. This technique, and the principles of physiology that Lydiard drew upon, now guides virtually all endurance-building training programs, and it is widely accepted as the surefire means to building a foundation for health and fitness.

EVERYTHING IS CONNECTED

Let’s take a moment to look at the remarkable biology and physiology that make this work.

As we breathe (from the diaphragm, especially), oxygen diffuses from the lungs into the bloodstream, where it attaches to hemoglobin in the blood. The circulatory system (especially where it branches out to the tiniest blood vessels, our 60,000 miles of capillaries) delivers the oxygen-rich hemoglobin to the working muscles to engage in aerobic activity. We’re off and running.

If oxygen is a good thing, you’d think that hyperventilating would help boost oxygen delivery and improve performance. Instead, you feel lightheaded when you hyperventilate, because you are blowing off carbon dioxide, too, and a low level of CO2 in the blood increases the oxygen molecules’ affinity for hemoglobin. Breathing more slowly allows CO2 levels to naturally rise, which expedites offloading of oxygen to the tissues.

We don’t live (and run) by oxygen alone. Fuel is needed, too, and is stored in the liver as liver glycogen, in the muscles as muscle glycogen, and to a lesser degree in the blood, as blood glucose. (Our blood contains only a teaspoon of glucose, and this level must be maintained within a narrow range. Thus the blood offers no effective sugar storage, nor a buffer against fluctuations. Think of releasing a constant flow of water from an impoundment, but with no reservoir for storage.)

We also carry with us an abundant supply of fuel as lipids, mainly in the form of triglycerides, the building blocks of fat. Some of this fat energy is stored in the belly and around our internal organs as visceral fat, or white fat—the unhealthy kind (that is also difficult to shed). By contrast, fat stored in subcutaneous tissue, or brown fat, is metabolically healthy fat. So is muscular fat, which is carried in our intramuscular stores. The latter two fats are more accessible to us for metabolism and as energy sources than belly fat. Brown fat is abundant with mitochondria.

THE MIGHTY MITOCHONDRIA

The magic happens when the oxygen and fuel converge in the billions of mitochondria—the powerful energy factories within the cells that are stationed around and through our muscle fibers. Each cardiac muscle cell contains about five thousand mitochondria. A biceps muscle has about two hundred. These mitochondria transform potential energy into motion by converting the glycogen and glucose into ATP (adenosine triphosphate, the currency of muscle contraction).

At the same time, through a different process, the triglycerides (building blocks of fat) are mobilized into free fatty acids and glycerol. This is helped along by lipoprotein lipase (LPL), a hormone-sensitive enzyme, through aerobic processes called oxidative phosphorylation and beta oxidation. These are then converted (in the mitochondria) to the ATP that the muscles demand. Amino acids from protein enter this cycle, too, but to a lesser degree.

Ultimately, how we metabolize our fuel—the efficiency with which we convert it into movement and expel waste products—determines how far and fast we run.

The multiple substrates and fuel pathways of aerobic metabolism, leading to the Krebs cycle and oxidative phosphorylation, to produce ATP. Glycogen and triglycerides are the main fuels that we draw upon for locomotion, but protein can also be broken down into glucose through a process called gluconeogenesis.

This isn’t the optimal use of proteins, however, as they are needed for other, “higher,” nonlocomotive functions in the maintenance of health.

THE TWO PRIMARY SYSTEMS OF METABOLISM

For a moment, think of the human body as a car, with the lungs as the air intake; the liver and muscle glycogen as small fuel tanks; our body fat as the large fuel tank; the heart as fuel pump; the mitochondria as spark plugs; and our working muscles and fascia as pistons.

Although visceral (belly) fat may form the largest fuel tank, it suffers from an annoying problem: its prodigious reserves of energy are mostly locked up, and aren’t readily accessible for use by our muscles. This is why belly fat, unfortunately, is so difficult to shed.

A more apt comparison is to a hybrid vehicle, because the fuel in our bodies is burned via two converging metabolic pathways—sugar burning and fat burning. These two metabolic systems work together, not unlike the paired-up combo of a gasoline engine and an electric motor. Let’s take a look at how they combine forces to make the human body the most efficient rig on the road:

The sugar-burning “gasoline” system (mix of anaerobic and high-end aerobic)

When you sprint or make an explosive, momentary effort, you are burning glucose, a quickly metabolized, high-octane sugar. The muscles almost instantly convert glucose to ATP and deliver short bursts of high energy. This is comparable to stomping on the gas and using the hybrid car’s gasoline engine exclusively—which can be handy for powering quickly up a steep, short hill to pass a truck.

This capability has been useful to us throughout our evolution (think fight or flight), but only for about one minute at a stretch. There’s simply insufficient lead time to get a sustained dose of oxygen into the muscles for this instantaneous, on-demand form of energy. And this mostly anaerobic system (it occurs in the absence of oxygen) is limited by the toxic accumulation of acidic by-products—the equivalent of excessive, dark exhaust, in the car analogy. Hard sustained exercise uses the high end of the aerobic system and depletes the sugar/gas quickly and is also “exhaust” heavy.

The fat-burning “electric” system (pure aerobic)

To increase endurance and efficiency, on the other hand, we need to transition out of the sugar-burning “gas guzzling” mode, and switch to the more efficient, fat-burning “electric” system. It’s a cherished myth that if you are exercising at your peak efficiency, sugar is the best fuel to keep you going. In fact, fat is a far more useful energy source, because it offers much more ATP per molecule than sugar does. The metabolic by-products (“exhaust”) from burning fat are cleaner, too, resulting in less harmful inflammation. (Ketone bodies are one product of aerobic-fat metabolism, and have been described as a “super-fuel”—a clean source of energy that can be used directly by the brain and muscle.) As long as you’re burning fat, you’ll pass the smog test.

When driving a hybrid car, you often can’t detect the subtle mixing of gas and electricity. Similarly, your exercising body constantly draws upon a changing mix of fat and sugar. But any vigorous effort lasting more than an hour is best performed in “electric”—aerobic, sustainable, comfortable, fat-burning—mode. When running aerobically on fat, we become resistant to breakdown and can run all day on a minimum of added fuel.

A full battery wins the long-distance race.

THE TRAINING ZONES

When training, racing, or simply exerting at any activity, it is helpful to have an idea of the metabolic “training zone” that your body is operating in. These zones, and the thresholds that demarcate them, aren’t precise. But as you dial in awareness of your exertion level, you’ll be better able to gauge your fuel consumption and how long you can endure at a given level of effort.

The Training Zones

In summary, training constantly in the upper zones—above the AeT/VT—can be harmful. We have recently become aware that years of high-intensity training increase the risk of atrial fibrillation, right heart failure, and myocardial fibrosis. Humans, in order to survive, were designed to move efficiently and comfortably over long distances, with occasional bursts of speed. We weren’t designed to run ten hard miles every day at an anaerobic threshold pace.

SO, WHAT DOES THIS MEAN FOR HOW WE EXERCISE?

As you exercise and train, you can learn to sense which zone you are in and which threshold you might be near. When the blood glucose and muscle glycogen level—the gas tank—is depleted, we crash, or “bonk,” as runners say. The body signals the brain (which strives to maintain a constant blood sugar level) to tell the runner to slow down, stop, or take in nourishment immediately.

Many of us run too hard, yet we get away with it by trying to replenish our easily accessed but quickly depleted glycogen gas tanks in the liver and the muscles. For the fatigued or bonked runner, however, topping off the tank with more sugar, followed by high levels of effort, only repeats the cycle of eating, exertion, and exhaustion. By analogy, it’s better to feed a hot fire by throwing on a log (fat) than by constantly feeding it paper or twigs (sugar).

Months and years of aerobic training and proper diet can make you a “better butter burner”—as in fat burner. One common measure of cardiorespiratory fitness (especially endurance) is an individual’s maximum rate of oxygen consumption, or VO2 max, which can be measured during exercise of increasing intensity. What’s interesting is that two people with the same measured VO2 max—two runners with nominally the same level of maximum endurance—can exhibit, in running lab tests, a marked difference in their abilities to burn sugars or to burn fats. “Fat adapted” athletes can run close to their AT while still burning fat while sugar-dependent athletes switch to sugar at low intensities. In endurance training sessions or long events especially, those who have “trained” their enzymes and metabolism to burn long-lasting fat calories will pull away from those whose bodies have become dependent on stored and ingested sugar. I encourage you to visit runfo­ryour­lifeboo­k.com for my discussion about this, “Burn Fat for Health and Performance: Better Butter Burner,” where I share the results of my 2017 test.

POWER CENTERS AND PATHWAYS

To successfully build our endurance engine (and boost overall health), we need to increase the density of the mitochondria and capillaries in our muscles. This is done through consistent, sustained exercise of light to moderate intensity, and efficient delivery of oxygen to the muscles.

Our bodies can burn glucose and glycogen for only a short period. But most of us, even if our body profile appears lean, have a functionally limitless reserve of fat. We can tap into fat metabolism by slowing down and training within the pure aerobic zone, while maintaining a diet full of healthy fats.

The burning of fat greatly boosts the efficiency of our mitochondrial machinery. Accessing fat provides the environment for building more mitochondrial power centers and more capillary pathways, meaning that even more fat can be metabolized for training runs and races—and for the military’s 1.5-mile fitness test.

The physiology and chemistry is complex, but the practical implications for us are straightforward: the more capillaries and mitochondria we have, the more ATP they produce and the stronger and faster the muscles contract without fatiguing. When you create the demand for long-term performance, the body responds by creating the machinery. This is the hybrid’s electric engine: never empty and always recharging, as long as you eat healthy fats and maintain a comfortable pace. In the car analogy, you are morphing from a Charger to a Prius, and ultimately to a Tesla, as your electric engine grows.

The long-term effect of comfortable endurance training: more energy-delivering capillaries and mitochondria expand and perfuse into the muscles.

Running coach Arthur Lydiard was aware of this. His method of training the best middle- and long-distance runners began with months—even years—of aerobic training. His runners launched the foundational part of their training regimen with easy, aerobic runs—mostly in the comfortable, fat-burning aerobic zone. His 800-meter specialists trained by going on twenty-two-mile runs, and they racked up a hundred miles a week. The reason was simple: he wanted his runners to build a massive and resilient aerobic system. As competitive events approached, he turned up the intensity, by gradual and measured increments, until the runners were pushing their maximum capacity.

For most athletes, six weeks of high-intensity training before an event seems to be the maximum tolerated training period before their level of performance peaks and then may even start to decline as the runner begins to overreach and overtrain. (See chapter 11 on recovery to better understand the important role that rest plays in building strength and endurance.) Muscoloskeletal injury is also associated with high-intensity training over extended periods.

I’m not suggesting that you run twenty-two miles at a pop, or a hundred miles a week, but these principles still apply to almost all modern training programs. A carefully gauged progression works to optimize the body’s daily eustress—the optimum dose of physiological stress that builds health and imparts a feeling of fulfillment. At this moderate level of stress, neovascularization and biogenesis occur in the heart, too, whereby areas of the heart grow new blood vessels and the cells remodel, and more mitochondria and capillaries are formed. This results in a richer network for oxygen and nutrient delivery.

In the year 2000, I began to experiment with pure aerobic training speeds, and as I slowed down, the faster I got—at the same level of easy effort. I began by running ten-minute miles at a heart rate of 150. Six months later, I was running six-minute miles at the same heart rate. That fall, I entered the thirty-thousand-runner Marine Corps Marathon, and finished third, without having done any hard running or speed work.

At the finish line, I was surprised by an unusual sensation, compared with previous races: I felt that I could turn around and do it again. It’s common for runners to feel, after training in the aerobic zone for a few weeks, that they have more energy after their workout than when they began. Try it yourself.

In the early 1960s, Lydiard introduced “jogging” to New Zealanders, and eventually to the world. He also developed the first cardiac rehabilitation program that included jogging as part of its therapy. He knew that relaxed movement was the secret to recovery from heart disease, and he encouraged cardiac patients to build up to thirty minutes of jogging a day (at a conversational pace), over a period of several weeks to months. At that time, by contrast, the U.S. medical establishment was focused on resting the body. Since then, we have learned that bed rest, especially, is very damaging to the heart, and we have adopted Lydiard’s principles. The thirty-minute a day jogging goal for cardiac rehab is now the foundation of the Physical Activity Guidelines for Americans.

In my medical practice, too, I encourage my heart disease patients to slowly ramp up to a jogging pace. Following a heart attack, the heart loses some of its contractility and efficiency. But aerobic training boosts the capacity of the body’s muscles by up to 400 percent, which means that the heart needs to work less for any given activity.

Take the case of local runner Mike Foster, a young father of three. At age thirty-eight, Mike was living a healthy, athletic life. He didn’t smoke, drank little alcohol, and ate healthfully, but he did have a family history of heart problems. In January 2014 he played a game of basketball and felt some pain in his chest (which he assumed was from an elbow in the ribs) and shortness of breath (which he thought was from being winded, following a two-week vacation).

Mike had suffered a heart attack. He promptly underwent quintuple bypass surgery. Afterward, he committed himself to rehab, and set his sights on entering the Freedom’s Run 5K in October of the same year—and he completed it. One year later, following twelve more months of low-intensity training, he broke the tape of the Freedom’s Run marathon. His kids were waiting and cheering at the finish line.

By focusing on comfortable training and overall health, Mike no longer has markers of progressive heart disease. He—and increasingly others—have shown that whole body conditioning may be the best form of cardiac rehab.

SLOW AND STEADY WINS THE RACE…

Many believe that high-intensity, push-the-envelope workouts make you stronger and fitter than low-intensity workouts. This may work temporarily, but can create a toxic, acidic environment in the muscles, inhibiting the aerobic development that we seek.

Less acute, but just as damaging in the long term, is falling into the “black hole” of training. This comes from consistently training above your aerobic threshold, and not allowing sufficient time for recovery. Many of us do this, and wonder why our performance declines. It distresses me to see people destroying themselves in brutal, intense daily workouts in the name of athletic excellence (or to “make up for lost time”). We need to slow down in order to speed up, and we need to run with joy. As the minimalist running tribe leader and friend Barefoot Ted says, “Don’t practice pain. Practice pleasure.”

There’s no hurry. We are training for the rest of our healthy lives.

Slow and steady wins the race.

DRILLS

To determine the best, sustainable level of exertion for building the aerobic (“electric”), fat-burning engine, it’s best to have a trainer or master teacher. But a heart rate monitor can work, plus some simple measurements and record keeping. Once you reach a fitness plateau, you shouldn’t even need these.

1. Determine your maximum aerobic heart rate

There are several methods for finding your maximum aerobic heart rate (MAHR)—the sustained rate that will best build your endurance engine. This heart rate (or range, within a few beats per minute) is most easily and safely determined by using the “180 Formula,” developed by Dr. Phil Maffetone in 1982. Despite some differences, other methods for calculating this work fine—most of the time. The Karvonen formula and the Friel method, based on lactate threshold, work well, but deriving MAHR from them is more complicated.

Elite athletes Mark Allen and Mike Pigg, among many others, have successfully used the 180 Formula for building a solid foundation for health and world-class performance, and for extending their race careers. I’m confident that you’ll discover what we have: although your heart rate remains in check over the weeks and months of training, your endurance, your feeling of well-being, and your speed will improve.

The 180 Formula

Subtract your age from 180 (180 – age). This gives you a baseline beats per minute (bpm).

Then modify this number by selecting adjustments that match your health profile:

For example, if you are thirty years old and have not been training consistently, then your MAHR would be:

180 – 30 = 150, then 150 – 5 = 145 bpm

In my case, I am fifty-one years old and work out at least four times per week, and I’ve been healthy, so I add 5 bpm to the raw number of 180 minus my age. I end up with a MAHR of 134 bpm.

Whatever figure results from this calculation, this maximum aerobic heart rate generally falls within the range recommended by exercise physiologists as a safe aerobic training heart rate: 60 to 80 percent of one’s maximum heart rate—the highest rate that your heart should normally reach during extended physical exertion. The 180 Formula is slightly conservative, and therefore especially good if you are new to running, are recovering from an injury, or don’t feel sufficiently fit to take on the high-intensity run.

A choice few who are very accomplished at fat burning can be a bit more liberal—with caution—and work out at a maximum aerobic heart rate of 200 minus their age.

And you may find that getting a test of your VO2 is a very useful tool. By measuring respiratory gases in a physiology lab, it’s possible to determine whether you are running in the aerobic zone. The VO2 max figure that results from this test will give you an idea of your overall aerobic ability. But VO2 levels at less-than-maximum effort may be even more useful as an indicator of whether you are burning fat or sugar. (As glucose metabolism increases, you produce more CO2, which signals that you are leaving the fat-burning aerobic training zone and entering the anaerobic zone.) A local exercise physiologist may be able to test your VO2, or a university sports science department may offer the test for free.

2. Measure your progress—with one simple assignment

Assuming you are committed to improving your overall aerobic fitness, then how do you track your progress? For that matter, how can you be certain that you are improving at all? The feeling that you are becoming healthier and aerobically fit is often subjective, especially for those who haven’t been exercising regularly. But once you know your maximum aerobic heart rate, a simple way to measure progress is to apply what’s called the maximal aerobic function test:

With experience, you should be able to remain in your aerobic training zone simply by sensing your level of effort, without a heart rate monitor. Feel the rhythm of your breathing and your level of exertion, pay attention to your feelings, set mental reference points, and learn the language of your physiology. Develop your own system of biofeedback. One reliable way to do this is to limit yourself to breathing through your nose. If you can maintain a genuine smile, too, you will feel as if you can run forever.

Once your times on the two- to three-mile course are no longer improving—typically after several months, and sometimes years—you have fully built your aerobic endurance engine! You will notice that you are faster than ever before, yet running at a level of exertion that is as easy and comfortable as the day you began.

In some instances, it may be necessary for your heart rate to drift above your MAHR:

It’s probably not helpful to train with a group that runs at a pace that will take you above your own MAHR, at least not every day. On a group run, your heart rate will naturally climb as the pace quickens. When you crest a hill or when the pace settles, focus on relaxing and recovering.