Running Training Adaptation


Written by Jason Karp creator of the REVO₂LUTION RUNNING™ certification program

“adaptation occurs when an organism is exposed to a stimulus to the quality or intensity of which it is not adapted.”

If you spend time talking to evolutionary biologists, they’ll tell you that an organism’s structure evolves to cope with the stresses to which it is subjected. This idea has led to the theory of “symmorphosis,” that an organism’s structural design is regulated by its functional demand., 

As a preeminent anatomist, Ewald Weibel wrote, “…the quantity of structure incorporated into an animal’s functional system is matched to what is needed: enough but not too much.” While symmorphosis is a long process that occurs over millions of years of evolution, structural changes also occur in the short term in response to exercise: bones increase their density, muscle fibers increase their metabolic machinery, and cardiac muscle enlarges. If the quantity of structure incorporated into the runner’s system is matched to what is needed, it’s logical to assume that if you increase the need, you’ll ultimately increase the amount of change that takes place to match the increased need. That’s exactly what happens. 

General Adaptation Syndrome

What happens if you give a mouse a toxic dose of a drug? That was the question posed by Hungarian endocrinologist Dr. Hans Selye in 1950, who discovered that laboratory animals were exposed to various stressors, like drugs, cold, or surgery, and individuals with various chronic illnesses, like tuberculosis and cancer, display a common set of symptoms and pattern of responses.

From his observation of the stress response pattern, Selye developed the General Adaptation Syndrome, which represents the chronologic development of the response to stressors when their actions are prolonged. The response is characterized by three phases: (1) alarm, during which the organism recognizes the threat and begins to react to it; (2) resistance, during which the organism tries to cope with the threat; and (3) recovery or exhaustion, during which the organism has either eliminated or successfully overcome the effect of the stressor, or has failed to overcome the threat, depleting the organism’s physiological resources., Exhaustion, in contrast to recovery, occurs with chronic exposure to a particular stressor that results in lost adaptation.

In Selye’s words: The keynote of this unification was the tenet that all living organisms can respond to stress as such and that in this respect the basic reaction pattern is always the same, irrespective of the agent used to produce stress. We called this response the general adaptation syndrome and its derailment of the diseases of adaptation.

Selye further divided the alarm phase into two stages: shock, which represents the organism’s initial, sudden response to an exposed stimulus, and counter-shock, during which the physiological changes of shock are reversed, and the body’s adaptive mechanisms outweigh the destructive ones. 

At first glance, it would appear that Selye’s research on rodents is far removed from the world of a marathon runner trying to qualify for the Boston Marathon, or a high school runner trying to run a sub-five-minute mile. It is true that Selye’s original research on rodents subjected to involuntary toxic stressors has limitations when applied to the voluntary physical workouts of runners. However, for the first time in the history of science, Selye was able to elucidate the process of adaptation. That’s big-time Science with a capital S. For example, Selye discovered that giving a rodent a small dose (one-quarter) of an alarming/toxic stressor (e.g., drugs, cold, exercise) prior to a full, alarming dose of the same stressor protected the rodent from the alarming/toxic dose. Applied to a runner’s training, introducing a small dose of a specific type of workout is beneficial for adaptation before introducing a larger dose. Selye also discovered that an organism appears to possess a finite amount of “adaptation energy,” with adaptation to a specific stimulus decreasing resistance to other stimuli. As Selye described, “…anything to which adaptation is possible eventually results in exhaustion, that is, the loss of power to resist.”

Using different types of workouts (e.g., aerobic, anaerobic, intervals, strength, power, etc.), training introduces a variety of unique stressors. How your body reacts and adapts to those stressors determines the amount of work that you can tolerate, how much you can adapt to other types of workouts at the same time, and, pure talent notwithstanding, how much you can progress. Following training stress, your body adapts and physiologically over(super)compensates, so that when the same stress is encountered again, it doesn’t cause the same degree of physiological disruption. In short, your body adapts to be able to handle the stress. Following the adaptation, you can do more physical work. The aim of the training is to introduce training stimuli in such a fashion that greater and greater levels of adaptation are achieved, while avoiding the exhaustion phase (and, ultimately, until your genetic potential is reached if so desired). A fundamental understanding of stress and adaptation is imperative to fully understand how and when to prescribe different exercises and workouts.

Adaptation to Training

In Selye’s paradigm of the General Adaptation Syndrome, adaptation is characterized by increased resistance to stress through previous exposure to stress. Thus, stress is at the core of adaptation. Like rubbing one stick against another over and over again to cause chemical changes to ignite a fire, running mile after mile—for weeks, for months, for years—also causes (bio)chemical changes. Each mile, each foot strike, is another rub of one stick against another. If you keep rubbing, positive changes occur. And that’s what adaptation to training is really all about—causing changes from the repeated rubbing of one stick against another. But because you will develop resistance to the rubbing with the previous rubbing, you must rub more to continue to cause positive changes.

How much you adapt to that repeated rubbing ultimately depends on how responsive your cells are to signals. Muscle cells are able to detect all kinds of signals: mechanical, metabolic, neural, and hormonal, which are amplified and transmitted via signaling cascades and lead to the events involved in gene expression. This signaling is fast, occurring within minutes of completing a workout. Signaling results in the activation of transcription factors, which are proteins that bind to a specific part of DNA and control the transfer of genetic information from DNA to RNA.

The physiological and biochemical adaptations to training begin with your DNA, with the copying of one of its double-helical strands (a process called replication). The replicated DNA strand, under the direction of transcription factors, is then transcribed into messenger RNA (a process called transcription), and the messenger RNA is then translated into a protein (a process called translation). Finally, the translated protein is transported from the nucleus of the cell where DNA transcription and RNA translation occur to the place where it will function. From a biological perspective, training is all about stimulating appropriate changes in gene expression and protein synthesis.

Running presents small threats to your body’s survival, and, while you’re recovering after your runs, your body makes specific adjustments to assuage the threats. Each workout, especially if it’s new, causes a specific signal and activation of transcription factors that get busy making messenger RNAs. Big changes occur as a result of repeated runs and repeated threats, which lead to a concerted accumulation of messenger RNAs that are translated into a host of structural and functional proteins that make you fitter and faster. For example, repeatedly running for long periods of time (two hours or more) presents a threat to the muscles’ survival by depleting their storage of carbohydrates (glycogen), which is their preferred fuel. (Long endurance performance is closely linked to the amount of stored glycogen, with muscle glycogen depletion becoming the decisive factor limiting prolonged exercise.) When the muscle fibers run out of fuel, they say, “Hey, this person is running for so long that I don’t have any more fuel. I won’t be able to survive. If this activity is going to be a regular habit, I need to make more fuel.” When you consume carbohydrates following your long run, your body responds to the empty tank by synthesizing and storing more glycogen than usual in the skeletal muscles, which improves your endurance. Empty a full glass, and you get a refilled larger glass in its place. Imagine if your car adapted like that. Imagine if your car sensed when the car’s fuel tank gets very low from driving a long time and, during “recovery,” when your car is sitting on your driveway, it builds a larger gas tank so that next time you drive, you would have to drive for long to run out of gas. Pretty elegant.

Another example of your body’s response to a threat is repeatedly running at fast speeds that cause acidosis, which presents a threat to your muscles’ survival by creating an environment that inhibits enzyme function, disrupts glycolysis, decreases muscle force production, and causes fatigue. When you cause acidosis, the muscle says, “Hey, Jason is running so fast that I’m becoming acidic. I won’t be able to survive. If this activity is going to be a regular habit, I need to create a better buffer to defend the acidosis and maintain my acid-base balance.” So guess what happens? You respond to the repeated acidosis by increasing the size of your muscles’ pool of bicarbonate ions, thus increasing your capacity to do more anaerobic work. 

When you begin a training program, you will experience many signaling responses and subsequent adaptations. However, continued training at the same level decreases the exercise-specific signaling responses involved in the adaptations to training. In other words, if the training stays the same for a while, you can expect your fitness and race performances to stay the same. For example, if you run 15 miles when you’re used to running only 12, you will send a strong signal to make specific adaptations (increased mitochondria and muscle glycogen, etc.). If you continue to run 15 miles every Sunday for months, you’ll continue to send signals to make adaptations until those adaptations are fully realized. After you have run 15 miles so many times that you have become habituated to it, a 15-mile run will no longer be enough of a stimulus to initiate further adaptations, and you may see a plateau in your race times. If you want to force more adaptations, you must run longer than 15 miles (or run those 15 miles faster). As Selye said in reference to his General Adaptation Syndrome, adaptation occurs “when an organism is exposed to a stimulus to the quality or intensity of which it is not adapted.” Thus, not only is training systematic, it must also be progressive. However, you need to balance the training stimulus with adequate recovery because, based on the General Adaptation Syndrome, chronic exposure to a particular stressor may lead to exhaustion, during which adaptation is lost. To become a faster runner, you need to gradually and systematically increase the amount of stress (with adequate recovery) so that you increase the signaling response. Read that sentence again. We will return to this concept many times throughout this book.

As a runner, you may be a little addicted. Runners like to run. A lot. But runners don’t keep adapting to running once the amount of running becomes enough to stop adapting. Unfortunately, your ability to adapt to a training stimulus doesn’t keep occurring indefinitely. There will come a point, which is specific to each runner, when more training, at best, does not lead to better results and, at worst, causes injury. From an adaptation standpoint, the main difference between Olympic athletes and all other runners is that Olympic athletes continue to make physiological adaptations with more and more training, upwards of 100 miles (160 kilometers) per week, and do so while not getting injured. Most runners stop adapting far short of 100 miles per week, and many (most) would get injured with that amount of training.  

If you’re just beginning a training program, either as a beginner runner or after an extended hiatus, any time off during training is detrimental, as you are in the early stages of adapting to the training. If you have been training for years, a week off of training won’t hurt since your body has already created the structural and functional proteins and integrated them into your physiology and biochemistry to become a part of who you are. The longer the time off, the more of these adaptations you’ll lose, but the longer you have been training, the greater the residual effects. Although there is plenty of truth to the adage “use it or lose it,” many adaptations last for a while with reduced training, even up to 15 weeks. It takes a lot more work to get fit than it does to stay fit. 

Specificity of Training

Functional changes take place only in the organs, cells, and intracellular structures that are stressed during physical activity. It seems obvious that if you want bigger biceps, doing squats won’t help. Muscles adapt to the specific demands placed on them. 

But the physical activity you train is not just specific to your muscles; it’s also specific to your brain. Although cycling for hours every day in the countryside can make more mitochondria in your muscles, you need to run to become a better runner, in large part because of the movement pattern of running (and thus the brain’s motor unit recruitment and application of muscle force) is different from cycling. For example, runners use their hip flexors and quadriceps muscles at long lengths due to their upright posture at the hip joint, while cyclists use their hip flexors and quadriceps muscles at short lengths due to their pronounced flexed posture at the hip. The chronic use of these muscles at different lengths by these athletes results in different relationships between muscle length and the forces they can produce at those lengths. The brain needs to “learn” to communicate with the muscles to perform the specific task of running and the muscles need to “learn” to produce force at specific joint angles. Therefore, you need to train the entire movement pattern (the physics) of running in addition to the physiology and biochemistry of running. 

Specificity of training also applies to running on different surfaces, like track, road, grass, and trail. A cross-country runner needs to train on cross-country courses that include grass and dirt. It’s not a good idea for cross-country runners to do workouts on the track while they are in cross-country season. A half-marathon or marathon runner needs to train on the road, especially long workouts, to get the muscles used to the muscle fiber damage they will experience in the race. Good runners will run well regardless of the terrain, but doing all of your workouts on a track to prepare for cross country or on trails to prepare for a road marathon is like a tennis player always practicing on a hard court and then playing a tournament on a clay court. The way a tennis player’s feet move and the way the ball bounces on a clay court is different from on a hard court, just like running on a track is different from running on grass fields and dirt trails or on the road. You need to train on the surface on which you plan to race.  

The specificity of the training principle dictates that, if you want to get faster for a specific race distance, like a mile or a half-marathon, you should train at that specific race pace as much as possible. After all, that would be the pace to train the physics (application of force, angular velocities of body segments, etc.), the physiology, and the biochemistry of the race. However, while training movement certainly needs to be specific to the racing environment, perhaps the great paradox of distance running is that the specificity of training principle does not hold when it comes to training intensity, as the majority of training is performed at a much slower than race pace. Indeed, there is a strong relationship between the time spent training at low intensities and race performances, despite the training speed being much slower than the race pace. Curiously, spending 100 percent or even 50 percent of one’s time training at a race pace is not the way to improve performance for a specific race distance. Why not? This is a fascinating question, one of many about training that this book explores. In general, training becomes more specific to the intensity and demands of the race as the date of the race approaches. Basic fitness adaptations should precede more complex training and performance adaptations. In other words, you must first work on basic fitness before training at a race pace. You must first be fit to train specifically.  

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