“If we could give every individual the right amount of nourishment and exercise, not too little and not too much, we would have found the safest way to health.”
As far back as 400 B.C., the beard Hippocrates posited that exercise was key to promoting human health. Since then, our understanding of this relationship has grown and science has proved Hippocrates correct. The evidence showing that physical activity leads to improved health and longevity and decreased risk of disease is overwhelming. We currently find ourselves in a state of increasing prevalence of chronic disease due to humans engaging in too little exercise (and partaking of too much nourishment). This has led to a prescription for physical activity (150 minutes of moderate-intensity or 75 minutes of vigorous-intensity, weekly) (ACSM, 2014) and exercise to be presented as a “medicine” to coerce individuals to exercise (albeit to largely no avail). The term “exercise is medicine” has also been coined to persuade people into exercising. Health and fitness professionals have taken to this phrase and touted exercise as a wonderful, awe-inspiring, and miraculous godsend; warm and fuzzy feelings ensue as do an infinite number of “inspiring” and self-congratulatory hashtags when people do take their “medicine” (it didn’t happen if you don’t post it). However, is exercise really medicine? Does the body actually change in order to promote health and longevity and reduce the risk of disease? Or is this phenomenon something more mundane; something more fortuitous and accidental than miraculous and deliberate? Is the body really looking out for “you” or is it looking out for “itself” and its greater “purpose”? To address this question, one must look far into the past; past the time of Hippocrates, to the origin of our species and beyond, to the nature that governs life.
“Nothing in biology makes sense except in the light of evolution.”
- Theodosius Dobzhansky
From an evolutionary perspective, the only perspective of which to explain human phenomena, exercise is not “medicine”. As Harvard Evolutionary Biology professor Daniel Lieberman (2015) explains in his paper titled “Is Exercise Really Medicine? An Evolutionary Perspective”, natural selection precludes exercise from functioning as an activity intended to improve health and prevent disease. In fact, while the body can respond “favorably” to physical activity, this favorable response is simply a serendipitous side effect and may actually be at odds with our own biological self-interest. And given that our biology has been shaped by ≈3.5 billion years of natural selection, the biological adaptations to physical inactivity possess an evolutionary explanation as well. Moreover, one must ask, if exercise is so good for us, why do we avoid, even loathe, it so much? Looking at the evolutionary history of our species can provide an explanation for the physiological adaptations to physical activity and inactivity as well as the behavioral dispositions humans have toward exercise; why a session at the gym can lose out to an episode of CSI or Keeping up With the Kardashians that has been seen ≥ 7.6 times, another hour (of the already four straight hours) of SportsCenter, or just simply staring at the ceiling and/or your navel while listening to a newly realized, poorly created Pandora station.
This discussion will center around how exercise is not truly “medicine”, based upon Lieberman’s paper titled “Is Exercise Really Medicine? An Evolutionary Perspective”. (The evolutionary aspects of physical inactivity and behavior will be discussed at a later time).
Humans were not selected to be “fit”
It is well established that regular physical activity is a robust means to improve health, reduce the risk of chronic diseases, promote longevity, and most importantly, look good at the beach and up your Tinder game. These adaptations occur in response to the metabolic and mechanical demands imposed on the body, which force the body to become more resilient to better accommodate those demands. However, the “purpose” of these adaptations are not to promote health and longevity and prevent illness (although we may surely enjoy that as a result and live longer and healthier lives). The adaptations to physical activity, both elevated and reduced (inactivity), rather, are simply a means to handle transient, episodic demands placed on the body. Adaptations to exercise are readily reversed upon removal of the demand. Why is this the case? In order to conserve the (once-)precious resource of energy. Humans evolved under high physical demands and food-insecurity, thus a premium was placed on safeguarding calories that were secured within the body. The body only maintains a level of functioning required to meet the exact demand imposed on it in order to avoid the waste of energy. Energy within an organism is divvied up between reproduction, growth, and maintenance; physical activity falls under maintenance. Engaging in physical activity and, moreover, maintaining the subsequent adaptations, increases energy expenditure; maintaining a more physically capable, or “fit”, body requires greater caloric investment. And while it may seem like the response to exercise is adaptive in that it leads to improved “health” and sickness prevention, this response is actually maladaptive from an evolutionary perspective. Supporting acute physical activity and the chronic adaptations directs unnecessary energy away from endeavors and functions that are adaptive; those that favor the single “purpose” for an organism’s existence: reproduction.
“Fields such as genetics, molecular biology, and physiology are necessary to explain the proximate mechanisms (‘‘how’’ questions) that are immediately responsible for biological phenomena, only evolutionary theory and data can explain the ultimate mechanisms (‘‘why’’ questions) that provide deeper explanations of a phenomenon’s true underlying causes.”
- Theodosius Dobzhansky
Human biology, ranging from anatomy and metabolism to psychology and our very behavior, as well as the sex differences that lie within them, can be explained by looking at the evolution of our species (which split from our last common ancestor with the chimpanzee 5 – 8 million years ago) and understanding Darwin's Theory of Natural Selection. If an adaptation has been retained, such as the ability of the body to change in response to exercise, or lack of it, it provided an advantage for species survival. However, the manner of which a species is assured to survive is not by promoting optimal health in a single, mortal member that will that will be deceased in matter of decades, but to propagate its genes into further generations. The very function and nature of our species (as well as all other animals) can be explained by the single driving force of our existence, that being reproductive success. As such, energy allocation in the body favors reproduction over other biological functions. Until recently, humans (and all our prehuman ancestors over the eons) lived in a food-insecure environment and calories were hard to come by, requiring great physical investment in food procurement. Even more disconcerting, In-n-Out would not be invented for millennia; one would think immediately upon the discovery of fire, the next logical step for the advancement of the human species would be to invent the Animal Style 4x4; however, archaeological data suggest this was not the case. With sustenance under constant question, the divvying up of calories was a fine balancing act to amongst competing biological activities. And since natural selection only favors adaptations that increase reproductive success, humans are developed to divert as much energy as possible toward that end and away from functions that do not lead to increasing the number of human babies.
This diversion of energy includes the diversion away from maintenance of high capacity cardiorespiratory, musculoskeletal, and metabolic systems; what we would consider “fitness”. For evidence of this all one has to do is stop exercising. In a matter of weeks, despite having garnered profound enhancements in fitness, the body returns back to baseline levels and all your gains are lost. Bro. From a biological standpoint, the body does not want to be “fit”, it just wants to reproduce; that is all it has been selected (or, metaphorically, “designed”) for. Per Richard Dawkins, we are indeed held hostage by the “selfish gene”.
Exercise does lead to great increases in physical capacity, or fitness, including improved cardiovascular power and endurance, stronger muscles and bones, enhancements in nervous and metabolic function, and the thorough filling out of size “smedium” V-necks. This is the “why” one exercises; to improve some aspect(s) of physical capacity, whether they be for health, fitness, or performance reasons or out of pure hedonistic vanity. However, these improvements are costly; directing energy away from functions that lead to reproduction, and the body will avoid this as much as possible. Thus, life has evolved to require a stimulus to increase its physical capacities; its fitness. This is the very essence of exercise. If one wants to increase aerobic endurance, one must begin endurance training. If one wants to increase muscle mass, one must begin resistance training. And to maintain these enhancements, the stimulus must continue to be applied; you have to keep training. For as soon as the stimulus is removed, the body will revert back to baseline levels in order to prevent excess energy investment into non-reproductive endeavors (although an argument can be made that the thorough filling out size smedium V-necks may qualify as a reproductive endeavor). The body only improves fitness in order to meet the increased demand placed upon it, once the demand is removed, there is no need to maintain those adaptations. If possessing high performing bodily systems were indeed adaptive, then it follows that these changes in response to exercise would not be so swiftly reversed; sadly, this is not reflected in our biology and Monday will be chest day for the rest of your life.
Adaptation to exercise is essentially your body saying “G*******t, we have to deal with this horse***t”
This explains the “use it or lose” principle. After a period of regular training (i.e. weeks, months, years), despite having garnered profound enhancements in fitness as a result of your whey, sweat, and tears, upon cessation, the body loses what it gained and returns back to the untrained state. After all of the miles ran, after all of the weights lifted (How many weights? So many. So many weights, I can’t even), the gains are not retained. Increased VO2max, improved marathon time, 1RM preacher curl PR, and finally rocking that bro tank without not exhaling for several hours at a time; all reversed. One is left again winded walking up a flight of stairs, crawling across the finish line, not being so impressed by your
own elbow flexion strength that you no longer feel compelled to inundate social media with not-so-subtle (or at all) “look how alpha I am/you would like to have my babies” -related hashtags, and, the greatest of all tragedies, back to sleeves.
You should still exercise
So, while the adaptations to exercise do lead to improved health, and lack of it can lead to degenerative disease, this response, again, did not evolve for that reason. Exercise adaptations are not elicited to promote health or prevent illness, but rather as a means to temporarily meet the exact, ephemeral physical demands on the body, while not wasting energy by increasing fitness over what is required; hence the dose-response relationship. Further, not all diseases are prevented with physical activity. And, excessive exercise can lead to negative consequences. This is not to say, one should not exercise or that physical activity should not be used to promote health and longevity and reduce the risk of disease, not by any means. However, exercise is, indeed, not medicine, but a form of a transient physiological insult that elicits changes in the body that provide “medicinal” side effects at the right amounts that are readily sequestered upon cessation of the demand. This may be a distinction without a difference, but its an interesting paradigm challenge and discussion, nonetheless. With this understood, however, it implies that no minimum dose or ideal dose of exercise exists. No optimal prescription or mode exists in order to promote optimal human function (moreover, what is optimal human function?) Our evolutionary history shows us that the response to physical activity does not represent a therapy intended to promote health and prevent sickness; these are just enjoyable side effects. The response to exercise, rather, is a means to adjust physical capacity in the face of physiological stress in order to fulfill the sole “purpose” of our individual and collective existence, propagate our genes. Perhaps then, the only dose of physical activity that can be prescribed with confidence is that of which allows us the ability to propagate our genes.
Data to be collected on the “Thorough Filling Out of Size Smedium V-necks” hypothesis.
Lieberman, D. E. (2015). Is Exercise Really Medicine? An Evolutionary Perspective. Curr Sports Med Rep, 14(4), 313-319. doi:10.1249/JSR.0000000000000168
Pescatello, L., & Medicine, A. C. o. S. (2014). ACSM's guidelines for exercise testing and prescription (9th ed.). Philadelphia, Pennsylvania: Wolters Kluwer/Lippincott Williams & Wilkins Health.