- Review neuromuscular system adaptations as a result of sedentary behavior.
- Understand how the principle of reversibility, the principle of progressive overload, and the principle of specificity play a role in effecting neurological adaptations.
- Learn basic training considerations and methods that will provide a more efficient and effective training stimulus for your client.
Historically, human beings evolved from a time when our survival depended on our physical and mental ability to function optimally. The greatest tool that evolved in response to the constant and imminent challenges, such as food scarcity and natural predators, was the human brain. Our brains underwent rapid evolutionary changes by increasing in size as well as by developing neuronal complexes that make us unique in the animal kingdom. Size for size, we have the largest cerebral cortex, and in particular, the prefrontal cortex, which is located within our frontal lobes, just adjacent to our foreheads. This amazing tool has enabled us to do great things, such as imagine, conceptualize, communicate, empathize, and problem solve. These skills have resulted in our capacity to not only survive those dangerous environments we came from, but to actually thrive, enabling us to grow into the dominant species on this planet.
Over the course of history, species of animals that became extinct did so due to their inability to adapt with the ever-changing environment. There are many examples of species that became extinct because of this, ranging from the dinosaur, to modern day animals. Lucky for us, our amazing capacity to adapt, improvise, and overcome is an evolutionary gift that was presented to us out of necessity for survival. Professor George Williams (1966) once defined adaptation as being an anatomical, physiological, or behavioral trait that contributes to an individual's ability to survive and reproduce ("fitness") in competition with conspecifics in the environment in which it evolved. Famed anthropologist Roy Rappaport (1971) coined adaption as, “The processes by which organisms or groups of organisms maintain homeostasis in and among themselves in the face of both short-term environmental fluctuations and long-term changes in the composition and structure of their environments."
When combining both of these definitions, one can conclude that adaptation is a process in which we evolve in response to the changing environment to maintain homeostasis and survival fitness, no more and no less.
Adaptation to a Modern Environment
Of particular interest is the manner in which we have changed our environment over the past 150 years or so. In an evolutionary blink of an eye, our evolutionary gift, aka the prefrontal cortex, has enabled us to successfully change our environment from a place where large amounts of physical activity were required to obtain food and avoid predation to our modern environment. This modern environment is without the requirement for physical activity, where we have eradicated our natural predators and created an overabundance of food sources. In short, we have created an environment conducive to sedentary behavior and overconsumption of foods. The question here is, what does this mean from an adaptive perspective? If adaptation is defined as a process to maintain homeostasis and survival fitness, how are we adapting to these environmental changes and what does this mean for the fitness industry?
From an evolutionary perspective, what the body does not need in order to maintain homeostasis and survival fitness, it will discard in an attempt to conserve energy. This is known as Dynamic Energy Budget and applies across all species of animals (Sousa et al, 2010). This holds true for all factors of human function, including the nervous system. Research is showing that neurons and motor units adapt to repetitive stimulation, but also atrophy in response to a lack of stimulation. This is known as Denervation (Brooks, 1970), where neuro-muscular junctions decrease in functionality and Disuse Atrophy, where muscle fibers and neurons decrease in numbers (Payton and Poland, 1983). Is it therefore possible that a client’s inability to perform a certain exercise or movement is in part due to the adaptive process of sedentary behavior that has enabled atrophy of the necessary neural and muscular components required to perform a specific movement? If this is the case, then what would this mean for the manner in which we assess movement ability and how we interpret muscular imbalances in the human body? Also, how would this perspective affect the manner in which we develop exercise programs for our clients?
As our environment increasingly promotes sedentary behavior enabling our population to move less and less with the resulting mal-adaptations, then it is plausible to theorize that traditional exercise programming as we’ve known for so many years, may become extinct if it does not adapt to and evolve with our ever changing environment. Predictably, one can hypothesize that if we, as an industry, do not adapt with these environmental and evolutionary changes that, just like the dinosaur or the mammoth, exercise as we know it, may become extinct or ineffective as well. If we are to approach exercise as a fluid and adaptive process, then we must ensure that the laws of adaptation are considered no matter what hybrid exercise forms develop in the future.
Future exercise programs designed to be adaptable to our changing population will require a strong scientific foundation, while simultaneously being adaptable enough to optimize human ability in varying levels of mal-adaptation to our sedentary environment. One way to ensure this happens is by ensuring that we apply the following 3 principles of exercise adaptation.
The Principle of Reversibility (Detraining)
When you stop exercising, your fitness level declines back to baseline levels.
Once training stops, Howly and Franks (2003) state that fitness levels drop to baseline within 3 months. After 3 months, all fitness benefits have diminished. This happens in the nervous system as well. For example, lack of stimulation of postsynaptic neurons results in a reversal of Long Term Potentiation, which is called Long Term Depression. In Long Term Potentiation, postsynaptic neurons become increasingly more sensitive, thus require less stimulation to fire thus enabling a process of effective learning. In Long Term Depression, exactly the opposite occurs where postsynaptic neurons become increasingly less sensitive thus require more stimulation to fire (Carlson 2004).
From an evolutionary perspective, what does this mean for a sedentary 50-year old person who hasn’t moved dynamically since high school PE? With our ever decreasing need to move in our environment, it is highly likely that the central nervous system’s adaptive response is to increase Long Term Depression and possibly even complete atrophy of neurons and maybe even neuronal pathways. This would mean that today’s average deconditioned adult is at a much greater level of neurological deconditioning than perhaps twenty or thirty years ago. Decades ago, what was once considered a basic movement pattern, such as walking, may now be considered a very complex movement pattern. These now complex patterns may require a greater amount of attention from the trainer before the client attempts any form of movement, or functional training program.
The Principle of Progressive Overload
Once the body adapts to a stimulus, no further adaptations will occur unless a new stimulus is provided (Howly and Franks, 2003).
For example, if a person runs the same distance at the same speed during every workout, the legs, heart, and lungs will adapt over time to be able to handle the speed and distance he is running. Once the muscles, heart, and lungs have adapted, they will not develop further or become any stronger if the person does not change the stimulus. Once a greater stimulus is introduced, further adaptation occurs resulting in faster speeds or longer distances.
The same also applies to the central nervous system. Once neuron connections have adapted to a stimulus, neuron connections will not continue to become stronger unless a larger stimulus is introduced.
However, is it possible to over-stimulate a neuron? And if so, what are the consequences for adaptation and learning? Research in neuroscience is showing that the consequences of over-stimulation may be far from ideal. For example, the principle excitatory neurotransmitter in the CNS is Glutamate, which is the key neurotransmitter involved in learning (Carlson, 2004).
Glutamate is widely known to have neurotoxic properties when released in excessive quantities or when it is not recycled sufficiently. Overstimulation from noise trauma, for example, can cause excitotoxicity in the cochlear neurons resulting in function loss (Pujol and Puel, 1999).
This supports the hypothesis that overstimulation of neurons may cause cell injury or even cell death, just as when an athlete or client trains too hard, or intensely and causes injury in muscle cells.
From an evolutionary standpoint, if we are dealing with an ever growing population of people with decreased adaptative function, then it may very well be possible that even basic exercise guidelines as we know it today may be too much stimulation thus causing unnecessary excitotoxicity within the neurons. When training movement ability to a severely deconditioned client, it may be prudent to begin with an extremely basic series of movements with an extremely light load, or perhaps even no resistance, to avoid excitotoxicity, which in turn will only inhibit Long Term Potentiation and learning.
Once the neurons have adapted to these very basic and light movements, then a slightly larger stimulus can be slowly introduced to allow for further adaptation and consistent development toward optimal movement ability.
The Principle of Specificity
The body adapts specifically and only to the imposed demands and nothing more (Howly and Franks, 2003).
A widely used principle in sports conditioning explains that the more specific a form of training is to the sport, the more transfer will occur into performance of that sport (Beachle and Earle, 2008). The principle of specificity holds true in all other forms of exercise as well.
When training for enhanced movement ability, one could assume that simply training movement will make a person more adaptable in that movement. However, when combining this principle with the two previous principles, the concept of transfer becomes substantially more complex.
For the average deconditioned adult with extremely limited movement ability, training movement before the client is ready may actually cause decreased function (as per the principle of progressive overload). Training for movement ability should therefore involve a much broader spectrum ranging from providing just enough stimulation and then progressively build on the neurological adaptations. This calls for a progressive increase in stimulation through manipulating the training variables, such as load, frequency, time and type of exercise. Gradually introduce greater amounts of complexity in movement to stimulate neurological adaptation, which ultimately will translate into a greater and more specific transfer into functional movement ability.
Our ability to effectively train clients to move more efficiently and effectively will depend greatly on our capacity and willingness to acknowledge that we, as an industry, will need to consistently re-evaluate the methods in which we assess our clients and how we develop training programs.
With this in mind, we can theorize that in the not too distant future, traditional training programs may not be optimally effective when teaching movement to our clients and it may involve critical analysis to ensure the effectiveness of these programs. If we are prepared to do so and are open to the challenges ahead, then we could begin to see effective training forms that are still deeply rooted in the science of traditional training, but are capable of adapting with the ever changing environment and population.
- Beachle R, Earle W.E, (2008), Essentials of Strength Training and Conditioning. 3rd edition, National Strength and Conditioning.
- Brooks JE (1970). Disuse Atrophy of Muscle: Intracellular Electromyography. Arch Neurol. 22(1):27-30. Doi:10.1001/archneur.1970.00480190031005
- Carlson NR, 2004, Physiology of Behavior, 8th edition, pgs 123, 428, 429, Allyn and Bacon, 75 Arlington Street, Boston MA 02116
- Howley T, Franks B.D (2003), Health Fitness Instructor’s Handbook, 4th edition, Human Kinetics
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- Williams G C. 1966. Adaptation and Natural Selection: A Critique of Some Current Evolutionary Thought. Princeton (NJ): Princeton University Press.