Animal Instincts of the Human Body: A Psychological and Skeletal Muscular Analysis of Adrenaline on the Human Body


Animal Instincts of the Human Body: A Psychological and Skeletal Muscular Analysis of Adrenaline on the Human Body

Jarrod James
Published by the PIT Journal: 



An adrenaline rush can affect everyone, especially college students who seem to always be under some type of physical, mental, or social stress. An adrenaline rush can take the form of anxiousness, nervousness, or a euphoric excitement in anticipation for some long-awaited, or long-dreaded, event. In students, it can be felt minutes before taking a major test, or in excitement watching the end of a close college football game. An adrenaline rush synchronizes the mind and body to take on the stresses of the outside world. To some, it is a welcomed tension; to others it is an agonizing sensation. In its purest effect, it leaves an individual thinking either one of two things, “I’m ready for this,” or “I don’t want to be here anymore.” People who deliberately seek out this feeling are referred to as “adrenaline junkies.” They search for various ways to satisfy their hunger for thrills by participating in extreme activities such as skydiving and freefalling. In athletes, an adrenaline rush is most commonly experienced during competition, such as when a basketball player prepares to take a game-winning free throw.

My adoration of this feeling along with a passion for sports led me to my research topic: I wish to analyze the psychological and skeletal-muscular effects of epinephrine, or adrenaline, on athletic and physically active individuals. Scholars in the exercise and sports science community typically study the responses of the body when affected by external and environmental stimuli to analyze the body’s response. My primary objective is to analyze the effects of adrenaline on the mind and body from a scientific and psychological approach. Below, I will discuss the physical and mental effects of adrenaline, or epinephrine, on the human body. I also report on an original study exploring the mental effects and strength of those who are stimulated with adrenaline.

To understand its effect on the body, one first must understand what adrenaline, or epinephrine, is. Epinephrine is a hormone released by the adrenal medulla located within the adrenal glands, atop the kidneys (Reece, et al. 528). It is released in response to an environmental stimulus, triggered by the sympathetic nervous system. The sympathetic nervous system is designed to prepare the body for situations of stress and emergency (Merriam-Webster). It decreases smooth muscle contractions, such as in the stomach and intestines, and increases the heart rate. Epinephrine causes the blood vessels to dilate, enabling them to carry more oxygen and nutrients. Blood vessels transported throughout the body deliver more nutrients to skeletal muscles, and vessels leading to the brain induce greater brain function, creating higher levels of alertness and awareness (Reece, et al. 528).  Epinephrine also causes vascular constriction in the veins, thereby slowing the return of blood to the heart. This keeps the nutrient-filled blood within target areas, prolonging activity. Exposure to epinephrine for an excessive amount of time, i.e., several weeks of constant stimulation, or feeling “on edge,” without any set period of rest and relaxation, can be detrimental to one’s health. Excessive exposure causes an increase in blood pressure and a suppression of the immune system (528). Epinephrine is a hormone whose short-term effects benefit the body more than its long-term effects.

Literature Review

Epinephrine is commonly released as a response to physical stress. Because of this, exercise increases its concentration in the blood. The more one exercises, the more it is produced in the body. This phenomenon is referred to as the development of the “sports adrenal medulla” (Kjaer 197). Overstimulation of the adrenal medulla causes it to grow in size and produce more epinephrine. Its occurrence is similar to that of a conditioned muscle. Just like a muscle grows as it is constantly used, so do the adrenal glands. Essentially, athletically trained individuals produce more epinephrine than those who are not athletically trained (196). Athletically trained bodies are also not as sensitive to physical stress. This lessens the amount of epinephrine they release in the bloodstream during physical activities. To put this in perspective, if someone athletically trained and someone not physically conditioned were to run a mile, the non-conditioned individual would receive a higher adrenaline rush from the run than the conditioned individual. This is because the conditioned individual’s body would have adapted to performing activities of that intensity, lowering the amount of epinephrine needed to perform the task efficiently. In comparison, a conditioned individual would be able to participate in more high intensity activities than an unconditioned person because their adrenal medulla would provide enough adrenaline to allow their bodies to adapt to high intensity environments.

Research conducted by MA Febbraio suggests high levels of epinephrine in the blood stream increase glycogen utilization and the rate of glycolysis by the skeletal muscles (Febbraio, et al. 466). Glycogen is a storage form of high-energy sugars within the body. They give skeletal muscles the energy they need in order to contract. Epinephrine allows for greater amounts of glycogen to be released by the muscles for use when engaged in strenuous activity. Glycolysis, or the breakdown of these sugars for immediate energy, allow skeletal muscles to use these sugars at a higher rate. During an adrenaline rush, muscles take quick advantage of glycogen storages in order to produce stronger, prolonged contractions. Glycogen not only aids in increasing the amount of force muscles produce, but also extends how long they can maintain their produced force (467).

Research conducted by Mark French suggests epinephrine and other catecholamines, hormones released alongside epinephrine, stimulate muscular membrane excitability and increase contractile force production (French, et al. 94). These hormones aid in regulating the sodium-potassium pump, needed to maintain muscle excitability, or its readiness to perform an action. Greater contractile force results in more muscle fibers being recruited to perform a high intensity activity.

Though epinephrine allows the body to utilize large amounts of energy, it is not a source of energy itself. Instead, it serves as a hormone stimulant that activates dormant sources of energy to be used by muscles. Hormone sensitive lipase, or HSLs, are fats in the body that are used as energy once stimulated by particular hormones. Evidence demonstrated by Sacha J. West et al., showed increased levels of adrenaline in the blood stream during exercise correlated to an increase in HSL use. Once the fats were stimulated, they were broken down in glucose, and used in the glycolysis process mentioned earlier (728).

An experiment conducted by Gudo A. van Zijderveld et al. supports the idea that epinephrine enhances mental performance (167). In his experiment, 45 college males were tested to see how adrenaline affected their mental performance. The subjects were divided into two groups, high-anxiety individuals and low-anxiety individuals. Then they were tested at their baseline hormonal levels for thirty minutes, after being infused with a placebo for a period of twenty minutes, then after being infused with adrenaline for thirty-five minutes. Every seven minutes subjects were given a series of arithmetic tasks to complete. The tasks involved the subjects stating whether or not equations were either true or false within a five second span. For example, they had to decide whether or not 18+5 = 7 within their allotted time. Ten arithmetic tasks were given, each increasing in difficulty per level. Their answer choices were recorded, along with what they were infused with at the time. Results showed that both subject groups had higher task performance scores when infused with adrenaline than when infused with placebo, or at baseline adrenaline levels (161).

Epinephrine has been shown to affect memory retention. In a study conducted on mice and rats by Debra Sternberg, a group of animals were trained to maneuver through a Y-shaped maze lined with a shockpad used for correction. The animals spent three minutes in the maze for three days, with water being their reward for successful completion of the maze. Twenty-four hours after training, one group of animals was injected with saline while the other was injected with epinephrine. Both groups were tested in the maze again (Sternberg et al. 214-215). The group injected with epinephrine showed a higher percentage of correct choices when maneuvering through the maze than the group injected with saline. Results support the idea that epinephrine aided in memory retention in mammals (216).

It is a common misconception that adrenaline reduces the amount of pain that one feels, but this is not accurate. In some cases, adrenaline may even increase the amount of subjective pain one may feel. In an experiment conducted by Sabine Jansen et al., 24 individuals, 12 male and 12 female, were tested to see if adrenaline amplified or reduced the amount of pain they felt (309). The effect of epinephrine was measured within subjects on several subjective and autonomic measures including: subjective pain, skin conductance response, heart rate response due to electrical stimulation, their threshold for heat pain, and their threshold for pressure pain (309). After being injected with epinephrine, subjects underwent various tests while their sensitivity to pain was analyzed. During some tests, subjects would be distracted before the administered pain stimulus was enacted. There were also tests in which subjects were asked to concentrate on their pain. Results collected from the experiment demonstrated that epinephrine caused a slight increase in subjective pain during electrical stimulation and decreased the amount of pain felt from heat. The heart rate response to electrical stimulation and the threshold for pain caused by pressure were unaffected (309). The main idea presented by this experiment was that, while epinephrine did nothing physiologically to reduce or increase pain, it elevated the mind’s concentration away from that pain, or in some cases towards pain (315). Essentially, what originally made people think that adrenaline reduced the pain they felt was not adrenaline blocking any pain sensors, but the fact that their attention was engaged so strongly in other activities that they were distracted from the feeling pain. Increase in mental concentration is an effect of epinephrine. Whether or not an individual focuses on pain or on another task has the ability to affect the amount of pain he or she may feel. Subjects infused with adrenaline reported an increase in pain if their sole focus was on their pain, and would report a decrease in pain if they were distracted while the painful stimulus was administered.

Original Research

In order to see how adrenaline affects the human body, I conducted an original study.  In my study, seven Division-I athletes were given a two-part survey before and after they worked out. Participants took the surveys in their own athletic facility at the same time between 3:30 P.M. and 4:30 P.M. Both the pre and post workout surveys posed the same questions. The first part of the survey asked three questions meant to assess their psychological state through their mood before they were physically stimulated and after. The second part of the survey included four algebraic equations subjects had to complete as quickly as possible. The second part was timed in order to see how long it took the entire group to finish answering the questions. Directions given regarding the first part of the survey were that each person was to answer the first three questions using either the answer choices provided, or to write their own answer if the choices provided did not reflect how they felt. The questions in the first part of the survey were as follows: “At this current moment how do you feel?”; “Is there a time period in your workout in which you feel more energized than you did at the beginning of your workout?”; and, “How do you feel about yourself after a workout?” Answer choices for Question 1 included: A) Excited ; B) Tired ; C) Content ; D) Indifferent. Answer choices for Question 2 included: A) Never ; B) Once in a While ; C) Usually ; D) Always. Answer choices for Question 3 included: A) Proud of Myself ; B) More Self-Confident ; C) Content with Myself ; D) Displeased/Wanting More.

Afterwards, the group began the second part of the experiment at the same time and finished at various times. Questions in the second part included equations such as 32 = _____; and 24 = ______. Their level of difficulty was such that they could all be answered by someone with a high school education within a matter of forty-five seconds or less. The stopwatch was stopped when the last person in the group was finished.


The results of some questions changed significantly in comparison between pre- and post-workout surveys while others remained stagnant. In regards to the first question, majority of subjects went from feeling energized in the pre-workout survey to feeling either tired or content afterwards. In regards to the second question, subjects went from claiming they felt a period in which they were energized during their workout “once in a while” to claiming they felt this feeling all the time. Recorded answers for the third question did not change, a majority of participants felt proud of themselves after they worked out.  These results are displayed in the following graph:

Figure 1. Recorded Answers for Questions 1-3 in Survey 1 (Pre-Workout)

Figure 2. Recorded Answers for Questions 1-3 in Survey 2 (Post-Workout)

The most notable results were shown in the second part of the pre and post-workout surveys. In the pre-workout survey, the group took 27.57s to solve the equations with percentage of correct answers at 92.9%. In the post-workout survey, it took the group 9.83s to answer the same questions, and their correct answer percentage increased to 96.4%.  Results are displayed in the following graph:

Figure 4. Comparison Between Correct Answer Choices Made In Second Part of Pre- and Post-Workout Survey.

A sample survey with the exact questions and answer choices is included at the end of this article.


Both memory retention and mental awareness showed improvement after the workout. Because subjects’ percentage of correct answers increased, it potentially reflected improvement in cognitive skills. Psychological arousal caused by the workout resulted in increased percentages of correct answers in the math section of the survey, showing that mental stimulation, possibly caused by adrenaline, helped increase mental task performance. This supports data found in Zijderveld’s experiment explained earlier in this paper (167).

The estimated decrease in time it took subjects to complete the math section of the survey was anticipated by the rat and mice experiment done by Sternberg. In order to answer the same questions, quicker subjects would have to remember the questions and be able to recall their former answers, despite whether or not those answers were correct. The increased amount of epinephrine in the blood stream would have to affect memory retention and the speed at which information was recalled in some way (Sternberg, et al. 216).


The purpose of this experiment was to analyze the psychological and skeletal muscular effects of epinephrine, or adrenaline, on the human body. Epinephrine proves itself to be a unique short-term stimulant, increasing in magnitude and capacity as one continues to train the mind and body.  Its unique function beneficially serves its recipient in times of emergency, stress, or enjoyment. It takes advantage of quick energy sources within the body and uses them as food to power the muscles and mind. Epinephrine does not mask pain, but increases the mental concentration of an individual, thereby potentially distracting him or her from the sensation of pain. Adrenaline gives a college student the mental capability to recall information learned at the beginning of the semester in order to answer a question on their final exam. It gives an athlete the extra edge to make him or her jump higher, run faster, or compete at a high intensity that much longer. The feeling of invincibility, or being prepared for anything, is what makes an adrenaline rush one of the most unique human feelings.

The research I have done and my original study have also contributed to opening a much broader question: does physical activity play a role in learning development? If adrenaline stimulated through physical activity causes an increase in brain function, then jogging the day before a major exam might complement cramming for it the night before. If this were the case, then the effects of adrenaline would not only be beneficial to athletes, but also to scholars. 



  1. Adrenaline stimulates the body into becoming physically and mentally capable of engaging in stressful activities. Triggered by the sympathetic nervous system in cases of emergency or stress, adrenaline is released from the adrenal glands into the bloodstream.
  2. The physiological processes that occur in the body as a direct effect of adrenaline released into the bloodstream provide energy to the skeletal muscles and stimulate brain function.
  3. Overstimulation of the adrenal glands causes them to grow in physical size and increase the amount of epinephrine they are able to produce and release. This phenomenon is known as the development of the “sports adrenal medulla.”
  4. Adrenaline increases the amount of glucose that can be utilized by the muscles.
  5. Adrenaline activates hormone stimulated lipase, or HSLs. HSLs are intramuscular sources of fat that are broken down into glucose.
  6. Adrenaline accelerates the rate at which HSLs are broken down into glucose, and the rate at which glycolysis turns glucose into a form of energy that is immediately used by the muscles.
  7. Epinephrine and other catecholamines, hormones released alongside epinephrine, stimulate muscular membrane excitability and increase contractile force production
  8. Adrenaline causes mental arousal and improves cognitive function in the brain.
  9. Epinephrine aids in memory retention in mammals (specifically mice and rats).
  10. Adrenaline does not mask pain. It diverts an individual’s concentration from pain to something else, giving him or her the feeling that the felt pain no longer exists.


Example of Workout Survey Given to Participants

Work Out Excitement Survey

Part One

  1. At this current moment how do you feel?
    1. ) Excited         b.) Tired          c.) Content      d.) Indifferent
  2. Is there a time period in your workout in which you feel more energized than you did at the beginning of your workout?
    1. ) Never            b.) Once in a while      c.) Usually       d.) Always
  3. How do you feel about yourself after a workout? Please circle one.
    1. ) Proud of myself        b.) More self-confident                      c.) Content with myself           d.) Displeased/Wanting more

Part Two

Please answer the following question in the quickest manner possible, take little time between thinking and answering.

  1. 9+5 = _____________
  2. 32 = ____________
  3. 24 = ____________
  4.  simplifies to ______________


Works Cited

Febbraio, MA., et al. “Effect of Epinephrine on Muscle Glycogenolysis during Exercise in Trained Men.” Journal of Applied Physiology 84.2 (1998): 465-470. HighWire. Web. 22 January 2012.

French, Duncan N., et al. “Anticipatory Responses of Catecholamines on Muscle Force Production.” Journal of Applied Physiology 102.1 (2007): 94-102. American Physiological Society.Web. 22 January 2012. 

Jensen, Sabine A., Arnoud Arntz, and Sabine Bouts. “Anxiety and Pain: Epinephrine-induced Hyperalgesia and Attentional Influences.” Pain 76 (1998) 309-316. SciVerse. Web. 4 April 2012.

Kjaer, M. “Adrenal Medulla and Exercise Training.” European Journal of Applied Physiology and Occupational Physiology 77.3 (1998): 195 – 99. SpringerLink. Web. 24 January 2012. 

Merriam-Webster. Medline Plus: Trusted Health Information for You. Merriam-Webster, Inc. Web. 2 Feb. 2012.

Reece, Jane B., et al. Biology Concepts and Connections. 7th ed. Boston, Massachusetts: Campbell. Print.

Sternberg, Debra R. “Age-Related Memory Deficits in Rats and Mice: Enhancement with Peripheral Injections of Epinephrine” Behavioral and Neural Biology 44 (1985): 213-220. SciVerse. Web. 1 February 2012.

West, Sacha J., et al. “Effects of Elevated Plasma Adrenaline Levels on Substrate Metabolism, Effort Perception and Muscle Activation During Low-to-Moderate Intensity Exercise.” European Journal of Physiology. 451 (2006): 727-737. Print.

Zijderveld, Gudo A., et al. “Adrenaline and the Relationship Between Neurosomatism, Aerobic Fitness, and Mental Task Performance.” Biological Psychology. 36 (1993): 157-181. SciVerse. Web. 1 February 2012.

About the Author(s)
Jarrod James