Repeating Great Performances with Muscle Memory

labeled_diagram_human_brainHave you ever wondered how professional tennis players are able to put a serve right on the line time after time? How about how a professional golfer is able to pull off pin-point shots with extreme consistency? Aside from intense focus, these athletes are using motor learning, also known as muscle memory. This is essentially teaching your muscles how to repeat movements or techniques over and over.

Learn the basics of how muscle memory matters.

Article by Kenny Morley

The Physiology Behind Performance-Enhancing Drugs (Basic)

Thomas Hicks

In 668 BC, Charmis won the Olympic 200-yard running race after eating a preparation of dried figs (Yesalis and Bahrke 2002). In 1904, Thomas Hicks ate strychnine, brandy and five eggs to increase his endurance and help him win the Olympic marathon (Jones 2012). Since the beginning of organized competitive sports, professional athletes have experimented with ways to increase their athletic potential.

Today, this process is termed doping, or using performance-enhancing substances to increase athletic ability. The World Anti-Doping Agency (WADA) was created to level the playing field between athletes and assist sport organizers in combatting the problem of doping (World Anti-Doping Agency 2012b). Every year, WADA publishes a list of prohibited substances; testosterone and other anabolic-androgenic steroids (AAS) are at the top of the list (World Anti-Doping Agency 2012b). In 2010, testosterone and AAS were found in 60% of the blood and urine samples that tested positive for containing an illegal substance (World Anti-Doping Agency 2010).

Testosterone is an androgen, a hormone that is normally found in the body.  It controls the development of sexual organs and secondary sex characteristics that occur in puberty.  It is also involved in muscle development. Testosterone, by binding to the androgen receptor, controls expression of the genes responsible for these changes (Deroo and Korach 2006). With doping, athletes take advantage of this natural process and try to find ways to increase the levels of testosterone in their body to enhance their muscle development (Storer et al. 2003).

However, changing the natural balance of testosterone also leads to the development of several medical conditions.  Men using high doses of AAS can have estrogen levels as high as women during a normal menstrual cycle, leading to breast development (Wilson 1988). Women develop facial hair but lose scalp hair.  Both sexes develop higher levels of cholesterol in their blood, leading to blockage of the arteries and heart attacks (Shahidi 2001). In athletes from the former East Germany, these effects have even been transferred on to the athletes’ children who suffer from asthma, allergies and crippled feet or legs (World Anti-Doping Agency 2012a).

While some athletes think abusing testosterone is worth the risk, doping is like playing a game of Russian roulette. Eventually, an athlete is going to lose. Although much is known about hormonal regulation, androgen receptors are expressed in many different types of cells, so many of the long term effects of testosterone abuse are unknown. Also, athletes caught doping can be disqualified, banned from future competitions, or stripped of their medals (International Olympic Committee 2012). What’s the point of being an athlete if you can’t compete?

Learn more technical details about performance-enhancing drugs.

By: Kirstin Roundy, University of Utah
Kirstin Roundy holds a M.S. in Laboratory Medicine and Biomedical Science from the University of Utah. She spent 14 years working as a biomedical researcher studying the gene regulation in B cell development. She enjoys acquiring knowledge and takes random, non-credit classes just so she can learn something new. Her favorite sport is soccer.

References

Bowers, L. D. 2009. The international antidoping system and why it works. Clin Chem. 55:1456–61.

Deroo, B. J. and K. S. Korach. 2006. Estrogen receptors and human disease. J Clin Invest. 116:561-70.

International Olympic Committee. 2012. Anti-Doping Rules. Retrieved from http://www.olympic.org/fight-against-doping/documents-reports-studies-publications

Jones, D. S. 2012. Olympic Medicine. N Engl J Med. 367:289-92

Shahidi, N. T. 2001. A review of the chemistry, biological action, and clinical applications of anabolic-androgenic steroids. Clin Ther.  23:1355-90.

Storer, T. W., L. Magliano, L. Woodhouse, M. L. Lee, C. Dzekov, J. Dzekov, R. Casaburi, S. Bhasin. 2003. Testosterone dose-dependently increases maximal voluntary strength and leg power, but does not affect fatigability or specific tension. J Clin Endocrinol Metab. 88:1478–85.

Wilson, J. D. 1988. Androgen abuse by athletes. Endocr. Rev. 9:181–99.

World Anti-Doping Agency. 2010. Adverse Analytical Findings and Atypical Findings, Reported by Accredited Laboratories. Retrieved from http://www.wada-ama.org/en/Science-Medicine/Anti-Doping-Laboratories/Laboratory-Statistics

World Anti-Doping Agency. 2012a. Sport Physicians Tool Kit. Retrieved from http://www.wada-ama.org/en/Education-Awareness/Tools/For-Sport-Physicians

World Anti-Doping Agency. 2012b. The 2012 Prohibited List. Retrieved from http://www.wada-ama.org/en/Science-Medicine/Prohibited-List

Yesalis, C. E. and M. S. Bahrke. 2002. History of doping in sport. Pages 1-20 Performance-enhancing substances in sport and exercise, 1st edn, Human Kinetics, Champaign, IL, USA.

Fast and Furious: How Muscle Fiber Type Influences Basketball Performance

Muscle-fibers-631x421Professional athletes use a unique combination of speed, agility, strength, and power to stand apart from the rest. This winning combination of traits is largely due to the slow-twitch (ST) and fast-twitch (FT) fibers found in their muscles. ST fibers are important for endurance, as they allow the muscles to contract at a slow rate for a long time. On the other hand, FT fibers contract fast and hard, but only for a short time, and are important for sprinting. The body first turns to the ST fibers for movement, then focuses on the FT fibers in their legs, calves, and buttocks as the athlete increases speed. A combination of balance, lateral movement, T-drill exercises, and core training are important to increase this muscle response time and maximize gains.

Read about basic muscle fiber and performance or learn the technical physiological explanation.

Articles by Josh Silvernagel

95 miles per hour: Physiology of Pitching

Nationals_Rockies_Baseball-00baa-27438Baseball has been America’s pastime since its early beginnings.  Over time, fans have watched the game evolve. In many cases, the game seems to boil down to a battle between pitchers.  Franchises competing for a spot in the World Series seem to know this, and many (such as the San Francisco Giants) have heavily stacked their pitching rosters with notable talent.  So, physiologically speaking, how do pitchers do what they do, pitch after pitch after pitch?  And what parts of their bodies are most prone to injuries?

These are complex questions. The obvious place to begin is with the arm, shoulder and back muscles.  The most vulnerable joint in pitching is the glenohumeral joint, which is commonly known as the ball and socket of the shoulder.  This joint has the greatest range of motion of any joint in the body.  It is directly supported by four rotator cuff muscles that attach with tough, sinuous tendons.  The pectoral muscle group and the lassitimus dorsi are larger muscles, located in the front and back of the shoulder.  They help stabilize the joint and help keep it from over-rotating and causing injury.

These and other muscle groups work to gather and release energy during a pitch, and others counter the whipping motion of throwing the ball, acting to decelerate and prevent the arm from injury.  In addition to the muscles used in the back and shoulder, leg and core body muscles significantly contribute to the power behind the pitch.  It is this symphony of muscles working in tandem that allows pitchers to throw 100 mph pitches.

Read more about the basics of pitching and physiology or learn the technical physiology behind pitching.

Articles by Josh Silvernagel

Hydration and Sport Beverages (Technical)

Athletes have many factors to consider when it comes to improving performance. An element that is commonly overlooked is hydration. Fueling the body involves not only choosing nutritious food options, but also consuming the required fluids and nutrients to remain hydrated. With numerous hydration options available to athletes, it is requisite to examine the existing research and recommendations to promote proper hydration for athletic participation.

The importance of attaining and maintaining an adequate hydration status cannot be overstated. The human body weight is comprised of approximately 60 percent water, and water takes part in a number of chemical reactions within the cells of the body. Water also serves as a medium for allowing nutrients to pass from the blood to the cells, and for metabolic products to transfer from the cell to the blood (Gropper et al. 2008). Water also plays an important role in thermoregulation and maintaining the body’s temperature. In addition to these roles, water is necessary for most other physiological processes (Dunford and Doyle 2012). As physical activity leads to additional physiological stress, hydration is an essential consideration for athletes and individuals participating in physical activity.

Because the body functions best when homeostatic conditions are maintained, the goal in regard to hydration status is euhydration. Euhydration refers to a state in which there is a sufficient volume of water to meet the physiological requirements of the body (Dunford and Doyle 2012). Deviations from the euhydrated condition include hypohydration and hyperhydration. Hyperhydration is a condition in which there is increased body water content, and hypohydration refers to a decreased body water content (Sawka et al. 2001). Both of these conditions can lead to detrimental symptoms, particularly in relation to exercise and sport performance. These conditions will be discussed next.

Hypohydration occurs by the process of decreasing total body water, or dehydration. Dehydration leads to several unfavorable symptoms due to the increase it causes in physiological strain. Measures of physiological change include heart rate, core temperature, and perceived exertion responses. These measures have been demonstrated to be increased during exercise or heat stress in the dehydrated condition (Sawka et al. 2001). Another effect of dehydration, particularly when the level of dehydration is greater than two percent, is a decrease in both cognitive performance and aerobic exercise performance (Cheuvront et al. 2003). The greater the extent of the body water deficit, or the greater the dehydration level, the greater the impairment in aerobic exercise performance and increased physiological strain (Montain et al. 1992, Institute of Medicine 1994). Thus, the importance of avoiding the dehydrated condition is great, particularly in the case of athletes, as dehydration impairs body functions and athletic performance.

Hyperhydration refers to increased body water content, and has sometimes been touted as a method for improving exercise performance. The hyperhydrated state is not accomplished by merely overdrinking, but combines overdrinking with an agent that binds water in the body, such as glycerol or a hypertonic drink. The reason for this is that overdrinking alone prior to exercise will likely lead to increased urine production, and will not achieve a hyperhydrated condition (American College of Sports Medicine et al. 2007). Another concern in this realm is that during exercise, urine production is less and sweat rate is increased, leading to a consequently heightened risk of hyponatremia. Hyponatremia is a condition in which plasma sodium levels are decreased to a level of 130 mmol/L or less, either by increased fluid diluting the plasma, or inadequate sodium (Rehrer 2001). Symptoms of hyponatremia include headache, fatigue, confusion, vomiting, wheezing, and swollen feet or hands (American College of Sports Medicine et al. 2007). In more severe cases, seizures, coma, respiratory arrest, and even death are possible (Zambraski 2005). As has been described, there are a number of potential negative effects of hyperhydration, and research has demonstrated limited benefit to hyperhydrating. Any performance benefits observed may be associated with the delay in dehydration onset, however there are no thermoregulatory advantages of hyperhydrating (American College of Sports Medicine et al. 2007). Thus, it is generally not recommended to aim for hyperhydration, but rather athletes are encouraged to strive for a euhydrated state.

As is demonstrated by the previous descriptions, excessive deviations from a condition of fluid balance in the body can have detrimental effects on health and athletic performance. Thus, a key concept to examine is the source of fluid losses from the body, as well as various means of fluid gains or fluid replacement to the body. The primary routes of fluid losses include respiratory, renal, gastrointestinal, and sweat. Respiratory and gastrointestinal losses tend to be quite low, while urine fluid losses are regulated by the kidneys to aid in maintaining water balance. Fluid losses via sweat vary considerably based on factors such as individual sweat rate, environmental temperature and conditions, intensity and duration of physical activity, clothing, and equipment. Individual sweat rates also vary based upon characteristics such as weight, heat acclimatization, metabolic efficiency, and genetic factors (American College of Sports Medicine et al. 2007).

Due to the increased fluid losses incurred during participation in physical activity, and the importance of maintaining fluid balance, specific recommendations for replacing fluid losses have been set in place by the American College of Sports Medicine. These recommendations include guidelines and goals for hydration before, during, and after exercise. The recommendations are summarized in Table 1. Note that these are general guidelines that should be used as a starting point for developing an individualized hydration plan for each athlete.

Table 1. Fluid Replacement Recommendations.8

Goal

Fluid Recommendation

Other Nutrients

Before Exercise

Start physical activity euhydrated, with normal plasma electrolyte levels 4 hr prior: Slowly drink fluids (5-7 mL/kg)2 hr prior: If do not produce urine, or urine is dark- drink more fluid (3-5 mL/kg) Consuming sodium (either in the beverage or from food) will help increase thirst and assist in fluid retention

During Exercise

Prevent greater than 2% body weight loss, excessive dehydration, and extreme alterations in electrolyte balance Individualized fluid replacement program based on duration, intensity, environmental conditions, opportunities to drink, and individual sweat rate. <60 minutes: Water and perhaps electrolytes should meet needs>60 minutes: 30-60 grams/hour carbohydrate (from food or fluid). Caffeine may help sustain performance

After Exercise

Replenish all fluid and electrolyte losses If recovery time not limited: Normal meals, snacks, and water should sufficeLimited recovery time or excessive dehydration: 1.5 L fluid for each kilogram body weight lost (consume over time rather than large bolus) Sodium from food or beverage to replace losses. Carbohydrates and protein from food or beverage to replenish glycogen stores and promote muscle anabolism

Numerous beverages and sports drinks are promoted as being beneficial or necessary for fluid replacement in relation to athletic participation. The recommendations in Table 1 summarize the fluid and nutrient requirements before, during, and after exercise; however there are many potential routes that can be taken to accomplish an appropriate hydration status. Beverages and products often touted in association with exercise and fluid replacement include water, sports beverages (Gatorade, Powerade, etc.), protein drinks, milk, chocolate milk, and caffeinated beverages. The research relating to each of these will be detailed next.

For exercise in moderate environmental conditions, water should be sufficient for meeting hydration needs for activities lasting less than one or two hours. For activities of greater duration or more extreme environmental conditions, electrolyte (particularly sodium) and carbohydrate replacement are in order (Dunford and Doyle 2012). These needs can be met by a variety of methods, such as foods, gels, or beverages. If a sports beverage is used to help meet these needs, the Institute of Medicine advises that the composition of the beverage should be as follows: 20-30 meq/L sodium, 2-5 meq/L potassium, and about 5-10% carbohydrate (Institute of Medicine 1994). The role of the sodium and potassium is to replace electrolytes lost in sweat. Sodium also plays a role in increasing thirst, which aids in fluid replacement. The primary role of carbohydrate is the provision of energy, and when carbohydrate containing beverages are consumed during exercise, it is recommended that they contain 6-8% carbohydrate (American College of Sports Medicine et al. 2007).

Milk and chocolate milk have been promoted as potentially effective recovery beverages for post-exercise use (Roy 2008). Chocolate milk is the more commonly researched beverage due to the increased flavor desirability, particularly following exercise. Chocolate milk contains carbohydrate in similar amounts to many sports beverages, and also contains the proteins casein and whey. Protein in the recovery period may assist with muscle anabolism, and has been recommended to be consumed following exercise, either in food or beverage form (van Loon 2000). Chocolate milk also assists with hydration and fluid replacement following exercise, and provides the electrolytes sodium and potassium, which can aid in replacing electrolytes lost in sweat (spaccarotella and Andzel 2011). Due to potential intolerance immediately before or during exercise, it appears the composition of chocolate milk is best suited for the post-exercise recovery period.

As mentioned previously, it is recommended that protein be consumed in addition to carbohydrates following exercise. Thus, numerous protein beverages have been promoted as recovery beverages for the post-exercise period. Products such as the Gatorade G Series Pro Protein Recovery Shake, High-protein Boost, Endurox R4 Powder, and several others are high-protein beverage options commonly promoted for post-exercise use (Dunford and Doyle 2012). Each of these products varies in their precise content, but all provide both protein and carbohydrate, which seem to have a synergistic effect when used together in recovery beverages. Potential benefits include rehydration, replenishing glycogen stores, and protein turnover, all of which may be beneficial for subsequent athletic performance (Goh et al. 2012). The exact macronutrient distribution does not seem as influential on the effects of the beverage, provided the beverages compared are isocaloric and contain both carbohydrate and protein (Goh et al. 2012).

Caffeinated beverages have also been used for their stimulatory effects to aid in athletic performance. A common concern associated with caffeine and hydration is the potential diuretic effect of caffeine. A review of the existing research on caffeine and sports performance summarized the research in this area and concluded that caffeine, when taken in appropriate and not excessive amounts, does not impair overall fluid status, and athletes may choose to use caffeine prior or perhaps during exercise for its potentially beneficial performance effects (Burke 2008). In the realm of recovery beverages however, there is some evidence to suggest that caffeine consumption can increase urine output and therefore negatively affect rehydration status (Gonzalez-Alonso et al. 1992).

In sum, hydration is a critical element affecting athletic performance, as well as overall health. Excessive deviations from the euhydrated state, either in the direction of hypohydration or hyperhydration can potentially lead to detrimental effects. Recommendations have been established for hydration before, during, and after exercise, and these should be used as a guide for developing an individualized hydration plan for each athlete. Numerous beverages and products are available for assisting with meeting the athlete’s hydration needs, and several have been reviewed here. Regardless of the products selected for the means of hydration, athletes should make maintaining appropriate hydration levels a priority in order to maximize their health and athletic performance.

By: Jamie Saunders, University of Utah
Jamie Saunders has always been interested in the area of nutrition and wellness. Saunders graduated from Southern Utah University with a Bachelor’s degree in Human Nutrition, and from the University of Utah’s Coordinated Master’s Program in Dietetics, with an emphasis in Sports Dietetics. She is a Registered Dietitian and currently works as the Outpatient Dietitian for the University Health Care’s South Jordan Health Center.

References

American College of Sports Medicine, Sawka M. N., L. M. Burke, E. R. Eichner, R. J. Maughan, S. J. Montain, and N. S. Stachenfeld. 2007. American college of sports medicine position stand: Exercise and fluid replacement. Medicine and Science in Sports and Exercise 39: 377-390.

Burke, L. M. 2008. Caffeine and sports performance. Appl Physiol Nutr Metab 33: 1319-1334.

Cheuvront, S. N., E. M. Haymes, and M. N. Sawka. 2003. Fluid balance and endurance exercise performance. Curr Sports Med Rep 2: 202-208.

Dunford, M. and J. A. Doyle. 2012. Nutrition for Sport and Exercise, 2nd edition. Wadsworth, Belmont, California, USA.

Goh, Q., C. A. Boop, N. D. Luden, A. G. Smith, C. J. Womack, and M. J. Saunders. 2012. Recovery from cycling exercise: Effects of carbohydrate and protein beverages. Nutrients 4: 568-584.

Gonzalez-Alonso, J., C. L. Heaps, and E. F. Coyle. 1992. Rehydration after exercise with common beverages and water. Int J Sports Med 13: 399-406.

Gropper, S. S., J. L. Smith, and J. L. Groff. 2008. Advanced Nutrition and Human Metabolism, 5th Edition. Thompson Wadsworth, Belmont, California, USA.

Institute of Medicine. 1994. Fluid replacement and heat stress.

Institute of Medicine. 1994. Fluid replacement and heat stress.

Montain, S. J. and E. F. Coyle. 1992. Influence of graded dehydration on hyperthermia and cardiovascular drift during exercise. J Appl Physiol 73: 1340-1350.

Rehrer, N. J. 2001. Fluid and electrolyte balance in ultra-endurance sport. Sports Medicine 31: 701-715.

Roy, B. 2008. Milk: The new sports drink? A review. J Int Soc Sports Nutr 5.

Sawka, M. N. and E. F. Coyle. 1999. Influence of body water and blood volume on thermoregulation and exercise performance in the heat. Exercise and Sports Science 27: 167-218.

Sawka, M. N., S. J. Montain, and W. A. Latzka. 2001. Hydration effects on thermoregulation and performance in the heat. Comparative Biochemistry and Physiology Part A 128: 679-690.

Spaccarotella, K. J. and W. D. Andzel. 2011. The effects of low fat chocolate milk on postexercise recovery in collegiate athletes. The Journal of Strength and Conditioning Research 25: 3456-3460.

Van Loon, L., M. Kruijshoop, H. Verhagen, W. Saris, A. Wagenmakers. 2000. Ingestion of protein hydrosylate and amino acid-carbohydrate mixtures increases postexercise plasma insulin responses in men. J Nutr 130: 2508-2513.

Zambraski, E. J. 2005. The renal system. Pages 521-532 in C. M. Tipton, M. N. Sawka, C. A. Tate, and R. L. Terjung. American college of sports medicine: Advanced exercise physiology. Lippincott, Williams and Wilkins, Baltimore, Maryland, USA.

Hydration and Sport Beverages (Basic)

Athletes have many factors to consider when it comes to improving performance, and a critical aspect is hydration. The human body is about 60 percent water, and water takes part in several chemical reactions within the body (Gropper et al. 2008). Water also allows for transport of nutrients, is essential for maintaining the body’s temperature, and is necessary for most other physiological processes (Dunford and Doyle 2012). Physical activity leads to additional physiological stress, further increasing the need for adequate hydration. With numerous hydration options available to athletes, it is necessary to examine the existing research and recommendations to promote proper hydration for athletic participation.

The goal for hydration status is euhydration, which is a sufficient volume of water to meet the body’s requirements (Dunford and Doyle 2012). Deviations from this condition include hypohydration and hyperhydration, and both can lead to detrimental symptoms (Sawka et al. 2001). Hypohydration occurs by the process of decreasing total body water, or dehydration. Exercise in the dehydrated state leads to several unfavorable symptoms due to the increase it causes in heart rate, core temperature, and perceived exertion responses (Sawka and Coyle 1999). Dehydration, particularly when greater than two percent, can decrease cognitive and exercise performance. The greater the dehydration level, the greater the impairment in functioning (Cheuvront et al. 2003). Hyperhydration involves overdrinking in combination with an agent that binds water. Though sometimes promoted as a means for improving exercise performance, this practice has many risks and is generally not recommended.5 Another concern in this realm is hyponatremia, a condition in which plasma sodium levels are decreased. Symptoms include headache, fatigue, confusion, seizures, coma, and even death (Zambraski 2005).

As has been demonstrated, excessive deviations from fluid balance can have detrimental effects on health and athletic performance. Fluid balance is comprised of fluid loss and fluid gains of the body. The primary routes of fluid losses include respiratory, renal, gastrointestinal, and sweat. In regard to fluid gains or replacement for athletes, recommendations have been developed by the American College of Sports Medicine.

Numerous beverages are promoted as being beneficial for athletes for fluid replacement purposes. Beverages and products often touted include water, sports beverages (Gatorade, PowerAde, etc.), protein drinks, milk, chocolate milk, and caffeinated beverages. Water is likely the best option for before and during exercise when activities are less than sixty minutes. For exercise of longer duration or in extreme environmental conditions, electrolytes and carbohydrates may need to be replaced during exercise in addition to fluid losses. Caffeinated beverages may have potential stimulatory benefits, and do not appear to excessively negatively affect hydration status when used in appropriate amounts. In the post exercise period, recovery beverages such as chocolate milk, protein drinks, and sports beverages may be viable options (Dunford and Doyle 2012). Regardless of the products selected for the means of hydration, athletes should make maintaining appropriate hydration levels a priority in order to maximize their health and athletic performance.

Learn the technical details of hydration and sports drinks.

References

Gropper, S. S., J. L. Smith, and J. L. Groff. 2008. Advanced Nutrition and Human Metabolism, 5th Edition. Thompson Wadsworth, Belmont, California, USA.

Dunford, M. and J. A. Doyle. 2012. Nutrition for Sport and Exercise, 2nd edition. Wadsworth, Belmont, California, USA.

Sawka, M. N., S. J. Montain, and W. A. Latzka. 2001. Hydration effects on thermoregulation and performance in the heat. Comparative Biochemistry and Physiology Part A 128: 679-690.

Sawka, M. N. and E. F. Coyle. 1999. Influence of body water and blood volume on thermoregulation and exercise performance in the heat. Exercise and Sports Science 27: 167-218.

Cheuvront, S. N., E. M. Haymes, and M. N. Sawka. 2003. Fluid balance and endurance exercise performance. Curr Sports Med Rep 2: 202-208.

Zambraski, E. J. 2005. The renal system. Pages 521-532 in C. M. Tipton, M. N. Sawka, C. A. Tate, and R. L. Terjung. American college of sports medicine: Advanced exercise physiology. Lippincott, Williams and Wilkins, Baltimore, Maryland, USA.

American College of Sports Medicine, Sawka M. N., L. M. Burke, E. R. Eichner, R. J. Maughan, S. J. Montain, and N. S. Stachenfeld. 2007. American college of sports medicine position stand: Exercise and fluid replacement. Medicine

Understanding Head Injuries Through Biomechanics and Math

soccer-header

In biomechanics, systems in motion — such as the impact of a ball on a player’s head — are described or “modeled” by mathematical differential equations. For example, these equations can show the relationship between the acceleration or force of the ball to the head at impact, and the change in shape of brain tissue in response to that form. The solution to these equations provides information that could be used to establish new safety regulations or adequate sports gear for players.

Current studies show that heading the ball may not be as much of a concern as physicians and parents thought, although it is not fully understood how repetitive head shooting, through many years of play, affects players. Further research will continue to help treat and prevent injuries, and improve athlete performance through individualized coaching.

Learn more about the basics of head injuries and biomechanics or read the more technical mathematical explanation.

Article by Cristian Clavijo

Fast and Furious: How Muscle Fiber Type Influences Basketball Performance (Technical)

Introduction 

A unique combination of speed, agility, strength, and power sets professional athletes apart from the rest.  Are these attributes genetic, or do they result from hard work and dedication?  In science, answers are rarely black and white and this question is no different.  It is a complex interplay of genetics and training, which sets off a cascade of physiological and anatomical mechanisms, that produces our professional athletes.  These mechanisms are wide in their scope and intricate in their complexity.  Therefore, this article focuses on explaining muscle fiber properties in the context of basketball related performance.  It also presents some training principles to help the athlete improve his or her performance.

Muscles and Contractions 

When we decide to move a part of our body, the brain sends a signal through the nervous system. The signal, carried by motor neurons, then travels to the muscles required to perform the desired action, causing contraction and movement.  Despite this apparent simplicity, much more actually occurs, making this process quite complex.

The neuromuscular junction is the location where the signal from the nervous system meets the muscular tissue.  Motor neurons branch as they approach muscles to the point where only one individual branch innervates a muscle fiber (Seeley et al. 2006).  There is a small gap between the neuron and the fiber called the synaptic cleft.  The signal carried by the neuron causes a release of particles called neurotransmitters into the synaptic cleft, signaling the muscle fiber to fire (Seeley et al. 2006).

On the molecular scale, muscle contraction is a result of what is known as the sliding filament theory (Huxley and Hanson 1954, Huxley and Niedergerke 1954).  Briefly, each muscle fiber houses a sarcomere.  Inside the sarcomere, a thick filament composed of myosin and a thin filament composed of actin reside.   Upon neurotransmitter signaling, the thick myosin protein uses a ratchet motion to move the actin protein and cause contraction (Seeley et al. 2006, Plowman and Smith 2008).  A more in-depth explanation of the sliding filament theory and muscle contraction is given in another article: 95 miles per hour: Performance Physiology of Pitchers.

Muscle fibers are categorized into two groups: slow-twitch (ST) and fast-twitch (FT).  For the purposes of this article, we will consider the most common forms of these two fibers found in the literature.  Type I fibers are ST fibers and type II fibers are FT.  There are two classifications of type II fibers called type IIa and type IIx (Baechle and Earle 2008).  A surface level difference between fast- and slow-twitch fibers is the amount of blood supplied to the muscle.  Type I fibers have a well established blood supply and stain red during histochemical staining while type II fibers have a less developed blood supply and stain white (Zierath and Hawley 2004).  This can be seen in a chicken or turkey where breast meat is white (fast-twitch) and the legs and thighs are dark (slow-twitch).

Type I fibers have a small diameter with a large population of mitochondria, giving them a high aerobic capacity (Baechle and Earle 2008).  This aerobic capacity directly relates to the slow relaxation and twitch times, but also predisposes the muscle to fatigue slowly (Plowman and Smith 2008).  In physiology, structure always determines function.  The aforementioned structural characteristics give good evidence to say that type I fibers are used primarily in weak or moderately strong contractions that must take place over extended periods of time or that occur in a repetitive manner (MacIntosh et al. 2006).

Type IIx fibers are on the opposite end of the spectrum from ST fibers.  These fibers have a large diameter with a low density of mitochondria, thus, their aerobic capacity is low but their ability to function in the absence of oxygen is extremely high (Baechle and Earle 2008).  In stark contrast to ST fibers, type IIx fibers contract fast and hard but fatigue very easily (Plowman and Smith 2008).

In between type I and type IIx fibers are type IIa fibers.  These fibers are essentially a mix of the properties of the two extremes.  Their diameters could be considered intermediate in size and the density of mitochondria is at moderate levels as well (Baechle and Earle 2008).  They have the ability to work in oxygen rich and oxygen deprived situations, meaning they can function in long duration activities and those of shorter, more intense, effort as well (Plowman and Smith 2008).

So, does this information mean that when you want to go fast your body activates FT muscles and when you want to go slow it uses ST?  The answer to this is no: the body evokes a specific pipeline of recruitment to carry out all skeletal muscle tasks (MacIntosh et al. 2006).  The body starts with type I muscles, and then evokes type IIa in addition to type I as the need for contraction increases.  Finally, type IIx fibers can be recruited if the need for stronger contraction continues to grow (Vollestad et al. 1984, 1992, Vollestad and Blom 1985, Zajac and Faden 1985).  However, in specific fast or sudden corrective movements, the body does allow for type II units to be selectively activated (MacIntosh et al. 2006).  This phenomenon can be clearly seen in many reflexive actions.

The body’s specific protocol for muscle recruitment has implications for athletes.  If there are more ST muscles, it will take longer for the force of contraction to grow large enough to recruit more FT fibers.  Conversely, if there are fewer ST fibers, then type II fibers may be recruited sooner in those individuals.  Therefore, we will next look at the distribution of fibers within individuals and athletes.

The distribution of fiber types can vary from one person to another in the same group (Saltin et al. 1977) and depends on the genetics of individuals (Simoneau and Bouchard 1995).  However, scientists do have a general idea of locations in which each fiber type is in high density.  Muscles that contribute to sustained postural activity tend to have the highest amount of ST fibers (Plowman and Smith 2008), whereas the limbs contain more FT fibers (Seeley et al. 2006).  The percent of ST fibers in sprinters has been shown to be more than half that of endurance cyclists (Fox et al. 1993).  Furthermore, it has been shown that these differences can be attributed, to a degree, to sport specific exercise and training (Saltin et al. 1977).  What these data indicate is part of our distribution of fiber types is due to genetics, and some is due to sport-specific training.

Basketball’s Physiological Requirements 

Understanding the training needs for basketball requires more than just knowing about muscle fiber types.  It requires a thorough knowledge of the systems needed during competition.  Therefore, this section will briefly discuss the muscles, energy systems, and recovery principles that contribute to speed, agility, and power on the basketball court.

The upper body demands of a basketball player are greatly inferior to those of the lower body.  For this reason, the focus will be on the lower body only.  The buttocks, quadriceps, hamstrings, and calves play the most significant role in speed, agility and power.  Core stability has been shown to contribute to running performance (Sato and Mokha 2009), so it must be considered as well.

A study done by McInnes et al. (1995) sought to quantify the physiologic load placed on basketball players, lending insight into training demands for athletes.  They found that players change direction on average every 2.0 seconds.  Additionally, they did about 105 high-intensity sprints per game, one every 21 seconds, lasting an average of 1.7 seconds.  Data indicate glycolysis as the primary energy producer, meaning that anaerobic endurance is required.  Furthermore, players had an average heart rate of about 169 beats per minute throughout the game.  All these data led the authors to conclude that metabolic and cardiovascular demands are high in basketball players (McInnes et al. 1995).

Fitness and Training 

It is important to review the needs and goals of a training program designed around a basketball player.  First and foremost, the program must train for FT fiber development in the legs.  At the same time, the anaerobic energy system must be trained to ensure stamina and recovery during high intensity bursts.  Finally, agility (which is the ability to change direction) needs to be incorporated.

Agility training has been shown to increase muscular response times in the quadriceps and gastrocnemius (calves) (Wojtys et al. 1996).  T-drills, lateral movement drills, and balance drills are all components of agility training.  The type and variety of agility drills is endless, essentially any drill that incorporates quick movements with changes in direction in 5-15 second intervals will improve agility, build anaerobic endurance, and develop FT fibers.

Plyometric (plyos) and ladder drills are two effective means of increasing quickness and explosiveness through FT fiber development.  Plyos are generally very rapid, short distance jumps that occur in 5-20 second sets.  Dot drills and four-square setups are the most common.  In both, there is a pattern of dots or numbers on the ground in which the athlete uses one or two legs to hop about the pattern in a variety of ways.  Speed ladders are similar but all movements move the athlete along the ladder, making these drills less stationary.  These two methods are nearly endless in their variety.

Incorporating core training must be done as well.  Swiss ball, stabilization, lower back, and hip flexor exercises work together to build the entire core.  We have discussed that the stabilizing core muscles are primarily ST fibers, so exercises need to be designed with this in mind.  Rapid repetitions are less important here as the body is genetically predisposed to maintain ST fibers in this region (Plowman and Smith 2008).  Long duration core stabilization exercises like leg raises and planks should be the focus.

Finally, it is important to work the training protocol around the previously mentioned activity data from McInnes et al.  These data tell how to design recovery times between sets and between training sessions.  Recovery should never be taken lightly as it is just as important as the actual activity in improving performance.

Conclusion

The principles presented in this article can be applied to a wide range of sports whose demands are similar to those of basketball.  It is important to remember that there are limits to everyone’s abilities.  Most of us will never get close to the level of Michael Jordan or LeBron James, yet each person does have room to improve in some aspect of their game.  The requirements for improvement are simple: hard work and dedication.  With these two ideas in mind, it is nearly impossible to produce a training program that does not improve performance.

 

By: Josh Silvernagel, Graduate Student, Bioengineering, University of Utah
Josh Silvernagel received undergraduate degrees in Exercise Science and Mathematics from Bemidji State University (BSU) in Bemidji, MN.  During his undergraduate studies, he was a four year starter in baseball for the BSU Beavers, where he both pitched and played infield.  In addition to providing sport specific training for ametuer and professional athletes following school, Josh spent two years coaching the sport at both the collegiate and high school levels.  He is currently working on a Ph. D. in Bioengineering at the University of Utah, where he studies cardiac electrophysiology in the CARMA Center.  Josh and his wife, Danielle, are recently married.

Reference:

Baechle, T. R., and R. W. Earle (Eds.). 2008. Essentials of Strength Training and Conditioning, 3rd edition. Human Kinetics, Champaign, IL.

Fox, E. L., R. W. Bowers, and M. L. Foss. 1993. The Physiological Basis for Exercise and Sport. Pages 94–135. Brown & Benchmark, Dubuque, IA.

Huxley, A. F., and R. Niedergerke. 1954. Structural changes in muscle during contraction: Interference microscopy of living muscle fibres. Nature 173:971–973.

Huxley, H., and J. Hanson. 1954. Changes in the cross-striations of muscle during contraction and stretch and thier structural interpretation. Nature 173:973–976.

MacIntosh, B. R., P. F. Gardiner, and A. J. McComas. 2006. Skeletal Muscle: Form and Function, 2nd edition. Human Kinetics, Champaign, IL.

McInnes, S. E., J. S. Carlson, C. J. Jones, and M. J. McKenna. 1995. The physiological load imposed on basketball players during competition. Journal of Sports Sciences 13:387–397.

Plowman, S., and D. Smith. 2008. Exercise Physiology for Health, Fitness, and Performance, 2nd edition. Kippincott Williams & Wilkins, Philadelphia, PA.

Saltin, B., J. Henriksson, E. Nygaard, P. Andersen, and E. Jansson. 1977. Fiber types and metabolic potentials of skeletal muscles in sedantary man and endurance runners. Annals of the New York Academy of Sciences 301:3–29.

Sato, K., and M. Mokha. 2009. Does Core Strength Training Influence Running Kinetics, Lower-Extremity Stability, and 5000-m Performance in Runners? The Journal of Strength & Conditioning Research 23.

Seeley, R., T. Stephens, and P. Tate. 2006. Anatomy and Physiology, 7th edition. McGraw Hill, New York, NY.

Simoneau, J. A., and C. Bouchard. 1995. Genetic determinism of fiber type proportion in human skeletal muscle. The FASEB Journal 9 :1091–1095.

Vollestad, N. K., and P. C. S. Blom. 1985. Effect of varying exercise intensity on glycogen depletion in human muscle fibres. Acta Physiologica Scandinavica 125:395–405.

Vollestad, N. K., I. Tabata, and J. I. Medbo. 1992. Glycogen breakdown in different human muscle fibre types during exhaustive exercise of short duration. Acta Physiologica Scandinavica 144:135–141.

Vollestad, N. K., O. D. D. Vaage, and L. Hermansen. 1984. Muscle glycogen depletion patterns in type I and subgroups of type II fibres during prolonged severe exercise in man. Acta Physiologica Scandinavica 122:433–441.

Wojtys, E. M., L. J. Huston, P. D. Taylor, and S. D. Bastian. 1996. Neuromuscular Adaptations in Isokinetic, Isotonic, and Agility Training Programs. The American Journal of Sports Medicine 24:187–192.

Zajac, F. E., and J. S. Faden. 1985. Relationship among recruitment order, axonal conduction velocity, and muscle-unit properties of type-identified motor units in cat plantaris muscle. Journal of Neurophysiology 53 :1303–1322.

Zierath, J. R., and J. a Hawley. 2004. Skeletal muscle fiber type: influence on contractile and metabolic properties. PLoS biology 2:e348.

 

Fast and Furious: How Muscle Fiber Type Influences Basketball Performance (Basic)

A unique combination of speed, agility, strength, and power sets professional athletes apart from the rest.  This article focuses on explaining how muscle fiber properties produce this combination in the context of basketball.  It explores muscle fiber type properties and some training implications that can be gleaned from what science knows about these properties.

Muscle fiber types fall into two main categories: slow-twitch (ST) and fast-twitch (FT).  Slow-twitch fibers are also known as type I fibers, and FT fibers have two subcategories: type IIa and type IIx (Baechle and Earle 2008).  Type I fibers have many mitochondria which make them able to contract weakly or mildly for long periods of time at low intensities (MacIntosh et al. 2006).  Type IIx fibers have little mitochondria and function to contract very hard and rapidly for short durations.  Lying between type I and type IIx fibers are type IIa fibers.  These have a moderate amount of mitochondria and contract at intermediate levels for lengths of time that fall between types I and IIx (Plowman and Smith 2008).

It is important for basketball players to have large amounts of FT fibers in their legs, calves, and buttocks.  To sustain these muscles over the course of activity, strongly developed ST core muscles need to be trained as well.  Focusing training on these aspects will allow the athlete to meet the high metabolic and cardiovascular demands required of the sport (McInnes et al. 1995).

Agility training has been shown to increase muscular response times in the quadriceps and gastrocnemius (calves) (Wojtys et al. 1996).  Therefore, a combination of balance training, lateral movement training, and T-drill type exercises are important.  Plyometric exercises (plyos) are important for training in this sport.  Finally, core stabilization and recovery principles must be incorporated to maximize gains.

Learn more about the technical aspects of muscle fibers and their influence on basketball performance.

By: Josh Silvernagel, Graduate Student, Bioengineering, University of Utah
Josh Silvernagel received undergraduate degrees in Exercise Science and Mathematics from Bemidji State University (BSU) in Bemidji, MN.  During his undergraduate studies, he was a four year starter in baseball for the BSU Beavers, where he both pitched and played infield.  In addition to providing sport specific training for ametuer and professional athletes following school, Josh spent two years coaching the sport at both the collegiate and high school levels.  He is currently working on a Ph. D. in Bioengineering at the University of Utah, where he studies cardiac electrophysiology in the CARMA Center.  Josh and his wife, Danielle, are recently married.

References:

Baechle, T. R., and R. W. Earle (Eds.). 2008. Essentials of Strength Training and Conditioning, 3rd edition. Human Kinetics, Champaign, IL.

MacIntosh, B. R., P. F. Gardiner, and A. J. McComas. 2006. Skeletal Muscle: Form and Function, 2nd edition. Human Kinetics, Champaign, IL.

McInnes, S. E., J. S. Carlson, C. J. Jones, and M. J. McKenna. 1995. The physiological load imposed on basketball players during competition. Journal of Sports Sciences 13:387–397.

Plowman, S., and D. Smith. 2008. Exercise Physiology for Health, Fitness, and Performance, 2nd edition. Kippincott Williams & Wilkins, Philadelphia, PA.

Wojtys, E. M., L. J. Huston, P. D. Taylor, and S. D. Bastian. 1996. Neuromuscular Adaptations in Isokinetic, Isotonic, and Agility Training Programs. The American Journal of Sports Medicine 24:187–192.

 

The Physiology Behind Performance-Enhancing Drugs (Technical)

Thomas Hicks

What do strychnine, brandy and five eggs have in common?  According to Thomas Hicks, the winner of the 1904 Olympic marathon, these are the essential ingredients needed to be a champion (Jones 2012). While these substances may seem unlikely to increase athletic ability, this is just one example of the extremes that some athletes will go to in order to succeed.

Since the beginning of organized competitive sport, professional athletes have experimented with ways to enhance their natural athletic potential. Even the Olympic creed enforces that desire:  Faster. Higher. Stronger. However, there is a thin line between the development of natural potential and the athletic potential that can only be reached through the use of performance enhancing substances (PES). Now, in the background of every international competition, there is another race, between the ‘dopers’ and the ‘testers’, to see who will be identified as using PES and who will not.

In 1999, the World Anti-Doping Agency (WADA) was formed to assist sport organizers in combatting this problem (Bowers 2009). Funded by the International Olympic Committee and national governments, their mission is to lead the campaign against doping. They are responsible for publishing the World Anti-Doping Code, which includes the Prohibited List and the International Standards for testing and laboratory procedures (World Anti-Doping Agency 2012a).

The Prohibited List, as its title implies, is a list of all substances and methods whose use is not allowed by athletes in competition (World Anti-Doping Agency 2012b). Published annually, this list can be categorized into substances that enhance muscle growth (testosterone and other anabolic-androgenic steroids; AAS) and cellular development (erythropoietin and growth hormones), or are used to mask the presence of the PES (such as diuretics). However, of all the substances included on this list, 60% of the reported adverse analytical findings were attributed to the use of anabolic, or muscle stimulating, agents (World Anti-Doping Agency 2010).

Testosterone and AAS are androgens, sex steroids that have anabolic (muscle development) and androgenic (masculinizing) effects. In normal physiology, androgen and estrogen, also a sex steroid, are the hormones responsible for the development of sexual organs and secondary sexual characteristics.  Males and females contain both androgens and estrogens but differ in the amounts of each hormone that are produced.

Sex steroids exhibit their control on cellular development through the regulation of gene expression.  Androgen and estrogen diffuse into a cell and bind to androgen and estrogen receptors that are circulating in the cell’s cytoplasm (Figure 2). Upon binding, the steroid receptor goes through a conformational change that transforms it from an inactive to an activated state (Saxena and Sharma 2010). The receptor/hormone complex then migrates into the nucleus and binds to DNA at specific DNA sequences, estrogen (EREs) and androgen response (AREs) elements, located in genes whose expression is affected by treatment with sex steroids (Deroo and Korach 2006). These genes are then transcribed and translated into proteins that affect cell growth and development.

In the context of doping, athletes take advantage of the normal physiological properties of androgenic hormones. For example, testosterone has been shown to stimulate muscle mass (Storer et al. 2003), reduce body fat (Bhasin et al 2004) and increase the levels of aggression. By artificially increasing the amount of circulating testosterone in their bodies, athleteswho engage in doping are attempting to enhance the anabolic properties of testosterone while reducing its androgenic properties

Use of exogenous testosterone

One way that athletes abuse anabolic agents is to use testosterone from an exogenous (outside) source. Laboratories test for exogenous testosterone by comparing the ratio of testosterone to epitestosterone, a steroid hormone with no anabolic activity, in urine samples.12  This is known as the T/E ratio. Testosterone and epitestosterone are normally present in equal amounts at a 1:1 ratio; the presence of exogenous testosterone alters that ratio. WADA specifies that an athlete with a urine sample with a T/E ratio greater than 4:1 be investigated further (Thevis et al. 2012). In addition, WADA added epitestosterone to its Prohibited List when athletes started using it, along with testosterone, to equilibrate their T/E ratio.

Use of testosterone derivatives

Athletes engaged in doping may attempt to use synthetic testosterone derivatives that contain various chemical alterations to prevent rapid metabolism (Shahidi 2001). These derivatives are all based on the basic molecular backbone of testosterone and are classified into three categories (Figure 3). Class A steroids, due to 17-b-hydroxy testosterone esters, are more soluble in lipids (fats) and require intramuscular injections. Class B and C steroids are compounds that can be taken orally due to alkylation at the 17-a-hydroxy position or alkylation in the A, B, or C rings, respectively, of the testosterone backbone (van Amsterdam et al. 2010).

Testosterone derivatives are easy to detect in urine samples. The breakdown products created during metabolic processing of these derivatives are not normally present in the body and are an obvious indicator of doping.  In addition, some of the long-acting AAS, such as nandrolone, can be detected for up to 6 months after use (Bagchus et al. 2005).

Use of compounds that indirectly modify testosterone levels

Some athletes engaged in doping may use compounds that are involved in the modification of pathways surrounding testosterone production, thus, indirectly, affecting the level of testosterone in the body. Estrogen is actually derived from testosterone through the activity of aromatase (Kicman 2008), an enzyme that irreversibly converts testosterone to estrogen. Use of an aromatase inhibitor, such as anatrozole, inhibits this conversion, allowing more of the available testosterone to remain intact.

Selective androgen receptor modulators (SARMs) were developed as a means to separate the anabolic effects from the androgenic effects of AAS in order to prevent damage to the prostate in elderly men. SARMs were added to the Prohibited List in 2008 due to their anabolic qualities and potential for abuse. Most of the SARMs that are on the market can be detected in urine samples.

Negative implications of using AAS


When an athlete artificially increases the amount of testosterone in the body, they are disrupting the normal hormonal feedback loop that is necessary for several body functions. Although much is known about steroid hormonal regulation, many of testosterone’s effects on the body are unknown because androgen receptors are expressed in various tissues.

Acute effects from testosterone doping can include fluid retention, gastrointestinal irritation, oily skin, jaundice, menstrual abnormalities, hypertension and infections at the injection site. Interestingly, males using high doses of AAS can have circulating estrogen levels typical of women during a normal menstrual cycle, leading to breast pain in men (Wilson 1988).

Due to the nature of hormone receptor signaling, testosterone use does not produce instantaneous results. Athletes who engage in testosterone doping follow a regimen of long-time use, thus, increasing their chances of developing irreversible adverse affects. Some of these chronic effects include breast development (gynecomastia) in men, loss of scalp hair in women, and increased levels of LDL cholesterol leading to atherosclerosis and cardiomyopathy (Wilson 1988).

The long-term adverse effects of AAS use can be seen in studies of athletes from the former East Germany. During 1960 to 1980, East German athletes were exposed to systematic doping regimens with many athletes being drugged without their knowledge, including young female athletes (Franke and Berendonk 1997). Many now suffer from cancer, epilepsy, metabolic diseases and sudden inflammatory episodes. These detrimental effects have even been transferred to the next generation; children of doped athletes exhibit asthma, allergies and crippled feet or legs at higher incidence rates than the normal population (World Anti-Doping Agency 2012c).

Occurrence of doping

Despite the health risks, the misuse of testosterone, and doping in general, is still prevalent in the athletic community. To prevent doping athletes from competing, WADA estimated that the London 2012 Anti-Doping Laboratory would analyze 6,250 samples and test one out of every three athletes, including all of the medal winners (World Anti-Doping Agency 2012d). If caught, athletes who violate any of the rules of 2012 Olympics Anti-Doping Code would be subject to immediate disqualification with forfeiture of any acquired medals or prizes and could be deemed ineligible for future Olympic competitions (International Olympic Committee 2012). This punishment was recently evident in the case of Nadzeya Ostapchuk, a shot put athlete from Belarus, who tested positive for metenolone before and after her event. The International Olympic Committee disqualified her and withdrew her gold medal (Olympic News 2012).

Based on the immensity of WADA’s response in preparing for the 2012 Olympics, WADA still believes doping to be a formidable issue in organized sports. Even though WADA was created to guarantee equality in sport, its mission is also to support and encourage the health of athletes and the public.  Hopefully, WADA will be able to convince athletes and the public that the use of performance enhancing substances is not worth the risks.

By: Kirstin Roundy, University of Utah

Kirstin Roundy holds a M.S. in Laboratory Medicine and Biomedical Science from the University of Utah. She spent 14 years working as a biomedical researcher studying the gene regulation in B cell development. She enjoys acquiring knowledge and takes random, non-credit classes just so she can learn something new. Her favorite sport is soccer.

References:

Bagchus, W.M., J.M. Smeets, H.A. Verheul, S.M. De Jager-Van Der Veen, A. Port, and T. Geurts. 2005. Pharmacokinetic evaluation of three different intramuscular doses o nandrolone decanoate: analysis of serum and urine samples in healthy men. J. Clin. Endocrinol. Metab. 90:2624–30.

Bhasin, S., T.W. Storer, A.B. Singh, L. Woodhouse, R. Singh, J. Artaza, W.E. Taylor, I. Sinha- Hikim, R. Jasuja, and N. Gonzalez-Cadavid. 2004. Testosterone effects on the skeletal muscle. Pages 255-282 in E. Nieschlage and H.M. Behre, H.M. editors. Testosterone: action, deficiency, substitution, 3rd ed. Cambridge University Press, Cambridge, UK.

Bowers, L.D. 2009. The international antidoping system and why it works. Clin Chem 55:1456–61.

Deroo, B.J. and K.S. Korach. 2006. Estrogen receptors and human disease. J Clin Invest. 116:5 61-70.

Franke, W. and B. Berendonk. 1997. Hormonal doping and androgenization of athletes: A secret program of the German Democratic Republic government. Clin Chem 43:1262-79.

International Olympic Committee. 2012.  Anti-Doping Rules. Retrieved from http://www.olympic.org/fight-against-doping/documents-reports-studies-publications

Jones, D.S. 2012. Olympic Medicine. New England Journal of Medicine 367:289-92.

Kicman, A.T. 2008. Pharmacology of anabolic steroids. Br J Pharmacol. 154:502–21.

Olympic News. 2012. IOC withdraws gold medal from shot put athlete Nadzeya Ostapchuk. Retrieved from http://www.olympic.org/news/ioc-withdraws-gold-medal-from-shot-put-athlete-nadzeya-ostapchuk/172684

Saxena, N.K. and D. Sharma. 2010. Epigenetic reactivation of estrogen receptor: promising tools for restoring response to endocrine therapy. Mol Cell Pharmacol. 2: 191–202.

Shahidi, N.T. 2001. A review of the chemistry, biological action, and clinical applications of anabolic-androgenic steroids. Clin Ther.  23: 1355-90.

Storer, T.W., L. Magliano, L. Woodhouse, M.L. Lee, C. Dzekov, J. Dzekov, R. Casaburi, and S. Bhasin. 2003. Testosterone dose-dependently increases maximal voluntary strength and leg power, but does not affect fatigability or specific tension. J Clin Endocrinol Metab. 88: 1478–85.

Thevis, M., T. Kuuranne, H. Geyer, and W. Schänzer. 2012. Annual banned-substance review: analytical approaches in human sports drug testing. Drug Test Anal. 4:2–16.

van Amsterdam, J., A. Opperhuizen, and F. Hartgens.  2010. Adverse health effects of anabolic– androgenic steroids. Regul Toxicol Pharmacol. 57:117–123.

Wilson, J.D. 1988. Androgen abuse by athletes. Endocr. Rev. 9:181–99.

World Anti-Doping Agency. 2010. Adverse Analytical Findings and Atypical Findings, Reported by Accredited Laboratories. Retrieved from http://www.wada-ama.org/en/Science-Medicine/Anti-Doping-Laboratories/Laboratory-Statistics

World Anti-Doping Agency. 2012a. Sport Physicians Tool Kit. Retrieved from http://www.wada-ama.org/en/Education-Awareness/Tools/For-Sport-Physicians

World Anti-Doping Agency. 2012b. The 2012 Prohibited List. Retrieved from  http://www.wada-ama.org/en/Science-Medicine/Prohibited-List

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World Anti-Doping Agency. 2012d.  Play True. Retrieved from http://www.wada-ama.org/en/Media-Center/Events/WADA-at-2012-Olympic-Games