Transgender in sport policy is a subject that has been in the news at the youth and high school level over the past few years, but recently entered the international competition discussion with Rachel McKinnon's victory in the UCI Master Track Cycling World Championships. Victory in competition by transgender athletes is not new with Rachel's victory, but success at high-level competition is novel.
There is a wealth of literature supporting the benefits of exercise and that organized sport is one method of getting physical activity. It also is widely accepted that individual and team sports are beneficial in emotional and physical development at all ages of life. Competitive sports are commonly divided to create a field of competition that is fair and equal: biological sex, weight, age, level of competition, and affiliation (1). Biological sex assigned at birth is one of the common metrics used to create fairness in sport competition. With increasing numbers of individuals openly identifying as transgender, rule makers at various levels have sought to create standards that allow for the inclusion of transgender athletes. However, inclusion of the transgender athlete in sport is not well established. Current policies struggle to protect both the integrity of women’s sports and to provide for the inclusion of transgender athletes.
In this review, we will first present a brief history of sex in sport to understand the current metrics used to determine cisgender in sport. Second, we will explore the current state of transgender integration in sport.
Not all readers may be familiar with certain terminology used in this article to describe transgender individuals. For the purposes of clarity within the article, the definitions were selected from the University of California San Francisco guidelines for primary care 2016 (2).
- Gender identity: A person's internal sense of self and how they fit into the world, from the perspective of sex.
- Sex: Historically has referred to the sex assigned at birth, based on assessment of external genitalia, as well as chromosomes and gonads. In everyday language is often used interchangeably with sex; however, there are differences, which become important in the context of transgender people.
- Transgender: A person whose sex identity differs from the sex that was assigned at birth. May be abbreviated to trans.
- Transgender man: Someone with a male sex identity and a female birth assigned sex.
- Transgender woman: Someone with a female sex identity and a male birth assigned sex.
- Cisgender: A nontransgender person (cis, same side in Latin)
Note: “Gender identity is different from sexual orientation” and is different from the sex assigned at birth (3). Sexual orientation, also known as sexual preference, is not in the scope of this article, because it has no influence or relevance in the discussion of fairness of competition in sport. Therefore, this article will not further discuss sexual orientation.
History of Sex in Sport
To understand current metrics used to integrate transgender in sport, it is important to understand the evolution of sex determination in organized athletics. Historically, the underlying reason to divide on the basis of biological sex is to eliminate unfair competition due to concerns that males would masquerade as females to gain an advantage in competition (4). Although well meaning, drawing a line based on biological sex later served to be imperfect at best and problematic in execution.
Dora Ratjen, whose parents raised as a female, competed in the high jump for Germany in the 1936 Berlin Olympics and then went on in 1938 to set a world record at the European Athletics Championships. She was arrested days later at a German train station for “crossdressing.” Documents from the 1930s suggest that ambiguous genitalia led German Reich sports officials to declare Ratjen a male. As a result, Dora changed first names and became Heinrich while Germany returned the medals won and struck Ratjen from the record books (5,6). When Ratjen died in 2008, medical records suggested possible sex uncertainty. It was later speculated that any intent to deceive may not have been overt (4,6). In the same Olympics, the American Helen Stephens competed against the defending Olympic champion, a Polish runner named Stanislawa Walasiewicz (4). After Stephens defeated Walasiewicz, the later accused the American of being a man. Stephens was “examined” and was determined to be a woman although the methodology of examination is unknown. Walasiewicz was later shot and killed in 1980 during a department store robbery. The autopsy revealed ambiguous sexual features (4).
The 1940 and 1944 Olympic Games were canceled due to World War II. In the 1948 Olympic Games, female competitors were required to bring medical certificates from their own physicians to prove their eligibility (4). By the 1966 European Athletics Championships in Budapest, concerns had arisen regarding the factual integrity of these personal physician notes. Therefore, a visual inspection was instituted with an on-site panel of doctors. Because visual inspection was not well received by the athletes, Barr body testing was employed in 1968. This method used the presence of inactive X chromosome (Barr body) as presumed evidence for the absence of a Y chromosome. This testing disqualified Austrian skier Erica Schinegger before the 1968 Olympics (4,7). Before the institution of this testing, Erica Schinegger was a successful women's skier, winning the downhill in the 1966 World Alpine Ski Championships and being named the Austrian athlete of the year (8).
Between 1968 and 1984, there were no known Barr body failures at the Olympic level. However, there may have been other failures detected by national governing bodies before competition, which remain unknown to the public (4,7). Women with disorders of sexual development may have been among those who were not allowed to compete.
In the 1985 World Games in Kobe, Spanish Hurdler Maria Martinez-Patino was disqualified for 3 years before eventual reinstatement (4). Martinez-Patino went on to become a physician. In 2005, she authored a personal account of her experience in The Lancet where she stated, “But I knew that I was a woman, and that my genetic difference gave me no unfair physical advantage. I could hardly pretend to be a man; I have breasts and a vagina. I never cheated” (9).
In 1988, the International Association of Athletic Federations (IAAF) dropped sex testing. The reasoning behind this change included that doping regulations required athletes to pass urine in front of witnesses and modern sportswear was now so revealing that it was considered impossible for a man to disguise himself as a woman (4). The International Olympic Committee (IOC) began testing for Y chromosomes in 1992. During the 1996 Atlanta games, eight women failed the test for Y, but were later allowed to compete. In 1999, the IAAF and the IOC had both abandoned sex testing. By the 2000 Sydney Olympics, there were no blanket tests for sex from the IOC or the IAAF (4).
In 2009, Castor Semenya won the 800-m race at the Berlin World Track and Field Championships. There were no published guidelines regulating sex testing at that time, though suspicion testing remained in place. Given her dominance and muscular build at the age of 18 years, it was requested that she undergo testing. She was determined to be female and allowed to return to competition. Although not known, some have speculated that she possibly has a disorder of sexual development (DSD) (4,10).
The IAAF published the 2011 “IAAF Regulations Governing Eligibility of Females with Hyperandrogenism to Compete in Women's Competition.” Per this regulation:
The expert panel shall recommend that the athlete is eligible to compete in women’s competition if she has androgen levels below the normal male range or she has androgen levels within the normal male range but has an androgen resistance such that she derives no competitive advantage from having androgen levels in the normal male range (11).
For reference, normal male range was considered to be total serum testosterone greater than or equal to 10 nmol·L−1. Therefore, less than 10 nmol·L−1 was required to compete as a female (10).
The problematic nature of this regulation is how to define advantage in the case of a female with hyperandrogenism in the normal male range. It is not specified how a lack of competitive advantage can be proven. If an athlete loses, does that support a lack of advantage? If an athlete wins, have they proven an advantage? Also, if they do not place first, does that negate any advantage they may have brought into the competition?
In 2014, the Indian sprinter Dutee Chand was ruled ineligible due to hyperandrogenism based on the 2011 IAAF regulation. She has an androgen insensitivity syndrome. Chand challenged the ruling in the Court of Arbitration for Sport (CAS). In July 2015, CAS suspended the IAAF regulation for 2 years due to insufficient evidence of advantage. This cleared Chand to race again (12,13). The IAAF published the “Eligibility Regulation for the Female Classification (Athletes with differences of Sex Development)” in April 2018 with an effective date of November 1, 2018 (14). Based on the available evidence, certain events were categorized as “restricted events” in specified international competitions for what the IAAF coined “relevant athletes” (Table 1). Most importantly, the upper allowable limit for circulating testosterone for the relevant athlete is established at 5 nmol·L−1 (15). This stipulation contrasts with the androgen levels allowed in other regulations and policies discussed later in the article.
In a separate release in the regulations section of their web site, the IAAF published “Explanatory Notes: IAAF Eligibility Regulations for the Female Classification.” In this document, they outlined the scientific evidence and reasoning for their latest eligibility and classification standards of the female athlete. A review of available data established normal female serum testosterone falling between 0.12 and 1.79 nmol·L−1 although females with polycystic ovarian syndrome may have circulating levels as high as 4.8 nmol·L−1. For this reason, only DSD or doped athletes would have levels above 5 nmol·L−1 (excluding adrenal and ovarian tumors). Available evidence suggests that an increase in circulating testosterone delivers a performance advantage through a 4.4% increase in muscle mass, a 12% to 26% increase in muscle strength, and a 7.8% increase in hemoglobin. For this reason, the threshold of 5 nmol·L−1 circulating testosterone was chosen instead of 10 nmol·L−1 as will be noted later in this article in other guidelines. The IAAF looked into the question of whether markers, such as height or lung capacity should considered for restriction or relevancy, but concluded “To the best of our knowledge, there is no other genetic or biological trait encountered in female athletics that confers such a huge performance advantage (11).”
Despite attempts to develop standards of sex, several questions still remain. Has sex in sports been clearly defined? Also, is the question of fair and unfair genetic advantage definitively defined? Also, when does someone have an androgen advantage or simply elevated levels of androgens that can be measured? In this backdrop, the second part of this article begins with transgender in sport with the underlying question of fair.
Current Transgender in Sport
In 2017, Jones performed a systematic review of sport participation and competitive sport policies of transgender individuals (16). Of 31 potential articles reviewed, only eight were peer-reviewed research articles or case studies in English. For all eight articles, there were only 147 total subjects, and none of the articles addressed athletic advantage. Jones found that the majority of transgender individuals in competitive sports or sport related physical activity described their experience as negative. Due to the lack of consistent research, Jones concluded that transgender individuals do not have an athletic advantage in sport and therefore, the majority of sport policies are discriminatory due to absence of evidence to support restrictions they have adopted.
The Jones systematic review did not include two important studies for unclear reasons. The first study, by Harper, was acknowledged by Jones, but not included in the systematic review (17). Harper followed eight transgender female distance runners over a 7-year period through self-reported race times before and after transition. Race times were compared using a calculation tool called age grading, demonstrating similar age graded race times before and after transition. Harper concluded:
“As a group, the eight study participants had remarkably similar age grade scores in both male and female sex, making it possible to state that transgender women run distance races at approximately the same level, for their respective sex, both before and after sex transition” (17).
In the article Harper freely acknowledged limitations in the study, such as potential applicability only to distance athletes and inability to apply the results across all sports. The small sample size and unverified self-reported race times leaves the study open to criticism. However, the study design required identification of willing participants, a narrowly defined athletic population, and close to a decade of data collection to complete.
The second article by Gooren and Bunck (18) from 2004 compared 17 female to male against 19 male to female transgender patients before and after transition along the following variables: testosterone levels, muscle mass, hemoglobin, and insulin-like growth factor. While the male to female participants after transition retained more muscle mass than the female to male participants before transition, there was overlap between the two groups. Specifically, the retained muscle mass in the transgender female was within the limits of the cisgender females in the study. The authors noted that height as well as hand and foot size did not change during transition and suggest possible relevance for certain sports.
The IOC policies on transgender in sport entered the modern era in 2003 (19). An ad hoc committee convened by the IOC Medical Commission met in Stockholm in 2003 and consisted of seven members, three from France, two from Sweden, and two from the United States. Their ultimate goal was to issue recommendations on sports participation for those who have undergone sex reassignment in sport (Table 2).
At that time, for transgender athletes to be eligible for participation in sports, the IOC recommended that all surgical anatomical changes have been completed, which included external genitalia, and a 2-year waiting period to be eligible for competition (19). Refer to Table 2 for criteria.
The “IOC Consensus Meeting on Sex Reassignment and Hyperandrogenism” was published in November 2015 (20). In contrast to 2003 IOC policy, this updated guidance stipulated that surgical anatomical changes are not necessary provided that hormone therapy has been undertaken for an adequate time to allow for transition. Those who transition from female to male are eligible to compete as a male without restriction. However, those who transition from male to female are eligible once certain criteria are met. First, the athlete must declare their sex to be female, which cannot be reversed for sporting purposes for 4 years. The athlete must then demonstrate a serum total testosterone below 10 nmol·L−1 for at least 12 months before competition and maintain this standard throughout the duration of eligibility for competition as a female. Monitoring may occur to ensure compliance and in the event of noncompliance, the athlete will be considered ineligible for 12 months.
It is important to note that these recommendations were intended to act as a guide for sports organizations when determining eligibility in male and female competition. These were not binding rules in all worldwide jurisdictions, for individual sport governing bodies, or for national governing bodies. Additionally, the intent of the 2015 Consensus Meeting was not to undermine the World Anti-doping Code and the World Anti-Doping Agency (WADA) International Standards (21). The WADA Therapeutic Use Exemption Committee Guidelines for Transgender Athletes, published in 2017, are available online (22).
United States National Collegiate Athletic Association (NCAA)
Title IX played an important role in the development of women's sports in the United States:
Title IX is a comprehensive federal law that prohibits discrimination on the basis of sex in any federally funded education program or activity. The principal objective of the Title IX is to avoid the use of federal money to support sex discrimination in education programs and to provide individual citizens effective protection against those practices (23).
For this reason, Title IX influences sports competition associated with federal money, but does not apply to professional or international competition that is privately funded. More importantly, sex discrimination does not end at cisgender individuals, but may be seen in the lives of transgender individuals. In the United States, there is a large emphasis on sport competition within the scholastic setting starting at a young age and ending in the university athletic setting. If not simply for ethical reasons, there is legal precedence to apply pressure to organizations to determine how to include all athletes.
The NCAA guidance recognized that the concern about creating an “unfair competitive advantage” on sex-separated teams is a significant and commonly cited reason for barring transgender student-athletes from participation in sports (24). This resistance most often involves transgender women competing on a women’s team:
Some advocates for sex equality in college sports are concerned that allowing transgender women—that is, male-to-female transgender athletes who were born male, but who identify as female—to compete on women’s teams will take away opportunities for women, or that transgender women will have a competitive advantage over other women competitors (24).
Per the NCAA guidelines, such arguments are based on three assumptions. First, transgender women are not “real” and as a result, they should not be afforded equal competitive opportunity. Second, physically being born male grants a transgender women unfair advantage over nontransgender women. Last, men may pretend to be transgender to compete with women.
The 2011 “NCAA Inclusion of Transgender Student-Athletes” upholds 10 guiding principles on the participation of transgender student-athletes. Principles 2 and 3 juxtapose the core of the current challenge for sport policy makers. Principle 2 states that all, “Transgender student-athletes should have equal opportunity to participate in sports,” while Principle 3 stipulates that the, “integrity of women’s sports should be preserved” (24).
A transfemale student-athlete appropriately treated with testosterone suppression may compete on a women's team after one calendar year of testosterone suppression treatment (24). Athletes not taking hormone treatment related to sex transition may participate in accordance with the assigned sex at birth. For example, a transgender female not taking hormones related to sex transition may not compete on a women’s team. However, a transgender male not taking testosterone related to sex transition may compete on a male or female team.
The subject gets more complicated at the high school level and younger. The rules guiding school age student athletes vary by state and sometimes between districts within the states. The case of Mack Beggs in Texas highlights the challenges for local and state school officials in creating rules that are fair for all athletes (25). Mack Beggs, a transgender male wrestler elected to begin transitioning with hormones during high school. Based on the rules in Texas at that time, all athletes compete in their assigned birth sex. As a result, Beggs wrestled in the female category despite being medically treated with androgenergic hormones. Per Beggs, “Even though I was put in this position, even though I did not want to be put in this position, even though I wanted to wrestle the guys, I still had to wrestle the girls (24).”
Since policies vary by state, the web site transathlete.com has links to individual sport governing body web sites for information on sports specific transgender guidance. The web site transathlete.com has a map (Fig.) dividing state policies into four broad categories (26). At the time of this article’s submission, five states still have no state policy. Without standard guidelines at the high school level and below, policy makers will continue to struggle with how to incorporate transgender athletes in sport that is both fair to cisgender and transgender athletes. Per a New York Times editorial from 2017:
“Quite frankly, I don't think anyone has it exactly right because if they did, everyone else would just do that,” said Jamey Harrison, deputy director of the governing body of high school sports in Texas. “If you look at what the NCAA is doing and what the Olympics committee is doing — and those are different because they're largely dealing with adults, versus we are working with minors — it doesn't seem like anybody has landed on something that is universally applicable (27).”
One of the challenges in establishing fair policies in school age athletics stem from age limitations in the current recommended timetables to begin transition. In 2011, the World Professional Association for Transgender Health (WPATH) published their updated Standards of Care, 7th version (28). According to the research presented in this volume, the male/female ratio for sex dysphoric children under age 12 ranges from 6:1 to 3:1. However, evidence suggests that the dysphoria only persisted into adulthood for 6% to 23%. In contrast, adolescents diagnosed with sex dysphoria appear to persist at a higher rate based on the assumption that among adolescents older than age 12 the male/female rate comes closer to 1:1. It has been concluded that younger children may display nonpersistent sex dysphoria. Although the degree of persistence in older children or adolescence has not been extensively studied, the age at which a child can make a self-determination of their sex is unknown and possibly fluid.
This leads to the question of what age to first consider hormone treatment for sex dysphoria. According to the 2011 WPATH guidelines, the adolescent must give informed consent along with the parents if the patient has not reached the age of medical consent (28). The age of parental consent will differ by country. Surgical interventions should not be carried out until the legal age of majority in a given country, and the patient has lived continuously for at least 12 months in the sex role congruent with sex identity.
In 2017, the American Association of Clinical Endocrinologists, American Society of Andrology, European Society for Pediatric Endocrinology, European Society of Endocrinology, Pediatric Endocrine Society, and WPATH cosponsored the “Endocrine Treatment of Gender-Dysphoric/ Gender-Incongruent Persons: An Endocrine Society Clinical Practice Guideline (19).” This Clinical Practice Guideline (CPG) recommended against puberty blocking and sex affirming hormone treatments in prepubertal children with gender dysphoria (GD) and gender incongruence (GI). Adolescents that meet criteria for GD and GI should be initially treated with puberty blocking agents. Initiation should be considered at the first exhibition of changes of puberty. Gonadotropin-releasing hormone analogues are typically administered. In consultation with a multidisciplinary team, sex hormone treatment is recommended to individuals with persistent GD or GI if there is sufficient mental capacity to give informed consent (29). For most adolescents, this is achieved by age 16 years. The guidelines state there may be reasons to start hormones before age 16 years, although minimal literature supports ages younger than 13.5 and 14 years old. Clinical monitoring is recommended every 3 to 6 months, which includes laboratory monitoring every 6 to 12 months during hormone treatment. Table 3 outlines the timeline for the onset and maximum effect of masculinizing effects in transgender males and feminizing effects in transgender females.
For the primary care provider caring for the transgender athletes, careful attention must be given to surveillance of adverse outcomes and long term preventative health and wellness (29). In many cases, this will follow the guidance for the sex assigned at birth, but differences do exist. For example, primary care providers should perform recommended surveillance for breast cancer among transgender females (29).
As noted above, genital affirming surgery is not currently required by the IOC and NCAA guidelines. If an athlete wants to pursue genital affirming surgery, it is recommended after both the treating mental health provider and the endocrine transition provider agree that surgery is medically necessary and that the patient's overall well-being would benefit. Based on the 2017 CPG, the recommended timeframe to consider genital affirming surgery is 1 year after consistent hormone treatment. Full criteria for a sex-affirming surgery, which affects fertility can be found in the Endocrine Society CPG (29).
The topic of transgender in sport has several competing challenges to overcome in the sporting community. While there are published guidelines and rules at many levels, there does not appear to be consensus on standard policies, suggesting that continued rule development will be required. In most circumstances, the medical and scientific community is not required for the development of rules for sport. As an example, medical input was not required to determine that holding in American football is not considered part of fair play. However, in the same sport, medical input has and will continue to be key in rules modifications for the prevention of concussion.
There is a noticeable paucity of medical literature establishing a scientific basis for determining advantage, or lack thereof, for transgender athletes in competitive sport. In defense of the lack of evidence, large population trials looking into competitive advantage will be difficult to conduct secondary to the large number of variables in sport performance. Barriers to completing evidence-based research includes establishing control groups and adequate blinding. Finally, it needs to be stated that being a transgender athlete does not automatically qualify an individual as a potential test subject. Most athletes are never enrolled in research studies, and transgender athletes should be afforded the same respect.
The metrics used to determine the female sex in sport continues to evolve. To quote Harper, “Human biology, however, does not neatly divide into two categories (17).” Currently, female sex for cisgender individuals is determined by androgen levels. However, the introduction of restricted and unrestricted events with the IAAF suggests that even within the cisgender population, there is marked variability between athletes who excel in specific sport events. This implies that individual athletes may tend to gravitate toward certain sports or events based on natural advantages enabled by inborn physiology. The retained height as well as hand and foot size in transgender females reported by Gooren and Bunck (18) may be relevant in select sports such as basketball and swimming. However, cisgender females also can be tall with longer feet and larger hands than the average female, so this trend cannot be viewed insolation.
The IAAF's lower androgen limits for relevant athletes in restricted events may force changes in the lower limits for transgender athletes in other governing bodies. Other variables, such as, but not limited to, V˙O2max, cardiovascular output, and lung capacity, may be retained in a particular transgender athlete, giving that individual an innate advantage over their competition. However, there is no current supporting evidence to confirm or refute the possibility of a yet to be recognized advantage.
The issue of transgender in sport is a bit more complicated than scientific facts or assumptions, because there are social and religious positions in society influencing the rules that govern fair competition. These views vary by world region and within regions across various cultures. Religious views are somewhat independent of, but partially tied to, regions and cultures. These issues impact government rules where competition may be taking place. Additionally, the paucity of scientific and medical literature makes an evidence-based defense of transgender sport competition difficult.
The 2003 IOC guidance included authors only from the United States, Sweden, and France (12). While these authors come from countries with generally accepted economic and political clout, this is not a diverse representation of the larger world. The 2015 IOC Consensus Meeting on Sex Reassignment and Hyperandrogenism authors broadened the world representation (20).
Finally, between national governing bodies, there may be variation for some time. United States Gymnastics in 2018 required sex reassignment surgery to be completed before competitive clearance being granted to transgender female athletes (30). Gymnastics and other aesthetic sports will need to carefully examine their transgender policies since the requirement for sex reassignment surgery before competition is not currently believed to confer a competitive advantage.
In the United States, the variation at the high school level occurs for assorted reasons. In some cases, rules have been outlined at the state level, which could be considered inclusive or exclusive of transgender athletes depending on the state. In other states, a lack of state guidance has pushed decisions down to the school district level to determine, leading to variation between schools on who qualifies as an eligible athlete. This places the governance of fair rules on local school sports officials and team physicians.
The challenges of creating clear rule sets for when a transgender athlete is considered equal for competition purposes becomes more challenging the younger the patient becomes. Assuming the jurisdiction applied the androgen testing principles utilized by the NCAA or IOC, before age 16 years, the transgender male athlete would be forced to compete based under their birth sex as a female, or to compete against cisgender male athletes with a potential androgen advantage. Between age 16 and 17 years, the transgender male athlete would have to choose between ineligibility as a female due to androgen advantage during transition, or compete as a male without the advantage of a full transition. To continue, if a transgender female athlete starts hormones at age 16 years, in accordance with the endocrine society CPG recommendations, that athlete would be ineligible to compete as a female until the age of 17 if a 1-year transition period is required. By age 17 years, most student athletes only have at most 1 to 2 years of eligibility left. The transgender female athlete would then have to compete as a male despite taking hormones that would ultimately make her less competitive with male athletes during the 1-year transition. Depending on the sport and the level of competition, there is a narrow age window that an athlete is considered competitive. Therefore, taking the year of transition could significantly impact the athlete's sport career.
The issue of preservation of fairness in women's athletics is at the center of most questions regarding transgender in sport. Some would argue that this issue presents an attack on the gains made in women's sports over the past century. The history of how science and medicine were deployed since the 1930s to ascertain who is considered female for the purposes of competition highlights that there is still no clear line that is universally accepted as a fair standard for who is female for the purposes of equity in competition. Male competition remains unrestricted. In the opinion of these authors, the male category could be considered the androgen unrestricted category, except where exogenous androgen use (doping) makes the athlete ineligible. The female category is currently the androgen-restricted category. It requires limitations in androgens for athletes whose genotype and phenotype is female, but naturally exceed the androgen levels of much of their competition. It appears that while the male category allows natural advantage to be utilized to the maximum capacity, the female category will, for the time being, be restricted to a set level of advantage or require medical suppression of what could be a potential natural advantage.
In conclusion, establishing equal competition that allows for inclusion of transgender athletes remains a point of discussion and disagreement without universally accepted guidance. The younger the athlete, the more challenging this discussion becomes. Challenges will persist for those making competition rules to create fair but inclusive policies that encourage transgender athletes to participate in the sport of their choice. The medical and scientific community must provide critical input for these decisions. Scientific evidence is sparse. For a variety of social factors, transgender athletes also do not have a positive experience in sports (16). While social inclusion is not part of the rules of most sports or built into the criteria for determining a winner, it is crucial for sports participation. Due to the health benefits for physical and emotional well-being, sports should remain accessible to all.
The views expressed in this article are those of the Authors and do not reflect the official policy of Department of the Army, Department of Defense, or the U.S. Government. The authors declare no conflict of interest and do not have an financial disclosures.