Would the Use of Safe, Cost-Effective tDCS Tackle Rather than Cause Unfairness in Sports?
Neuromodulation technologies like transcranial direct current stimulation (tDCS) might enable professional and amateur athletes to reach their respective levels of physical excellence in a safe, cost-effective, and fair manner. Key factors that may assist an athlete in achieving their potential usually include training for many years, often since childhood, and access to a high level of funding. If cost-effective neuromodulation based on tDCS lives up to its promises (regarding safety and efficacy), tDCS can help athletes to learn relevant skills more effectively and thus reach their respective levels of physical excellence more quickly, especially athletes with limited time and resources. Whilst dangerous, illegal drugs such as EPO and steroids can increase performance without training, current evidence suggests that tDCS assists an athlete in improving their performance in combination with training. Given that the World Anti-Doping Association has not made any statement regarding the permissibility of tDCS, whilst access to and popularity of tDCS are constantly increasing, it is important to consider more in-depth if the use of tDCS can be justified. Here, we will outline three key criteria that any performance-enhancing measure must meet if its use can be considered ethical and permissible according to WADA requirements. tDCS must meet our requirements of safety, hard work from the athlete and accessibility. The preliminary evidence regarding its safety, its relatively low cost and the reasonable expectation, that long-term improvements can only be made if its application is paralleled by intense training, justifies its further research in the context of athletic performance enhancement. Moreover, we also consider its potential wider impact, especially how tDCS could help to level the playing field between amateur and elite athletes.
KeywordstDCS Sports Athletic performance Enhancement Ergogenic aid Doping
Enhancement in Sports
Like in all other human endeavours, athletes are striving to be the best they can be at their discipline. The goal of any athlete is to develop their full potential according to the Olympic motto “Citius, Altius, Fortius” (Latin for “Faster, Higher, Stronger”), proposed by Pierre de Coubertin (1894). The main bounds on athletic performance are physiological limitations such as muscle strength or aerobic capacity, influenced by both genetic and environmental factors. These physiological limitations are not reached without years and years of high intensity training. However, being able to perform this high intensity training (i.e. to be able to push one’s physiological boundaries) requires time, money and access to the right training equipment at the right time. Illegal pharmacological performance enhancing drugs (PEDs) that can push an athlete well over his or her physiological limitations have long been part of the world of sports (Hackney 2017). The use of pharmacological doping substances may explain the last burst of performance occurring in the 1990s before a phase of stagnation, when stricter anti-doping regulations came into place (Berthelot et al. 2010). Since doping controls are stricter than they used to be, legal ergogenic aids and especially technological advances that can enhance athletic performance in a safe manner started being sought after. Examples include sleep optimisation systems, hypoxic tents or the promising technology of transcranial direct current stimulation (tDCS) (Nitsche et al. 2008), which we are discussing here. As tDCS may have the potential to increase performance, it is of interest to investigate it more thoroughly for all athletes and the World Anti-Doping Association (WADA), given that increasing performance—in an ethical way—is the primary goal of sport. We will show that tDCS satisfactorily meets several key criteria when compared to other forms of performance enhancement, both permitted and non-permitted (i.e. on the ‘List of Prohibited Substances and Methods’ (WADA 2016)).1 We acknowledge that this argument is based on the best evidence currently available to us. Should new data become available, showing that tDCS no longer meets our proposed requirements, its status as an ethical and permissible2 form of performance enhancement ought to be withdrawn.
Any athlete (elite or amateur) taking illegal substances breaks the sports and medical ethics code (Chatzopoulos 2009). The World Anti-Doping Code (WADC), the first serious attempt to standardise legal norms internationally, recognises doping as officially illegal based on the principle of equal opportunities in competition (Chatzopoulos 2009; WADA 2015). Whilst doping violations do not necessarily constitute a criminal offence3, sanctions normally take the form of ineligibility and the loss of medals, prize money and overriding of rights to compete and reward, which are internal to the sport and its governance (McNamee and Tarasti 2010).
ethics, fair play and honesty,
excellence in performance,
character and education,
fun and joy,
dedication and commitment,
respect for rules and laws,
respect for self and other participants,
community and solidarity.
Whilst some scholars have argued that WADA’s definition of the ‘spirit of sports’ is too vague (Waddington et al. 2013), others consider it as inconsistent (Geeraets 2018), as it could be seen as ‘courageous’ to take a new PED that is not yet prohibited. Moreover, it has been suggested that the descriptors ‘fair play’, ‘honesty’ and ‘respect for rules and law’ cannot be used to determine whether a certain substance should be classified as doping, as an athlete using a drug, that is not yet prohibited, should not be regarded as dishonest (Geeraets 2018). On the contrary, McNamee argues that the definition is still useful to understand the code in aspirational terms (McNamee 2012). Although there are valid criticisms of WADA’s classification system (Waddington et al. 2013; Geeraets 2018), the code represents a practical consensus of what is considered ethical at an international level. Here, we will establish whether tDCS can be used ethically, not based on whether or not it is currently permitted, but if its use is consistent with our interpretation of WADA’s concept of the ‘spirit of sports’ in aspirational terms (McNamee 2012).
Criteria for Ethical Enhancement
Sufficiently safe to use.
Hard work is required to achieve an increase in performance.
Available to most athletes.
In the following, we will justify and use these criteria to provide a framework for assessing if the use of tDCS is ethical by comparing and contrasting it with forms of performance enhancement that are both unethical and not permitted and those that are currently permitted, but that would have to be deemed as unethical based on the framework proposed above.
Our first criterion stems directly from the WADA Code: two out of the three criteria (enhancement, health risk, violation of ‘spirit of sports’) need to be satisfied to prohibit a substance or method. However, since ‘health’ is also a descriptor for the ‘spirit of sports’, any measures presenting health risks should logically be prohibited, as they are presenting a health risk and violating the spirit of sports. Hence, performance-enhancing measures can only be permissible if they do not represent substantial health risks according to the World Anti-Doping Agency Code (WADA 2015). Whilst we acknowledge that all sports entail a certain degree of risk to health and even death, we cannot consider a form of performance enhancement to meet our first criterion of safety if it increases the risk of severe side-effects disproportionately, since we consider avoiding harm as a core value of our society.7 Therefore, the criterion of safety is not only necessary for establishing whether a PEP should be permitted according to WADA, but also to guarantee its ethical use.
Our second criterion stems from the definition of the ‘spirit of sports’ by WADA (2015); specifically, the descriptors ‘character and education’ and ‘dedication and commitment’ imply the importance of hard physical work to enhance the physical skill that is tested in competition. The focus on hard work to attribute value to achievements is in line with the discrepancy in the evaluation of achievements earned through hard work as compared to achievements gained through good luck (Pritchard 2010).
We acknowledge that, regardless of the employed PEP, hard physical work is required both in training for and when competing in a sport at an elite level, as it is unlikely any ergogenic aid could be more effective in a sedentary group compared to one that also undergoes full-time training. However, if a PEP enables those who are sedentary to gain a significant and sustained performance enhancement, we consider it as unethical.
Whilst we agree that it is as important to train smart as it is to train hard, we do not consider hard intellectual work, arguably necessary for developing new PEPs, to meet our requirements for ethical use. This is in contrast to Savulescu et al. (2004) who argue that ‘biological manipulation embodies the human spirit - the capacity to improve ourselves on the basis of reason and judgment’. Based on this, it could be argued that the whistle-blower Grigory Rodchenkov, who revealed that Russia had a state-implemented doping system (Robertson 2018), also took advantage of his abounding creativity and undertook ‘hard intellectual work’ to design his doping programmes, thereby potentially qualifying all his athletes as ethical users. We would like to clarify, that whilst we celebrate ethically sound ingenuity in developing PEPs for athletes, we think that performance enhancement must be related to ‘direct physicality’, should ‘employ decisive whole-body control and whole-body skills’ and ‘contribute to the development of the whole human’ (Parry 2018).
Hence, here we define hard work as training the physical skill that is tested in competition, which contributes to the ‘development of the whole human’ (Parry 2018). Therefore, PEPs that can lead to a cumulative or long-term enhancement of performance in sedentary individuals should be considered as unethical. We shall examine, with reference to currently permitted PEDs, why a short-term performance enhancement without effort from the athlete can be ethically justified in training but should be prohibited in competition.
We will not apply this criterion to practices that are essential for survival in healthy individuals, i.e. eating, sleeping or breathing, as this could conflict with our first criterion of safety. This extends to artificial means of controlling and optimising these essential processes, e.g. protein powders, temperature-controlled sleeping environments or hypoxic air tents, which are exempt from this criterion on the same grounds.
Our third criterion is fundamentally based on concerns regarding social inequalities. If pharmaceutical or technological companies charged high prices for performance enhancers, there would be an even greater divide between rich and poor athletes. Here, we argue that the WADC descriptors ‘respect for self and other participants’ and ‘community and solidarity’ require the drug or technology to be accessible to most athletes competing in the same sport.8
Whilst a wealthy sports team may not harm an athlete’s health, it may still be considered to violate the ‘spirit of the sports’ if they are perceived to be ‘buying success’—achieving a superior level of performance through higher purchasing power. Based on the importance of hard work in evaluating achievements (Pritchard 2010), this practice could be considered as unfair. This is acknowledged by several high-level sporting organisations that actively limit extreme imbalances; for example, the National Football League (NFL) in America imposes a salary cap (Borghesi 2008). This helps reduce the advantage a richer team would gain from offering a salary to an important player that a smaller team would not be able to afford. In a more specific case, a professional cycling team (Team Sky) was banned from brining a motorhome to the 2015 Tour de France (McMahon 2018), where they hoped the expensive luxury would improve sleep, recovery and therefore performance. This was considered to give an unfair performance advantage as it would only have been available to especially wealthy cycling teams. We must therefore consider the impact of a practice or technology on fairness with respect to its cost, and as Savulescu et al. (2004) suggest, promote measures that reduce the imbalance in performance caused by differences in wealth.
Ergogenic Aids in Sports
In general, conventional measures to enhance performance often begin with getting enough sleep or carefully controlling nutrition. High-cost measures include professional support in the form of personalised training, since it is known that there is a great variability among athletes’ performances in response to different training blocks (Timmons 2011; Bouchard et al. 2011; Epstein 2014), and access to specialist training equipment, e.g. advanced motion capture systems. These established practices to increase performance are considered ethical and they meet our three proposed criteria. Unfortunately, many athletes also feel the need to take illegal and unsafe drugs to keep up with the competition. The lure of success with millions of dollars every year in prize money, and in sponsorships and endorsements is too great, whilst the penalties for taking illegal drugs are relatively small: six-month or one-year-ban from competition if doping does not represent a criminal offence (Savulescu et al. 2004). According to Haugen (2004), these factors lead to a prisoner’s dilemma regarding drugs: Unless the likelihood of athletes being caught doping was raised to unrealistically high levels, or the financial gains of winning were reduced to unrealistically low levels, athletes could all be predicted to cheat. Therefore, the enormous rewards for the winner, the effectiveness of the drugs, and the low rate of testing lead to a scenario where everyone is worse off taking drugs as compared to nobody taking drugs (Haugen 2004; Savulescu et al. 2004).
Depending on the chosen discipline, there are different substances that can be used to enhance one’s performance illegally. Here, we classify physiological enhancement drugs as those that have a direct effect on the body’s function, e.g. muscle growth or blood oxygenation, whilst we define cognitive enhancement drugs as those with a more direct influence on the brain, e.g. by enabling greater focus, alertness or relaxation.
Physiological Enhancement Drugs
In endurance sports like marathons, triathlons and endurance cycle racing, a key aim is to increase the red blood cell count, as having more red blood cells carrying oxygen to the muscles improves the aerobic capacity and delays fatigue. This can be achieved by spending many hours running or cycling, training at altitude and using hypoxic air tents. However, the illegal means of blood doping and erythropoietin (EPO) injections, a natural hormone that increases red blood cell production, can lead to better results much more quickly at the potential cost of blood clots, heart attacks, strokes and even death (Thevis et al. 2018). However, if—as some studies (Savulescu et al. 2004) suggest—EPO is safe up until a certain limit,9 it would meet our first criterion on safety.
On the contrary, regarding our second criterion, Sieljacks et al. (2016) found that even in sedentary, untrained healthy men, the ten-week-long administration of EPO led to an increase in maximum power output of 8 ± 3% as compared to 0 ± 2% in the matched control group that was given a placebo treatment. More strikingly, the mean relative increase in VO2 max (l/min) was 15 ± 4% as compared to 1 ± 2% in the control group. They also investigated the combined effect of EPO and a 10-week-long training intervention in the untrained men and found an increase in VO2 max (l/min) of the “clean” training group of 19 ± 4% as compared to 27 ± 6% in the training group under the influence of EPO (Sieljacks et al. 2016). Therefore, EPO administration can clearly increase performance without the need to train, at least in non-athletes. EPO administration in well-trained cyclists also improved their performance in a laboratory test of maximal exercise relative to the control group (Heuberger et al. 2017).
Although EPO might pass the first criterion of safety (when used up until a certain level (Savulescu et al. 2004)), our interpretation of WADA’s definition of the ‘spirit of sports’ (WADA 2015) suggests that it violates the principles of ‘dedication and commitment’ and ‘character and education’, given that significant improvements can be made whilst being sedentary. Therefore, EPO fails our second criterion of requiring hard work to achieve an increase in performance.
In strength-based disciplines such as Olympic Weightlifting, anabolic steroids (e.g. stanozolol) or hormones such as testosterone and its precursor DHEA or Human Growth Hormone are common agents to enhance muscle function and recovery. These substances can lead to heart attacks and strokes, but also to psychological changes such as altered mood, irritability, increased aggression, depression or suicidal tendencies (Thevis et al. 2018). These substances are justifiably not permitted as they fail our first criterion of safety.
Furthermore, to test the effect of testosterone administration on athletic performance, Bhasin et al. (1996) designed a study with four different groups: no exercise + placebo, exercise + placebo, no exercise + testosterone, exercise + testosterone, whereby exercise consisted of controlled, supervised strength training 3 days per week during the 10-week-long treatment period. For both sedentary and training groups as compared to the placebo treatment, the administration of supraphysiologic doses of testosterone increased muscle size and strength. The men in the sedentary group taking testosterone gained nearly as much strength as those that were training regularly but given a placebo treatment (squatting: 19% vs. 21%; bench press: 10% vs. 11%). This undermines the value of the hard training and dedication of the group not taking any PEDs. The testosterone + exercise group made a significantly greater increase in muscle strength (squatting: 38%; bench press: 22%), implying that they gained an unfair advantage relative to the placebo + exercise group. This shows us that this illegal PED has also failed our second criterion of requiring hard work.
Cognitive Enhancement Drugs
Many athletes are not only improving their physiological function, but also try to speed up their reaction times using amphetamines or to achieve better motor control using beta-blockers that can slow down the heart rate substantially, e.g. to help archers steady their shots. Tyson Gay and Asafa Powell, famous world-class sprinters, have both tested positive for the banned amphetamine oxilofrine, thought to increase adrenaline production, focus, alertness and increase oxygenation of the blood (Starkey 2018). On the contrary, beta-blockers (drugs normally prescribed for cases of hypertension) are particularly useful for increasing relaxation and concentration in individuals and it is therefore not surprising that in 2008 North Korean athlete Kim Jong Su was deprived of two medals after testing positive for the beta-blocker propanol (Scott 2018). Whilst amphetamines have a great potential for addiction and can lead to cognitive impairment and severe cardiovascular events, beta-blockers can cause severe blood sugar changes and even heart failure (Thevis et al. 2018). Hence, both PEDs would arguably fail our first criterion of safety. However, amphetamines are allowed in training and prohibited in competition only in all sports, and beta-blockers are only prohibited in training and competition in the two sports that require extreme stability, i.e. in shooting and archery (WADA 2015).
Moreover, neither of these PEPs meet our second criteria when strictly applied, i.e. most likely there would be a significant difference in performance between a group taking these substances and one that does not after a single application. However, we would argue that (if safe) it would be ethical for these substances to be allowed in competition; specifically, if these substances do not have a direct effect on long-term changes in physiology (such as physiological PEDs). Several applications in a sedentary group would not induce any greater increase in performance, as compared to a single application. The key difference here is that a sedentary person who takes EPO for several weeks would achieve a cumulative increase in performance. By comparison, we assume that someone who takes amphetamines would achieve a short and small increase in performance after each application, implying that it would be the same each time in a sedentary person. A larger or longer-term increase in performance would only be achieved by a person who trains whilst under the effect of amphetamines, which may allow for an increased training capacity. In this scenario, the amphetamines are necessary for the increased volume of training, which results in greater performance; however, amphetamines alone are not sufficient for this increase in performance. Therefore, our second criterion does allow for PEPs that do not cause a long-term increase in performance whilst sedentary but do enable greater capacity for training. However, both amphetamines and beta-blockers arguably fail our first criterion of safety and should therefore not even be allowed in training. Therefore, although they are currently permitted, their use should be judged as unethical based on the suggested framework.
tDCS Efficacy and Health Risks
In contrast to the pharmacological performance enhancing drugs (PEDs), tDCS is a novel technology that has been shown to enhance motor learning (Reis et al. 2009; Waters-Metenier et al. 2014), increasing the benefit of training and thereby enhancing performance. The application of weak direct currents to the scalp above the human primary motor cortex (M1) can elicit changes in cortical excitability (Nitsche et al. 2005). Specifically, anodal tDCS can modulate the perceived effort, resulting in reduced perception of effort and greater endurance (Vitor-Costa et al. 2015). Since fatigue can also impair decision-making, response time and skill (Rattray et al. 2015), we can hypothesise the mechanisms of how tDCS could lead to athletic performance enhancement (Edwards et al. 2017) and could be beneficial for the large majority of athletes. However, it is questionable whether recurrent application could help individuals progress beyond the performance enhancement of a single application whilst sedentary.
To date, the majority of studies show that the application of tDCS does not impose any severe health risks in contrast to pharmacological stimulants (Hackney 2017; Bikson 2016; Poreisz et al. 2007). Therefore, considering the lack of long-term studies—to date—it meets our first requirement of safety. Indeed, the scientific community seems to agree on this, whereas the performance-enhancing benefits are still much debated (Angius et al. 2017; Horvath et al. 2015).
Whilst a single session of anodal tDCS has been shown to temporally increase performance in very specific tasks such as the Jebsen-Taylor Hand Function Test (Boggio et al. 2006), or when using small muscle groups (i.e. improving elbow flexors isometric force endurance (Cogiamanian et al. 2007; Williams et al. 2013) or the maximal pinch force of toes (Tanaka et al. 2009)), there are contrasting results when considering larger muscle groups (Lattari et al. 2017; Montenegro et al. 2015; Vargas et al. 2018). Montenegro et al. (2015) did not observe automatic increases in strength of knee extensors and flexors in young healthy subjects, whilst a single session of anodal tDCS has been shown to be related to a temporal increase in isometric quadriceps strength in female adolescent pre-professional football players (Vargas et al. 2018) and an increase in vertical jump ability in men with advanced strength training experience (Lattari et al. 2017). According to a review of the scientific literature by Angius et al. (2017), ‘to date, there are a limited number of studies, showing inconsistent results and often with flawed methodological design’. However, they also point out that when considering all the evidence, tDCS seems to have a ‘positive effect on exercise capacity’. On the contrary, Horvath et al. (2015) collected tDCS data in healthy adults (18–50) from all neurophysiological outcome measures reported by at least two different research groups and based on their assessment could not conclude that tDCS has a ‘reliable neurophysiological effect beyond MEP amplitude modulation’. It is important to clarify that Horvath et al. (2015) only considered neurophysiological outcome measures and not behavioural outcome measures. They conceded that there is a ‘robust literature suggesting tDCS can modulate cognitions and performance on a number of behavioural tasks’ and that ‘it would be a mistake to extend the findings of this analysis to the whole of the tDCS literature’. Moreover, Antal et al. (2015) argue that Horvath et al. (2015) among other ‘important flaws’ have not taken into account the role of critical protocol components such as stimulation duration, intensity, target and return electrode placement and anatomical differences, e.g. (dominant or non-dominant sides). Relevant to the discussion of the use of tDCS to enhance athletic performance, Antal et al. (2015) state that pooling results of 13 min and 26 min anodal tDCS on motor cortex excitability could result in an overall zero effect, since the first condition could enhance excitability, whilst the second one might result in a decrease of excitability due to calcium overflow mechanisms (Monte-Silva et al. 2013).
Given that motor cortical excitability is only expected to last about 90 min after tDCS stimulation (Nitsche and Paulus 2001), it is very unlikely for the effects reported above to last indefinitely. We agree with Colzato et al. ( 2017) that ‘extensive research is needed to verify whether the observed brain stimulation and neural entrainment-induced changes in athletic performance are preserved over time’. Based on the mechanism of tDCS, (i.e. inducing a state of elevated neuroplasticity enabling the brain to recruit muscles better and learn more effectively for about 90 min (Nitsche and Paulus 2001)), recurrent stimulation without training is very unlikely to lead to any significant improvements in motor performance. In fact, we would expect the performance to be the same as after a single session of tDCS. To our knowledge, there has been only one study investigating tDCS without training of the tested body part: von Rein et al. (2015) used mirror visual feedback in combination with tDCS and training of the right hand to enhance motor learning in the untrained left hand of young healthy volunteers. Their interest lies in neurorehabilitation, e.g. of sufferers of unilateral stroke. However, they also argue unilateral motor training in conjunction with tDCS and mirror visual feedback might enhance the training outcome of both, the trained and untrained hand. In this case, however, training is also crucial for making improvements in motor performance.
We would like to remind the reader that our aim here is not to make a definite statement regarding the safety and efficacy of tDCS, which is not possible given the current state of scientific findings, especially because of the ‘diversity of intervention protocols, tasks, and subject groups’ and the lack of ‘strict replication’ studies (Antal et al. 2015). In this paper, we argue whether athletes should be allowed to take advantage of tDCS, if the scientific community were to agree on it being a safe and efficacious methodology. Based on the current state of research, the application of tDCS does not seem to impose any severe health risks and therefore fulfils the first criterion of safety (Bikson et al. 2016; Poreisz et al. 2007; Angius et al. 2017).
tDCS and the ‘Spirit of Sports’
In contrast to pharmacological PEDs like EPO and testosterone that have been shown to improve endurance and strength in sedentary control groups (Sieljacks et al. 2016; Bhasin et al. 1996), training is crucial to make significant changes in performance using tDCS (Edwards et al. 2017). This is the key distinction we want to stress here: As the definition of the ‘spirit of sports’ by WADA implies that hard work is necessary for being able to attribute value to athletic achievements, tDCS should be considered as ethical and permissible, because it is inefficient if not paralleled by intense training.
The administration of tDCS directly before the competition might be considered as gaining an unfair advantage, since many studies have shown that enhanced neuroplasticity, induced by tDCS, most likely leads to better recruitment of muscles such as in vertical jump performance (Lattari et al. 2017). Therefore, we suggest tDCS could be prohibited in-competition only and similar to stimulants (such as amphetamines) be allowed in training (WADA 2015), especially since the majority of studies show that tDCS does not impose any severe health risks in contrast to currently permitted pharmacological stimulants10 (Hackney 2017; Bikson 2016; Poreisz et al. 2007).
The Accessibility of tDCS
tDCS meets the cost requirements of being fair. The most recent tDCS technologies are very affordable compared to other ergogenic aids (Angius et al. 2017). Currently, the two most common tDCS devices (Caputron tDCS, Halo tDCS) are sold for around US $600 each. They represent one-off purchases that can be used in the following years without incurring any additional costs.
As tDCS may offer a far cheaper form of performance enhancement than currently popular and permissible PEPs, we should endeavour to understand its true potential. We would suspect that for most athletes, a tDCS device could cost far less than other permitted ergogenic aids that are designed to improve motor learning such as advanced motion capture systems, which are normally expensive and hard to access.
Our argument relies on the current state of knowledge that there are no severe side-effects in contrast to the use of pharmacological PEDs (Hackney 2017; Bikson 2016; Poreisz et al. 2007) and that the technology is available to all athletes for a comparatively low price. Therefore, tDCS should be allowed in all sports, as potential future doubts in one sport (i.e. health-related results) would affect the overall ethical legitimacy in other sports.
Potential Effects of the Use of tDCS
Levelling the Playing Field between Amateur and Elite Athletes
There are two key factors that have an impact on an athlete’s performance but are usually, at least somewhat, out of their control. These are their physical traits; their height, weight, physiology, ability to learn, as well as the quality (‘How well are they training?’) and quantity (‘How long have they been training?’) of training in their lifetime (Epstein 2014).
Athletic performance is a complex trait that is influenced by both genetic and environmental factors. Physical traits that help determine an individual’s athletic ability are—for example—the strength of skeletal muscles and the predominant type of fibres that compose them, either slow-twitch fibres and fast-twitch fibres. An endurance athlete with predominant slow-twitch muscle fibres will never be able to compete with an equally trained healthy individual that predominantly has fast-twitch fibres in activities that require maximum power or strength. Equally, a sprinter will not be successful in competing at an endurance event against equally trained individuals with predominant slow-twitch muscle fibres (Epstein 2014).
To address limitations (based on appropriate height and body weight alone), sports scientists have developed a measure called the ‘bivariate overlap zone’ (BOZ) (Norton and Olds 2001) that can be used to predict the likelihood that a randomly chosen man or woman possesses a body suitable for elite competition. In terms of appropriate height and weight alone (two complex traits determined by genetics and environmental influences), BOZ analysis revealed that 28% could play professional football, 23% could be professional sprinters, 15% professional hockey players (Epstein 2014). Even if the percentages seem small, there are many people that possess the same physical traits but are not professional athletes, when considering that—globally—there are more than 7 billion people (Worldometers 2017).
Usually, the difference between Olympic athletes and people that have the potential of becoming an Olympic athlete is that the former group starts training at a very young age and that they have access to expensive training programmes and equipment (Mulhere 2018). This is an aspect of performance enhancement that is not accessible to most people that chose to start practising a new sport. Based on the great financial rewards, many countries start promoting athletes at a very young age. On the one hand, the requirement of professional support, specialist equipment, or even weather conditions (such as in winter sports) implies that not all children(/adults) can benefit from being enrolled in training programmes that facilitate the path to becoming Olympic athletes, which could be considered as unfair. On the other hand, the beneficial treatment could come at great costs for the chosen young athletes. Key issues with this system are a) ensuring consent of children, b) ensuring healthy development under the hard training regime and c) ensuring academic and social development (David 2005). In many cases, junior athletes make substantial sacrifices during their adolescent years. Development in other areas (such as academic and social) is often affected by their commitment to the sport (Pummell et al. 2008). However, spending more years at practising the motor skills required for the sport pays off. According to Schumacher et al. (2006), about one-third of all participants in elite cycling World Championships have been successful junior athletes. Successful junior athletes have, in several cycling disciplines, significantly better results in the adult category (Schumacher et al. 2006). We must therefore consider what makes this form of performance enhancement ethical and permissible as it could potentially be seen to fail two of our criteria. We could argue that training children fails as it could be considered as unsafe and as it is only available to a minority.
Therefore, if tDCS lives up to the promise of efficacy and safety, it may help reduce the pressure on teams to recruit potential athletes from such a young age (David 2005; Schumacher et al. 2006). It is highly unlikely that tDCS would be able to make up for several years of training and completely close the gap between a novice adult (although with great potential and ambition) and an adult who has been training since childhood. However, it could certainly help all athletes to make faster progress and therefore steepen their learning curves. If it could contribute to enable an adult to compete on a level that is similar to that of athletes trained from childhood, it would reduce the need for sporting organisations to recruit future Olympic stars from a very young age and could minimise the health, social, psychological and potentially even consent risks associated with putting children on to hard training programmes (David 2005; Pummell et al. 2008). Having less pressure on the junior programmes might enable young athletes to receive a more well-rounded formation, also empowering them to undertake a fulfilling job after their athletic career.
Tackling Obesity and Promoting Healthy Ageing?
Considering the greater context of human society, one of the key factors causing the current epidemic of obesity is an environment that discourages physical activity (Hill and Peters 1998). A key barrier to exercise for most sedentary people is that it takes a lot of time to see significant results, e.g. someone who has no fitness experience and works at a desk all day may need months to learn the technique and gain the fitness needed to perform basic strength exercises. Helping non-athletes see results faster could help increase the number of people who exercise regularly by boosting their motivation and thus their commitment to long-term exercise (Consolvo et al. 2006). Potentially, tDCS might even have a bigger impact in novice rather than elite athletes (Bullard et al. 2011; Edwards et al. 2017). On this basis, tDCS could help improve performance for novice athletes much more than experienced athletes, who already master their motor learning skills and work close to their physiological limits. Moreau et al. (2015) have previously suggested the combined use of tDCS with physical exercise to promote cognitive enhancement. They argue that the combination of tDCS with physical exercise—‘one of the most reliable and well-documented means to trigger general cognitive improvement’—could favour long-term neural changes and durable cognitive improvement.11 If this approach were implemented to help non-athletes enhance their cognition, quality of life and thereby promote healthy ageing, it may be fair to also enable elite athletes to use the same technology.
Whilst we have presented more explicit criteria in contrast to WADA’s vague definition of the ‘spirit of sports’, we have not provided quantifiably perfect thresholds for meeting our criteria. However, the given examples of illegal PEDs have revealed the extremes.
Firstly, we have established that PEPs that substantially increase the risk of death fail our first criterion of safety. We concede that it is difficult to adequately quantify the effect of any practice in increasing the risk of death, as a) even light exercise can increase the risk of death for some “clean” individuals and as b) gathering accurate data on the number of users of any banned practice is challenging due to their illegitimate use. Therefore, here, we struggle with the same problems of vagueness as WADA does. This also applies to PEPs that do not significantly increase the risk of death, but are accompanied by other severe side effects. Quantifying the level of harm of a PEP that does not increase the risk of death is even more challenging. It is possible to give examples of allowed PEPs that have led to the severe long-term harm of athletes, such as the intense and inadequate training of athletes from a young age as previously mentioned. However, we think that our first criterion could also be applied to PEPs with severe side-effects that are not accompanied by a greater risk of death, but this must be consistently established for all PEPs.
Secondly, for our criterion of requiring hard work, we can see that a practice that increases performance whilst sedentary would fail our requirement for the athlete to put in hard work. In the case of EPO and anabolic steroids, the groups that were administered PEDs for 10 weeks, but did not undergo any physical training had a substantial performance enhancement (Sieljacks et al. 2016; Bhasin et al. 1996). We must be careful in how we draw the line between PEPs that cause a small performance enhancement for a short term, and those that cause substantial physiological changes.
Thirdly, regarding our criterion of accessibility, we understand that, although costs are limited to get the tDCS device “once and for all”, it is also true that this technology might soon have upgraded versions of itself (even more so once institutionalised), hence more expensive and therefore more likely to be accessible only to the wealthy ones. Given the limited room for upgrade of tDCS, this scenario is improbable, yet we need to acknowledge it and—in case some variables should change—possibly re-evaluate our opinion on its use.
Considering our suggestion that tDCS could have a positive influence on the obesity epidemic, we acknowledge that even if an easy access to a technology that ensures a speedy improvement in one’s health (fitness) condition is favourable, it is equally true that such nudging attitude from authority should probably start from elsewhere. For example, we might reconsider our working hours, the push on healthy diet and bans on junk food etc. Pushing for an acceptance of tDCS could appear disconnected from reality—unless of course, this would only be one of the moves applied by governments to make us ‘better’. But doubts would then arise over the level of impositions from above on what constitutes the ‘good’ in one’s life.
We must remember that tDCS, especially as a new technology, may still impose certain long-term health risks, even if all studies seem to indicate that they are very low (Bikson 2016; Poreisz et al. 2007). As with any form of performance enhancement, it will inevitably have limits as to how much use is safe. If tDCS were proven to be sufficiently unsafe in some manner, then the case for its ethical use would be undermined.
Some ethical concerns might arise towards the implementation of tDCS in sports and we want to briefly clarify those that we consider most impellent. Firstly, as mentioned already, we do not have in mind any table of sports that should or should not allow the use of tDCS. Following from our argument, it would appear logical to expect the implementation in all sports, as some doubts in one category (i.e. health-related results) will affect the overall ethical legitimacy also in other categories. Secondly, the neuroethical dimension of the administration of tDCS among athletes is a pressing issue. We do not openly envisage an “administration pattern” for tDCS but we certainly suggest a process that will take place when the athlete is fully adult—hence competent to decide how to train and whether to trust his or her trainers with notions (in this case concerning the benefits of the technology and, to this day, the absence of side-effects). Implicit coercion might take place, but this does not differ from any forms of extreme training that are, ultimately, in the hands of specific individuals. It might perhaps be prevented by repetitive informed consent form signature before each session, but also this bureaucratization of our proposal could be neutralised by coaches and trainers if they really wanted. The only antidote is probably the increased awareness that everyone can have about tDCS—and having athletes approaching this moment when they are already full adults should protect them better. Therefore, the right to cognitive liberty is not put at risk in any particular way by our proposal, given that this ‘right to self-determination’ and such a freedom for individuals to control their cognitive processes and consciousness is much less threatened by this tool than by many other means often used with extreme frequency in our society (such as alcohol).
Based on WADA’s Code (2015), we have proposed three explicit criteria to assess if an ergogenic aid should be judged as ethical and therefore also be permissible. Any ethical and permissible ergogenic aid should be safe to use, i.e. be free of any health risks, only work in combination with physical training and be accessible. Whilst the criterion of ensuring health directly stems from WADA’s Code, the other two are based on an explicit interpretation of the concept of the ‘spirit of sports’.
Firstly, the majority of studies agree that tDCS does not impose any severe health risks (Bikson 2016; Poreisz et al. 2007), especially in contrast to pharmacological stimulants (Hackney 2017), that are currently permitted in training and prohibited in competition.
Secondly, specifically the descriptors ‘character and education’ and ‘dedication and commitment’ in WADA’s definition of the ‘spirit of sports’ imply that performance enhancement must be attained through hard work by the athlete, training the physical skill that is tested in competition. When using banned pharmacological PEDs such as EPO and steroids, training is not necessary to enhance performance. In fact, studies have shown that comparable progress was made in a sedentary group taking PEDs and a ‘clean’, active group, training hard three times a week (Sieljacks et al. 2016; Bhasin et al. 1996). On the contrary, we argued here that the underlying mechanism of tDCS, (i.e. inducing a state of elevated neuroplasticity), that can be used to learn motor skills more quickly, seems to suggest that recurrent stimulation in a sedentary population would not lead to any further increases in performance as compared to results obtained within 90 min of the first session of tDCS (Nitsche and Paulus 2001). Therefore, we suggest tDCS could be prohibited in-competition only, due to its immediate effect of temporal performance enhancement, and similar to stimulants (such as amphetamines) be allowed in training (WADA 2015).
Thirdly, hard work is key to the ethical enhancement of performance and this spills over into attempts to limit the impact of finance on sporting success, e.g. by imposing salary caps in the NFL, which is reflected by our third criterion of accessibility. The low cost of tDCS may help reduce unfairness between athletes with high and low levels of funding. Therefore, the low health risks, low cost and potential benefits for society associated with tDCS present compelling reasons to accept tDCS as an ethical and permissible ergogenic aid. We suggest considering new evidence with respect to the criteria proposed here to ensure continued ethical compliance in the use of tDCS. We need to continue investigating further the opportunity that tDCS represents with a—truly—open mind.
Non-permitted forms of performance enhancement are those on WADA’s ‘List of Prohibited Substances and Methods’ (WADA 2016). While ideally, there should be a perfect correspondence between PEPs that are ethical and those that are permitted, as well as between those that are unethical and not permitted, there can be discrepancies. If PEPs can be objectively evaluated as ethical or unethical (rather than relying on WADA’s potential capriciousness in interpreting whether a PEP represents an actual or potential health risk to the athlete and violates the ‘spirit of sports’), ethical PEPs should be permitted, whilst unethical ones should be banned.
Note that, here, we interpret the word ‘permissible’ as recommendation that something should be permitted (in the legal context). Therefore, we would argue that an unethical PEP may well be permitted based on questionable legal decisions but should not be permitted (i.e. is not ‘permissible’) based on our ethical considerations. In line with the ‘is-ought fallacy’, we consider ‘permissible’ to mean ‘what ought to be permitted’ rather than what ‘is’ permitted.
Doping has been criminalised in some European countries (e.g. France, Italy and Slovenia). In some member states of the European Union-related acts such as drug abuse or the smuggling of medicines are also criminal acts (McNamee and Tarasti 2010).
Magnetic resonance spectroscopy (MRS), which can detect changes in the concentration of neurotransmitters and related metabolites, could potentially detect tDCS-induced changes. However, the cost of the procedure is high (about £500 per hour), and it needs to be performed before and after the (possible) stimulation to show a difference. Moreover, the rate of false-positives is high (Davis 2013).
One of the authors has stressed elsewhere how the issue of not violating ‘the spirit of sports’ (or fairness) when using PEDs, does not belong only to contexts of sports, but here the relevance of limiting the analysis to sports is evident (Garasic and Lavazza 2015).
Here, the definition of the word ‘performance-enhancing practice’ implies that the proposed practice is efficacious, i.e. that it enhances performance. Therefore, efficacy is not presented as separate criterion.
Note that in most cases the requirement of safety also implies that there is no increase of performance beyond fundamental physiological limitations, since most fundamental changes to the complex biological machinery of humans also present health risks. If there were any exceptions, i.e. technologies that could push our fundamental limitations (without any health risks), we would also have to consider concerns regarding social inequalities, autonomy and anthropological arguments that are common to the field of neuroenhancement.
Many Olympic disciplines such as Equestrian, Sailing or Track Cycling require the frequent use of equipment and facilities that are beyond the reach of a large proportion of the population; hence, we acknowledge that there are already disparities between different sports. Whilst we do not argue that the disparities per se provide sufficient grounds to prohibit these sports, we should be hesitant to allow ergogenic aids that create even bigger differences between the competing individuals. The idea that accessibility is required for fairness is addressed in Track Cycling, where all equipment used in Olympic-level competition must be commercially available to ensure that no athlete has an exclusive advantage, even though it is often prohibitively expensive (UCI 2018).
If EPO is only used up to a point, where half of the blood is made up of red blood cells, it is considered as safe (Savulescu et al. 2004).
Although these pharmacological stimulants are currently permitted, we would suggest reviewing whether their use can be combined with WADA’s requirement that PEPs do not represent ‘an actual or potential health risk to the athlete’. If established as not safe by a sufficiently large number of scientific studies (and hence also failing the first criterion of safety in the proposed framework above), pharmacological stimulants should be judged as unethical and therefore be prohibited.
Whilst we have been focussing on tDCS of the motor cortex, tDCS can also be applied to other brain regions. It has been shown that repeated tDCS over 5 days (20 min a day) of the right dorsolateral prefrontal cortex could reduce food cravings 30 days after the stimulation (Ljubisavljevic et al. 2016).
Compliance with Ethical Standards
Conflict of Interest
The first author obtained a reduced tDCS device ($200 discount) in June 2017 based on disclosing her scientific and athletic background with Halo Neuroscience. The other authors declare that there is no conflict of interest.
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