This is part four of a multi-part series titled “Limiting Factors – A Genesis of Blood Doping”. It comes to FasterSkier from Sammy Izdatyev. You can read part one here, part two here, part three here, and part four here.
Sammy Izdatyev is the pen name of a Finnish sports enthusiast and unaffiliated amateur historian, who has been interested in endurance sports since the turn of the millennium. He hopes that his pro bono – research can provide more information into the body of literature of earlier underresearched areas of the history of sports.
Blood doping – a persistent research subject
When Björn Ekblom’s opinion of his 1972 paper was that more research was needed in the arena of blood doping to understand nuances of the subjects, this was to be the case even up to our days. Even when the efficacy of blood doping became the mainstream view by the 1980s, Björn Ekblom’s research on in the arena of blood doping and on the limiting factors of maximal oxygen uptake didn’t end there and his research in both arenas is very extensive.
One question of interest was the interplay between hemoglobin concentration and Vo2Max and total hemoglobin and Vo2Max, which actually was more important in the end? ”Prior research has shown that acute increase in blood volume as such has very little or no effect on work capacity”, Ekblom had written in 1972, and when he looked at the statistical correlations in his first published blood reinfusion study, he had seen that changes in hemoglobin concentration correlated better with Vo2Max than changes in total hemoglobin. The one rare attempt to research how acute blood volume expansion affected performance failed to show any increase in Vo2Max when a large amount of 1000 to 1200 of blood was infused. (Robinson et al, 1966)
Whereas Bengt Saltin had been interested in seeing how cardiovascular system reacted if red blood cells had to flow in less plasma and he dehydrated his subjects in the early 1960s, Ekblom and his coauthor Inge-Lis Kanstrup did the opposite and tested how blood removal and reinfusion and blood dilution with dextrose infusions affected Vo2Max and performance in different combinations. (Kanstrup & Ekblom, 1984)
The results were actually different than what Ekblom had written earlier because even when after dilution (dextrose infusion) each given unit of blood carried less blood, Vo2Max tended to remain the same because body increased cardiac output, indicating that total hemoglobin was more important for Vo2Max than concentration as such. Still working capacity was slightly lower after dilution.
One unintentional conclusion for future blood dopers was that blood dilution was quite an effective in masking blood-doping induced elevation of total hemoglobin, because if one compares the subjects after they had been treated with blood infusion and saline, all the relevant parameters such as total hemoglobin (+6 %), Vo2Max (+ 4 %) and time-to-exhaustion (+13 %) are higher when compared to the control level indicating that they get almost full benefit of the extra RBCs. But the dextrose infusion clearly hides that the blood infusion took place because resting hemoglobin concentration is actually some 7 % lower than the original value (13.7 g/dl vs. 14.7 g/dl).
Another item of interest was the theory of optimal hematocrit, the presumed ”best” value from oxygen delivery viewpoint which was assumed to be roughly hematocrit value of 45 % corresponding hemoglobin concentration of 150 g/l. While particularly Anglo-Saxon blood doping researchers were interested in the optimal hematocrit issue, there is barely a word of speculation about the ”real” optimal hematocrit in any of Ekblom’s writings.
To research this, Ekblom and his coauthors researched how reinfusion of five blood bags (2250 ml) affected Vo2Max and took intentionally subjects with a large variation in their natural values. When a subject with a hemoglobin value of 178 g/l donated blood, his Vo2Max fell significantly even when his Vo2Max could’ve been increased had the optimal value of 150 g/l had any validity. ”The same subject increased his maximal oxygen uptake after the same linear pattern when [Hb] was raised above 200 g/l as one individual with a normal [Hb] around 120 g/l”, the authors observe somewhat surprisingly. (Celsing et al, 1987) It doesn’t automatically follow that if the 120 g/l subject would increase his/her hemoglobin to 200 g/l that Vo2Max would increase linearly all the way through, only that the baseline value is only somewhat unimportant. It could be that every red blood cell increased performance up dangerous zones of blood thickness, and sometimes the ”higher-the-better” idea became the consensus view of the sports circles, true or not.
Not every second athlete could reinfuse five blood bags, but the implication was still troubling, particularly when the prestigious New England Journal of Medicine published brand new information about the new hormone erythropoietin in its January 1987 issue, the exact same month as Ekblom’s newest research was published. When the advent of a synthetic version of hormone erythropoietin sent shockwaves to the sports world in the late 1980s, it still wasn’t quite certain whether a gradual increase in hemoglobin concentration elicited a similar effect as an instant increase. As it is well known, erythropoietin speeds up the production of red blood cells in bone marrow, but it takes weeks until hemoglobin concentration is increased and the human system bolsters mechanisms to fight against this increase if red blood cells are increased above natural level.
While scientists of other countries were interested in the issue as well, Björn Ekblom was the first scientist to research how the red blood cell hormone affected sports performance, when he gathered a group of volunteers with anti-doping specialist Bo Berglund and injected them regularly with the hormone and subjected them to various tests, including Vo2Max and endurance tests.
The results showed that there was little difference between blood transfusion and administration of synthetic erythropoietin (rHuEPO) and both blood doping methods improved performance in an almost identical manner regardless of whether the increase in hemoglobin concentration was gradual (hormone) or instant (autotransfusion). (Ekblom & Berglund, 1991) ”This wasn’t unexpected, but still horrible”, Ekblom described the findings to journalist Omar Magnergård who had written one of the first articles about blood doping almost two decades earlier. ”It also makes it difficult to believe in the future of sports”. (Magnergård, 1989) Ekblom was particularly shocked that only a handful of injections could boost performance so much.
Despite the pessimism of the early-1970s, Ekblom had predicted in the early 1980s that the method to detect autotransfusions would be developed by the 1988 Olympics if there was proper funding and whereas his coauthor Bo Berglund had participated into detection of blood doping with athlete’s own blood, the research ended when EPO replaced transfusions almost altogether by the 1990s.
Now Ekblom took part in the scientific research to develop a method to detect the abuse of the hormone and the team concluded that it was possible to differentiate the natural and synthetic version of the hormone in urine. The method researched and published in 1995 by a group of exclusively Swedish researchers was based on differences of electric charge between naturally occurring hormone and the synthetic version manufactured in a laboratory.
“The method became approved by the journal, but was never used because it was expensive and took up to three days to use being unusable at an Olympics games, championships, etc.”, Ekblom recalls the limitation.
When the idea of how blood doping could even be detected was beyond anyone’s imagination when the issue was discussed first time in media in 1971, there were various approached proposed by the late 1980s and when it became clear that blood samples would be drawn, there was optimism that a few blood samples with good parameters would reveal its abuse. These hopes turned out to be futile even when indirect monitoring of the blood of athletes have at least curtailed the excessive use.
While most of the modern detection methods have been based on how the body reacts to the shortage (blood removal) or abundance (blood reinfusion) of red blood cells, Ekblom’s student and friend Christer Malm from the Umeå University took another type of approach on the issue, looking exactly the blood itself changed during the storage period.
While there hasn’t yet been a breakthrough and the first peer-reviewed published paper showed that the method wasn’t completed, Björn Ekblom is today certain that there will be a method that will detect the abuse. “It feels very good that there will be a method that detects autotransfusions to a 100% degree”, he sees the future prospects of the work of Christer Malm.
Innovator or conveyer or zeitgeist?
As expressed throughout the essay, Björn Ekblom and Per-Olof Åstrand have always maintained that “blood doping” was only as a scientific venue and that the sports application was only an unpleasant ”byproduct” of this research.
“In summary, it is with some regret that I conclude that our basic exercise physiology experiments on manipulation of hemoglobin concentration have some consequences for sport”, wrote Björn Ekblom in 1982 about the subject matter. The evident question is whether these consequences could’ve been postponed or avoided had he not started the ”basic physiology experiments” and the research project on blood reinfusion? (Ekblom, 1982)
While there is almost something biblical about a venomous serpent causing the chain of events that led blood doping to be invented, Ekblom sees that his role in the research is almost accidental and that he was only conveying the ideas of the zeitgeist of the 1960s, because other researchers had also access to the same pre-existing data. “Probably somebody else would’ve done this experiment around that time”, Ekblom thinks modestly about the significance of this blood doping work. “It would be natural that people would think of infusing blood to boost performance. That was something natural at that time”.
Based on the lukewarm reception and the skepticism and on the fact that it took until 10 years before the consensus view shifted conclusively towards the opinion that the method worked, it isn’t that certain how many years attempt in another place would’ve taken. On the other hand, it is true that altitude trained athletes started to break their way into the Olympic arena from late 1960’s onward and athletes showing interest in altitude training, it is possible that the method would’ve been invented even had the research not taken place in Sweden, if the method wasn’t already been “invented” accidentally or in a clandestine research somewhere.
In addition, while Ekblom was quite known and regularly quoted physiologist even in the 1960’s before the blood doping research became the “hot topic”, he still had no idea how overblown the issue would become:
No – I had no idea that this would gather such a speed. I’ve been on the first page in Sports Illustrated which many would give their left hand for. Not even Bengt Saltin or Peo Åstrand has done so. Not that I think it is important – it is more than strange and also shows how the results of the research became taken by the mass media.
Blood doping wasn’t the only seemingly random item turning out something bigger and he finds an interesting parallel from the beginning of the 21st century:
In the summer of 2005 I conducted with a student a little pilot study with administering nitrate on GIH students. We measured many things and the effect was not noticeable except one thing – average blood pressure fell by about 3 mm. Some half years later a little article was published in the New England Journal of Medicine – which is the world’s respected medical journal. Today there are propably some 1000 articles on the effect of nitrate administration on performance, health and mental capabilities. The subject has even its own sessions in large conferences. This history is very similar to that of blood doping, if not bigger.
Ekblom finds this research line “historically very interesting”, and since then, almost every other endurance athletes consume beetroot juice, and there has been research on the effect of nitrates on various other things such as efficiency.
And one should remember that despite the meshing of science and sport with its questionable byproducts, the world of endurance sports wasn’t a pristine paradise before blood doping was invented, and blood doping didn’t “end” it altogether even when there are time periods and sports where it became more a rule than an exception particularly after the introduction of the blood-boosting hormone erythropoietin commonly known as EPO.
Then how much does blood doping increase performance?
When in the introduction we saw that half of the medallists of the 2001 FIS Ski World Championship had highly abnormal values indicating blood doping use, MD Jim Stray-Gundersen who was among the team researching the data read it differently. “Roughly 50 percent of the medalists had such abnormal blood profiles that they almost could only be due to doping”, he commented the issue, ”Half the people who won medals were clean”. (Fitzgerald, 2006)
When blood doping was debated right after the games, Björn Ekblom coauthored an article at that time where the authors claimed the measured hemoglobin values were normal and the differences between (available) ON- and OFF-season data of the Scandinavian skiers didn’t reveal blood doping use. “Nothing talks that Swedish (and Norwegian) skiers would’ve been hematologically doped at the World Cup in Lahti in 2001 or in the last ten seasons”, is their conclusion based on the available data. (Ekblom et al, 2001)
This is somewhat surprising because blood doping considered to be an effective way to boost performance. In fact the handful of published research papers have showed some 2-5 % improvements in time-trial type of performance when hemoglobin concentrations have been increased only by some 10-15 % keeping the values within the healthy ”normal range”, which is in itself an enormous benefit in a race where differences between are usually are occasionally fragments of one percent.
It has also been known that athletes haven’t been so risk averse and some of them have taken multiple of these 10-15 % elevations going far above the normal limits. For instance, from the hematological data from the 1990’s we do know that one successful cyclist had his hematocrit (hemoglobin) increased from 35.7 % (~120 g/l) to 60.7 % (~200 g/l) between winter training season and spring which means that a given unit of his blood theoretically carried some 70 % more oxygen. Even when it is easy to think that these athletes get roughly similar speed improvement with each consecutive 10-15 % elevation, Björn Ekblom isn’t that convinced:
I am not sure about how the other links can keep up. If you go from 140 or 150 g/l to 220 g/l, there must be some compensation in the distribution of flow or perhaps increased blood pressure and so forth.
Björn Ekblom has always maintained that peripheral factors don’t appear to be the main limiting factor if enough muscle mass is recruited, which is illustrated by the fact that maximal ”forced” breathing is almost always higher than the highest values reached during exhaustive exercise points that there is ”idle” capacity in lungs and in addition, the blood returning from the muscles has a very low oxygen concentration, so the oxygen is pretty completely used at the peripheral level.
While blood doping with all the methods has consistently elevated performance in the research papers and Ekblom always has stressed that heart and hemoglobin concentration are the main bottlenecks for most of the people most of the time, it is interesting that Björn Ekblom has occasionally discussed the possibility that the physiology of elites might be different and the key limiting factor might not be the heart and oxygen carrying capacity with elite level athletes.
He brought up this possibility in the mid-1980s in a memorial lecture he gave when his coauthor and even an occasional critic Lars Hermansen had passed away at a relatively young age. ”In some extreme well-trained top athletes with very high maximal aerobic power in relation to the dimensions of the respiratory system the ventilatory/discussion/perfusion complex may be a critical factor – especially at altitude”. (Ekblom, 1986) He held a similar type of opinion quite recently when writing in relation to the ”central governor”-debate that occasionally lungs could limit oxygen delivery of which an ”obvious instance is oxygen desaturation of the hemoglobin in arterial blood during maximal exercise, which seems to be more common in well trained performers who have high Vo2Max”. (Spurway et al, 2012)
In this light, it is also noteworthy that almost all the blood doping research has been conducted with sub-elite level athletes, and improvements can’t be directly extrapolated to elite level athletes.*
*One paper that addressed this issue in 1987 compiling the data from four reinfusion studies with roughly similar protocol actually concluded that participants with 50-65 ml/kg/min were most ”responsive” to blood transfusions whereas subjects with higher or lower baseline Vo2Max increased their Vo2Max only half of the value of that group. (Sawka et al, 1987)
Ekblom’s take on multiple Olympic champion Eero Mäntyranta is also interesting and expresses that he always looks beneath the surface even when anecdotal evidence would support his case. While it is also almost universal consensus view by expressed by geneticists, bioethicists, popular writers and anti-doping activists that Eero Mäntyranta benefited from his super-high hemoglobin concentration, Björn Ekblom isn’t totally convinced about this:
I am not sure about Eero Mäntyranta. His superior ski performance may not be caused by his high hemoglobin. I know that Peo was very much in favour of the idea that his hemoglobin was the reason or his performance.
While there are some issues in making too direct conclusions in comparisons between individuals, Ekblom has noticed a tendency that athletes with very low hemoglobin concentration had extremely efficient blood delivery. He thinks that the opposite could also hold true:
Nobody measured the cardiac output of Mäntyranta, I think. About people who have high hemoglobin concentration at rest, they may have low cardiac output at maximal exercise for other reasons than viscosity reasons. I can say that we found two runners from the Stockholm area who had the same problem as Mäntyranta, so we measured cardiac output in one of these guys and he had fairly low maximal cardiac output, but he had reasonably good oxygen uptake. So there are some strange things going on in the oxygen transport chain.
Ekblom may be on the right track in his skeptical account and there might be other factors explaining the success of the Finn and it is noteworthy that Mäntyranta had good genetics regardless of his high hemoglobin and his nephew Pertti Teurajärvi was an international caliber level cross-country skier who won many medals as a part of the Finnish cross-country relay team, most notably the 1976 gold medal at Innsbruck Olympics. Even when some authors such as author David Epstein (author of The Sports Gene) have stated that he had the same blood phenomenon as his uncle had, this is not the case.
Despite all the media fuss about him, there is very little we know about his aerobic capacity. But as one interesting anecdote, his Vo2Max was discussed in passing in 1971 when he was trying to return to perform at top level for the 1972 winter Olympics and it was mentioned in passing that his Vo2Max had been measured with direct methods only once, in 1965.
According to the journalist, the figure came then back surprisingly low, only 72 ml/kg/min. (Bremer, 1971) That is a good figure – no doubt about it, but nothing enormously high.*
*Well-respected Finnish physiologist Heikki Rusko claimed that the Vo2Max of MaÅNntyranta was estimated to be in excess of 100 ml/kg/min based on an indirect bicycle ergometer test and claiming that it was never measured with direct methods. (Raevuori, 1977)
Case closed on the timeline?
If the reader wondered why the essay is titled “a genesis” and not ”the genesis”, it is because there could’ve been other paths to innovate the method. In fact, the narrative described in this essay on how blood doping became ”invented” is prone to reevaluation even far in the future if and when new information emerges.
It is also difficult to pinpoint a moment when something is ”invented”. Blood doping wouldn’t even be the only hemoglobin concentration – related item that might’ve earlier than widely assumed. Even when there is a lot of truth in the claim that exercise physiologists James Stray-Gundersen and Benjamin Levine invented the so-called “live high/train low”- exercise method in the 1990s, one could argue that the idea was “really” invented some two decades earlier.
Because blood doping researchers Norman Gledhill and Alison B. Froese, in essence, noticed the detraining-problem some fifteen years earlier in their essay.
“A problem with altitude training, however, is that while acclimatizing to altitude, the athlete’s maximum work capacity is reduced approximately 10 %, and therefore, since the intensity at which the athletes can train is slightly reduced, a small amount of detraining can occur”, Gledhill and Froese wrote almost in passing in their 1978 paper. “However, it has been illustrated that it is possible to avoid this problem by transporting the athletes to a lower altitude for their daily training session or by having them train in an oxygen-enriched environment” (Gledhill & Froese, 1979)
The study they refer to where these shortcomings were avoided was published in 1980 and the preliminary report in 1976. If one looks for trails of the idea of intermittent hypoxia even further in time, the idea is mentioned before the 1968 Olympics in a transcript of a discussion that took place about high altitude training between the scientists from nordic countries. ”There is one interesting aspect which is not clearly answered as yet, and that is the effect of intermittent living on a high altitude”, physiologist Kaarlo Hartiala mentioned in passing in 1966 when discussing the matter with his nordic colleagues. “It might be to some benefit to keep the training on a lower and the living on a higher altitude”.
Still, it took until the 1990s before the Stray-Gundersen and Levine ”invented” the idea and gave it the scientific validation. About blood doping, the situation is slightly different because there is some smoking gun research, but in addition, there is also some gossip and evidence about the method actually been used before the 1970s and it is possible to locate some references of athletes having blood doped before the 1970’s even in academic publications. One theory actually is that Ekblom, Åstrand, Goldbarg and the others only gave the scientific validation to the method already in use.
“Among other variables, Åstrand and his Swedish colleagues paid attention to blood values, in particular, the oxygen-carrying ability of hemoglobin”, wrote Finnish historian Erkki Vetteniemi recently about the origins of the blood doping research. “In 1971, one of them (Björn Ekblom) discovered the blessings of blood transfusion for athletes – or, he claimed to have discovered the benefits of blood packing”. Referring to the earlier gossip about transfusions taking place before that, the historian continues that a ”more probable scenario is that the Swedish scientists published their blood packing paper as soon as the method had become commonplace in skiing and other sports”. (Vettenniemi, 2017b)
Vettenniemi has occasionally brought up the case Jonny Nilsson, for whom when Ekblom allegedly offered a transfusion in 1966, but another alleged blood doping case of interest he has mentioned took place early as 1948 before the London Summer Olympics. The incident was mentioned in one of his articles by MD Inggard Lereim, who was since the 1970s has been a Norwegian team doctor and later a member of the FIS Medical Commission. (Vettenniemi, 2017a; Lereim, 2001)
It is equally true that there is some confusion about the timeline amongst the ”in-the-know” Nordic MDs. For instance anti-blood doping activist researchers Tapio Videman, Inggard Lereim and James Stray-Gundersen (and coauthors) wrote about the origins of blood doping in passing in one of their research papers in 2000 that “[r]umors about the use of blood doping have been circulating since the 1960s” (Videman et al, 2000). Only three years later the same trio contradicted this timeline by a decade, writing that ”rumors and reports of transfusion use in endurance sports did not surface until the late 1970s” (Stray-Gundersen et al, 2003). Bengt Saltin on his part coauthored paper in 2012 stating that ”[b]lood doping practices in sports have been around for at least half a century”, indicating the starting point closer to the early 1960s if not earlier. (Lundby et al) This hasn’t precluded Saltin stressing occasionally the importance of the GIH-research line that Ekblom and Åstrand had started in the mid-1960s. (Saltin, 1995)
The case that the GIH-scientists knew about the benefits of blood doping before Björn Ekblom started the research around 1966 is a possibility but still somewhat unlikely one because why would Bengt Saltin have discussed transfusions publicly in 1965 if administering transfusions was the exclusively secret weapon of the Swedes? And why were there many foreign researchers involved in the research and why were the findings discussed as early as 1966 with some 200 nordic physiologists possible hearing about the line-of-inquiry even if the results were inconclusive at best?
If there is one lesson from this lengthy essay, it is that all transfusions aren’t created equal and even if individual athletes had been administered transfusions, it didn’t necessarily mean that the rationale was to ”blood dope” in the same intellectual tradition that later (1971-) athletes performing similar operations did, because anemia was a medical condition treated with transfusions and it could’ve been used for altitude adaptation. It is still noteworthy that the gossip about these pre-1970’s transfusions are a few in number and later impressions of teammates and competitors can be deceptive.
About evolving recollections, multi-time Olympic gold medallist Eero Mäntyranta was furious in 1972 after the Finnish team underperformed at the Sapporo winter Olympics demanding an explanation why the Finnish sports bodies were reluctant to test how blood doping worked to “sacrifice” one of the eight Finnish male cross-country skiers as a guinea pig for the games. “Such a test would’ve been extremely valuable, but still a very modest one, when compared to the enormous medical testing one, hears having been conducted in the modern sports world by the big sports countries”, he wrote in the spring of 1972 shortly after the unsuccessful winter games. (Mäntyranta, 1972)
When blood doping practices were discussed once again in the media in 1985, some thirteen years later, he had a very different timeline and suspected that his Finnish compatriots had blood doped even for the 1966 FIS World Championships, some six years before he wanted the method to be tested. “I don’t want to insult anyone, but there was something strange when some Finnish skiers were in top form at the 1966 Oslo Championships but vanished after the games altogether”, he said. (Mörä, 1985)
It isn’t even certain that even honest recollections about transfusions are sound, because anemias were regularly treated with iron shots and the Swedish daily newspaper Expressen went so far to even describe the treatment of cyclists of the 1970 Tour de France as “blood through drop” while still describing the actual content as “sugar solution and iron”. In addition, there existed some blood reinjection treatments such as ozone therapies that were already in use in the 1960s, and it is known that perhaps the best cyclist of the era Jacques Anquetil believed in the method. “While Anquetil did engage in a form of blood manipulation, it would probably be incorrect to refer to it as a transfusion”, was journalist Feargal McKay’s reading of the treatment in his essay on the history of transfusions in cycling. “What he was actually playing with was super-ozone therapy, whereby a small amount of blood is extracted, treated with ozone and immediately re-injected”. (McKay, 2013)
It isn’t even certain that all the post-1972 transfusions were conducted in order to assume supranormal hemoglobin concentration was beneficial in every condition. Interestingly even cyclist Eddy Merckx (who was offered a transfusion in 1972) mentioned later that his “target” hematocrit was only 52 % when was planning to succeed in his attempt to break the hour world record at altitude, which was in the normal range of residents of 2200 meters and meant that his quest to thicken his blood wasn’t open-ended with the almost “higher-the-better” attitude of the 1990s. (Thirion, 2012)
If one also follows the roots of many known blood doping circles, the roots are usually one way or another traceable to the research conducted at the GIH. The Finns were aware of the Swedish research on some level by the late 1960s and endurance running coach and anti-doping activist Alessandro Donati has also claimed that the Italians didn’t ”know” about blood doping all along but started their research on the subject in the 1970s.
There is a negligible amount of material about the blood doping use by the East Germans, and when the evidence of the Soviet Union blood doping program was revealed, it also looks as if they started their clandestine blood doping research in secret in the mid-1970s as a response to the Swedish research. (Kalinski, 2003)
If they had known it all along, why reinvent it again?
As far as I know, this has been a first deep look into the origins of blood doping, which is somewhat surprising, considering that the blood doping research at the GIH began over fifty years ago, and the first published research paper on the subject was published some forty-seven years ago.
The reason might be that the method of blood doping is so simple and tautologically true that many commentators looking the subject with the modern knowledge erroneously assume that there was not that much to be researched at all in the subject and correspondingly there was barely any debate at all about its efficacy.
If the first blood research paper published in 1972 was an interesting and somewhat unpolished paper on an arena not much researched before, opening the subject for further interest, I do hope that this essay will serve somewhat similar purpose for the subject of the history of blood doping, stimulating intellectual curiosity for “real” historians and researchers either to confirm or debunk my findings and conclusions and to pursue new avenues of research.
Regardless of what the response will be, I do hope that I’ve done justice for the research work that took place at the GIH and elsewhere many decades ago about the topic.
And when I have a huge respect towards Björn Ekblom, I do hope that I’ve proven him wrong when he once remarked that only a physiologist understands the research they are doing.
The author wishes to thank Dr. Björn Ekblom without whose help this essay would not have been possible and also Alex K. and Chelsea L., both of whom went through parts of the first version of the manuscript and corrected grammatical errors and made some improvements into the structure.
This is part five of a multi-part series titled “Limiting Factors – A Genesis of Blood Doping”.
The full bibliography for this research can be found at the end of Limiting Factors – A Genesis of Blood Doping (part one).