I haven't followed other Kenya-EPO-Renato-threads too closely, but as I have been in this thread one of Mr. Canova's opponents, I feel need to conclude my own contibution with a slight restatement of my earlier position with following claims (It is another story whether anyone actually reads this attempt to be devil's advocate):
1) There is a strong likelihood that the effect of blood doping (EPO) on perfomance of elite athletes is overstated.
2) There is a strong likelihood that the effect of blood doping (EPO) on Vo2MAX of elite athletes is overstated.
3) Apart from the prevalent use of EPO, there is still very little scientific data that the substance works on elite level Kenyan runners.
In the following parapraphs I will give the reasons for my restatement on the issue.
1.1) It is a scientific consensus that blood doping elevates Vo2MAX and direct performance of endurance athletes. For instance, a 1987 study found that reinfusion of 800 ml of blood cut the 10K time by 69 seconds (~3.5 %) while only elevating Hb by 5 percent. A Swedish study concluded that the actual performance was elevated by staggering 5.3 % with roughly similar increase in Hb.
That is definitely a strong effect, especially for a Hb elevation so low. If we assume that further increases of Hb elevate performance almost linearly, when we take into account high amount of entry of talented Africans, developments in equipment, training methods and track material plus the entry of pacemakers, the speed increase from "clean" 1960s to the EPO-era has been significantly lower than what it should've been, only some 3-4 percentages.
In cycling, one could also point to the fact that the 1972 cycling one hour world record (49,431 m) by Eddy Merckx has been proven to be very difficult or nearly impossible to beat with similar equipment even after the wide range access to EPO and transfusions since 1980s.
2.1) "Most studies investigating the effects of EPO on performance have evaluated maximal oxygen uptakeâ€, states a 2011 reserch paper on the subject, â€When haematocrit is increased from base values to around 50%, Vo2MAX is increased by 8–12%" (Lundby, Olsen, 2011). Due to conflicting data, there should be some doubt whether this effect is seen in elite subjects as the measured Vo2MAX values of elite athletes haven't been significantly higher in EPO-1990s than in earlier decades. For instance, the mean Vo2MAX of elite Swedish male XC-skiers increased only slightly from 1970s to EPO-1990s (85 --> 88, Finnish equivalents 83 --> 86). And one remembers easily Greg LeMond and his magical figure of 92.5 ml/kg/min from pre-EPO late 80s. Still one should keep in mind that the phenomenom could partly be explained by the fact that a bulk of the Vo2MAX data is from OFF-season.
2.2) It is highly unlikely that one could elevate hemoglobin concentration ad infinitum through EPO or blood transfusions with beneficial effects. Finnish Cross-country skier Eero Mäntyranta had hematocrit level of 68 and by plotting some other of his hematological data on classic charts showing the correlation between total hemoglobin mass and Vo2Max, his "theoretical" Vo2MAX should've been somewhere between 8 and 9 litres (ie. ~120 ml/kg/min). I've never seen a figure even close to this in the literature on him with a reliable source even claiming that his Vo2MAX could've been slightly below 5 litres (~72-75 ml/kg/min).
2.3) Apparently the use of EPO has been prevalent in some types of sports and there it was almost impossible to succeed without use of the substance (cycling). Even there it is possible that the positive mechanism has been more to counteract the stress-induced fall of hematocrit than through the hypothethical Vo2MAX turbo mechanism. This is exactly what cyclist Tyler Hamilton tells in his autobiography The Secret Race:
"Was it possible to win a professional bike race clean during this era?... The answer is, depends on the race. For shorter races, even week-long stage races, I think the answer is a qualified yes... But once you get past a one-week race, it quickly becomes impossible for clean riders to compete with riders using [EPO]... The reason is cost, in the physiological sense. Big efforts - winning Alpine stages, winning time trials - cost too much energy; they cause the body to break down, hematocrit to drop, testosterone to dwindle."
From the Vo2MAX elevating mechanism exactly the opposite should be true as one-day races are ridden in a speed much closer to the maximal oxygen uptake and lactate threshold. It is also interesting that speed of TDF didn't fall even after the hematocrit rule was introduced in 1997 and after maximal hematocrits fell significantly (>60 % --> slightly above 50 %).
3.1) I should share a word about the widely touted study on the effects of EPO on Kenyans (Wondimu et all, 2013). After going through the short summary, there were some questionable parts (no blind-protocol, the Scots were far slower athletes then the Kenyans, Kenyans weren't absolutely elite athletes while still had relatively high Vo2MAX mean of 66.0 ml/kg/min).
Then there is the main discrepancy, which the authors also notice - while there was a significantly different hematocrit response between Europeans and Kenyans, (+19.4 % vs. +8.4 %) the performance response in actual time was only slightly better in Europeans (5.7 % vs. 4.5 %). This is suspicious, as the speed increase of Kenyans is strikingly high in relation to the increase of the Hct. Were the response similar with hematocrits elevated still further, the Kenyan group would cut amazingly additional 54 seconds of their 3K time if their mean hematocrit had been elevated up to 60 %, which is hard to believe. The study is interesting, but unfortunately it hasn't been published fully, as far as I know.
(to clarify, Hct increases are in percentages [ie. 19.4 % = coefficient 1.194], not percentage points).
To summarize this post in one paragraph, my reading of the literature on the subject of EPO (blood doping) indicates heavily that the effect of blood doping on elite athletes is at least limited. And because some Kenyans are through their talents the best of the world, there could be the possibility - as Renato Canova points out - that their physiologal responce to elevated hematocrit is different from the rest of us.
I wouldn't follow the path that far, but at least we shouldn't dismiss Mr. Canova's opinion altogether. This is just additional thinking for everyone (including me) who have taken some ideas as granted, perhaps too easily.
Canova is definitely right in his claim that the subject is simultaneously very under- and overresearched as there has been little or no studies on elite athletes and a bulk of the existing literature doesn't even use any blind-protocol at all. Thus German exercise physiologist Dieter Böning points out in a research paper as late as 2010 that "[a]stonishingly we could find only few true double-blind investigations on ergogenic effects of blood transfusion and Epo".
Hopefully we know one day better.
Lundby, Olsen (2011):
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3082090/
Wondimu (2013):
http://journals.lww.com/acsm-msse/Fulltext/2013/05001/D_57_Thematic_Poster___Running_Performance__.107.aspx