But, with the Tour de France coming up over the next three weeks, I figured there would be plenty of time to talk cycling, so keep an eye out for some ‘behind the scenes physiology of the Tour de France in the upcoming three weeks.
But for today, I thought I would go back to something that came up about 2 weeks ago, during a post on EPO use. Lei asked about altitude training, so I figured I’d do a short post on the benefits, if any, of training at altitude. And then Jonathan could follow up with some more information.
As I’m sure many of you know, most elite athletes now do some sort of altitude training before major competitions. I’m not 100% sure where the concept began and how it was realised that a period of altitude training might improve performance. I suspect that it was a result of the opposite being true – when athletes from sea level went UP to altitude, their performance suffered badly – I’m sure many of you can relate! The most vivid illustration of this was the 1968 Olympics (the year of Bob Beamon’s mammoth long jump record, thanks in part to the thin air in Mexico City), when Ron Clarke of Australia collapsed and nearly died from altitude sickness sustained during the grueling 10,000 m race final. It was reported that he suffered permanent heart damage from this event.
In addition to this, there was the obvious experience of mountain climbers who would feel vast improvements in their condition having spent a few days acclimatizing to high altitude, and then returning to slightly lower altitude. So it’s not all that surprising the people felt there was a possibility that training at altitude would improve sea level performance. And that’s what this post is about – we investigate whether this is in fact the case.
First question – what is the basis for altitude training?
Should it even work?
OK, so this might seem like a silly question, but in fact, it’s quite key to all of physiology. The theory behind exercise, until relatively recently, is that you have to slow down because your heart is unable to pump enough blood (and hence oxygen) to the muscles. The result is that the muscles become what science calls “anaerobic” (without oxygen), and they accumulate lactate, eventually forcing the athlete to slow down. The root cause of all this, of course, is a lack of oxygen supply to the muscle – demand exceeds supply, and you get “poisoned” by lactate.
However, there are a couple of pretty major flaws with this theory. I won’t go into them in detail here, but let’s just say that it’s unlikely that the heart is ever unable to supply enough blood. And if the muscles ever ran out of oxygen, they would go into a state of rigor, where they’d stiffen up and not relax properly. And this doesn’t happen, so there is something wrong with this picture. However, it is the basis for why altitude training would work, and so we’ll stick with it for now.
So the theory is that at altitude, your body adapts to the lower oxygen pressure in the air, and these adaptations ensure more oxygen delivery to the muscles. The main adaptation is that the body naturally produces more EPO, which means more red blood cells, as we said in our previous post on EPO use.
And more red blood cells means more oxygen in a given volume of blood, which means longer for the muscles to run out and delayed lactate accumulation, and so on. There are some other theories and adaptations, but we’ll keep it short for today!
So does altitude training work?
Knowing the basics of the physiology, the next question is does it work? This is a slightly controversial one because the science and the anecdotes don’t agree. The athletes swear by altitude training, the science has often failed to find an effect when studies are done in a controlled way. And that’s what we need to consider.
The burden of scientific stringency
The first thing to remember about scientific studies is that they impose a stringency on the volunteers that may or may not make it easier to find a difference. In otherwords, a proper scientific study has to control all sorts of variables that would possibly influence the outcome, and in the case of altitude training, it’s quite possible that controlling these variables will prevent a positive result from being found. For example, a normal altitude training excursion is remote, allowing the athlete to escape his or her normal routine, train perhaps three times a day, away from the distractions of normal training. And this change in approach has often been cited by scientists as the reason that altitude training works. A scientist by the name of John Hawley once wrote an article called “Altitude or Attitude?”, and he claimed it was the attitude change of an athlete going to a dedicated training camp that made the difference, and it would not have mattered if it was 3000 m or sea-level.
Another issue is statistics. In science, a difference in performance must be shown to be statistically significant, which means that it is not due to chance. And science sets all kinds of limits or confidence ranges on a result, and this influences its interpretation. So for example, a 10 second improvement in a 5 km time-trial might be found to be insignificant in a scientific study. However, there are athletes all around the world who are training for 3 hours a day to find those 10 seconds, so there is sometimes a difference between what is a “Statisticially significant difference” and a “Real difference”. A sports scientist and statistician in New Zealand, Will Hopkins, has developed a new method of stats where he looks at something called “Meaningful difference” and this might be the key to understanding and interpreting altitude physiology.
So despite the inability of science to find an effect, my feeling is that there is still something to altitude training, so we need to dig a little deeper. There is a physiological basis for why altitude training would NOT WORK, and that’s important to consider. Remember that the theory is that at high running or cycling intensities, the demand for oxygen supply becomes great enough that the body cannot meet that demand and you slow down. This means that the high intensity running sessions are limited by oxygen. And when an athlete is as altitude, this limit is even greater. So what happens, then, is that an athlete at altitude gets benefits from the increase in EPO and red blood cell mass, but they are actually disadvantaged when it comes to doing the higher intensity training sessions. They simply cannot train hard enough at altitude, and that may offset any benefits they could have derived the other way.
This is the reason for the development of the “live high, train low” theory. What athletes began to do was to find locations where they could live at a reasonably high altitude, sleep there and do all their easy running so that they got the benefit of increased red blood cell levels from EPO. But they trained at low altitude, coming down from their ‘mountain tops’ to do their harder training sessions. Obviously, this is a massive logistical issue – how many locations are there in the world that allow you to drop down from an altitude of 2000m or higher to an altitude of 1000 m or lower to train? But then technology stepped in, and altitude tents and hypoxic houses were developed. This meant that an athlete could sleep at sea level, but in an altitude tent that simulated an altitute of about 2500 m, but then wake up in the morning and head out for a training run at sea-level! And everyone was using them – Paula Radcliffe, Lance Armstrong, the Australian Institute of Sport, Jan Ullrich (apparently). The World Anti-Doping Agency even considered banning them at one stage for the ‘unfair’ advantage they might give!
But the evidence suggests that this live-high and train-low theory does work,though the effects are relatively small. There is also an interesting phenemenon of “responders” and “non-responders”, with some people showing improvements of about a minute over a 5km time-trial after a 4-week training period, while others show no improvement, or even get slower. So the jury is still out, scientifically at least. But the fact that so many athletes swear by it is a sign that there is something there, even if it is just a placebo effect.
The paradox of performance
Which events should benefit most and which do?
One last thing to consider and perhaps this is the most interesting thing about altitude training – there is a paradox about which events are improved most, compared to which should be, according to the theories for why altitude training should work. Remember, we’ve said that the theory behind altitude training is that it improves the body’s ability to deliver oxygen to the muscles. So in theory, this means that it should have the greatest effect on events where oxygen supply is likely to be limiting. Which events are these? Well, in a marathon, the evidence suggests that athletes are running at about 70 to 80% of the VO2 max, which means they are not actually at that limit. Yet altitude training is supposed to work for the marathon!!! Even in our Comrades Ultramarathon, the Russians who regularly arrive and clean up the medals credit altitude training as a reason for their success – Comrades is done at 50% of maximum oxygen use, so clearly, if altitude training is working, it’s working well below the apparent limit. And the current understanding of physiology does not allow us to explain this observation. The same goes for what happens when races are run at altitude – the one where performance suffers the most is the marathon, even though it’s not limited by oxygen in the first place! The 10000 m event, which is done at about 90% to 100% of VO2max, and the 5000 m, are affected much less by altitude or altitude training, and so clearly, we’re missing something as scientists here!
Take home message is that when someone tells you they know the answers about altitude training and why it works, you can quite rightly challenge them, because a lot doesn’t quite add up. But altitude training works, there’s little doubt about that, but apparently only in some people and under some conditions. One of the great things (or not so great…) about science is that there’s always a “but”….!!
Ross and Jonathan