Why altitude training is not always successful.

A new analysis casts doubt on the idea that people are born as "responders" or "non-responders" to training in thin air. To understand the latest data on altitude training for endurance athletes, it is worth looking back at a seemingly unrelated study published in 2015. In it, 1,000 subjects followed a three-month training programme to see if it would lower their blood pressure. The average change in diastolic blood pressure was indeed a clinically significant reduction of five mmHg, which is good news. But not everyone benefited equally. This is what the individual results looked like, with positive and negative changes in blood pressure on the vertical axis:


( Illustration: experimental physiology )

On the left-hand side, some subjects - call them super-responders - saw a drop of more than 20 mmHg. On the right, we have some non-responders, and even some negative responders, whose blood pressure increased by more than 10 mmHg. That is bad news, and if you have it, you might be understandably tempted to sign up for one of those genetic tests that promise to tell you how you will respond to exercise.

Here's the thing: this data is fictitious. It was generated by researchers to illustrate what can go wrong when you try to classify people as responders or non-responders based on a single set of measurements. They took simulated blood pressure data and subtracted exactly five mmHg from each person's baseline value. But to simulate real-world conditions, they also added a random measurement error to both the pre and post values. For some people, their apparent baseline measurement was slightly higher than the actual value; for others, it was lower. The same applies to the final measurement. If you had a randomly low baseline and a randomly high final value, it looked like you were a non-responder - even though everyone in the simulated study was really a responder.

This question of responder and non-responder has been a controversial topic in exercise science (and health in general) for at least several decades. Researchers have rightly recognised that individual variation is as important as the average response to an intervention. But that creates the temptation to label everyone in a study who does not respond as a non-responder. It's like turning over ten dimes and saying, "Look, dimes always land on heads, as long as you ignore those five non-responders."

Which brings us back to altitude training. Since the first live-high, train-low protocols were devised in the 1990s (with the first study showing 17 out of 39 subjects improving their 5,000-metre times), there has been a widespread belief that some people are responders and others non-responders.

But, as mentioned above, you can't really sort responders from non-responders based on a single stage at altitude. To their credit, altitude researchers have been trying for decades to identify the factors that predict whether you are likely to see an increase in oxygen-carrying haemoglobin, which is the main goal of altitude training for endurance athletes. But the results have been mixed at best, and it is still not at all clear whether an athlete who responds to one altitude training program will respond to the next.

That is the long-standing controversy addressed by the latest data on altitude training, published in the Scandinavian Journal of Medicine and Science in Sports . It comes from a group led by Ari Nummela of the Finnish Research Institute for Olympic Sports and again analyses data from 59 national team endurance athletes (cross-country skiers, runners, swimmers and several others) who completed a total of 82 altitude training camps. between 2009 and 2015. The internships lasted between 16 and 42 days, at altitudes between 4,400 and 8,200 feet (1,350 and 2,500 metres).

"Success" was defined as an increase in total haemoglobin mass of more than 1.7 per cent, which exceeds the typical error inherent in measuring haemoglobin mass. Overall, athletes had successful placements in 46 out of 82 cases, for a hit rate of 56 per cent. That may not seem impressive, and ( as I wrote earlier this year ) some scientists would argue that you would see something similar if you simply sent the athletes to a super-focused training camp in an idyllic sea level location, no altitude required. But if you assume that altitude works, you have two possibilities: either some athletes are not suited to respond to altitude, or half of them did something wrong.

To address the first possibility, we can look at the 15 athletes who participated in at least two (and as many as five) altitude training courses during the study period. Did those who benefited once consistently benefit again? Here are the individual results for those 15 athletes, with upward bars indicating an increase in total haemoglobin and downward bars indicating a decrease:

(Illustration: Scandinavian Journal of Medicine and Science in Sports)

Four of the athletes (on the left) always benefited, and two of them (on the right) always saw neutral or negative reactions. For the other nine, it was a mishmash. Subject F1 had two good placements, then a bad one; subject F2 had two terrible ones, then a great one. The hard conclusion here, Nummela and his colleagues write, is that height response is not a fixed property.

The more difficult question then is: what determines whether you get a successful internship? A solid finding was that the success rate rose to 65 per cent when the altitude was at least 2000 metres. It turns out that the authors of this article were the ones who advised the Finnish national team on their altitude training, and they cannot help but point out that this is exactly what they originally told the national team coaches to expect. But did the coaches listen to their altitude training destinations? Apparently not always.

The physiologists also had two other pieces of advice for coaches: don't allow your athletes to reach high altitude if they have low iron levels (defined as serum ferritin below 30 micrograms per litre) or if they are sick (as indicated by levels of the inflammatory marker C-reactive protein above three milligrams per litre). These rules were not enforced either, so the researchers checked whether people with low iron levels or high inflammation were less likely to respond. The results were inconclusive: the non-responders had slightly higher baseline ferritin and lower C-reactive protein than the responders.

In contrast, other studies have shown that having good iron levels and avoiding illness are crucial to achieving good results from altitude training. And the physiologists who work closely with elite athletes have plenty of other ideas about what it takes to ensure a successful training block in thin air. The real conclusion, again, is that getting the most out of altitude training is complicated and highly individual. You can take that as a half-empty glass: simply booking a plane ticket doesn't guarantee anything. Or you can see it as a half-full glass: even if your first high-altitude internship didn't work out, you might still be able to make it work next time - if you understand the details correctly.


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