High Altitude and Acclimatisation Part 1 - An Introduction

In the first of our four-part series on high altitude travel, Jamie Macdonald (high altitude physiologist at Bangor University) and Calum Muskett (professional climber and mountaineering instructor), explore the role of physical fitness in mountaineering success.


To be (fit), or not to be (fit), that is the question...

With Comic Relief 2019 just behind us, cast your minds back to Sport Relief 2009. That year's challenge also required nine celebrities to leave their comfortable television and music studios to climb to 5895m and attain the highest point on the African continent - Kilimanjaro. Hardened mountaineers were easy to dismiss the stunt as another guided charity trek on a non-technical peak, with porters doing all the hard work, made worse by the paraphernalia of the following TV crews. Fast and light it was not. But mountaineers and the masses alike were surprised to see that of all the celebrities struggling for breath on their TV screens, the beer swilling, pie eating, cigarette smoking, belly-sporting Chris Moyles seemed happiest in the rarefied air. And he summited successfully.

The classic Cosmiques Arête in the Mont Blanc Massif.  © Calum Muskett
The classic Cosmiques Arête in the Mont Blanc Massif.
© Calum Muskett

The success of Moyles is often quoted when the role of fitness for high altitude performance is debated. Invariably 'two ciggies' Don Whillans gets a mention too, and then personal experiences are regaled with glee of seeing young fit athletes doing poorly at altitude in comparison to their older, unfit counterparts. Unfortunately, all these anecdotal examples provide weak scientific evidence, and if we are brutally honest, are often quoted to justify a lack of personal preparation for the reciter's current or next adventure. But getting expedition-fit requires considerable time, effort and resources. So, what scientific data and applied best practice exists to help you prepare for altitude exposure?

First, we need to separate two factors – altitude illness and altitude performance. Surprisingly they are not as linked as you might imagine. Mountaineers are a (fool?)hardy bunch – mild and moderate acute mountain sickness (an altitude illness) often does not stop us from achieving our goals such as summitting (an altitude performance). Rightly or wrongly we tend to stoically push on through mild and moderate symptoms such as headache. So, let's deal with performance first, and altitude illness later.

In mainstream sports such as cycling, a common scientific approach is to study elite athletes and describe their characteristics. Such classical studies have also been completed in mountaineering on Reinhold Messner and colleagues. Following physiological testing, scientists were surprised that Messner was not super fit – his aerobic capacity (VO2 max, a measure of endurance fitness), was high (49ml/kg/min) but not extremely so (Tour de France cyclists are often more than 75ml/kg/min). Many have argued that this evidence suggests being fit is not helpful for altitude performance. However, this interpretation is over-simplistic.

Ally Swinton in the Monte Rosa.  © Calum Muskett
Ally Swinton in the Monte Rosa.
© Calum Muskett

Unlike mainstream sports such as cycling, numbers participating in mountaineering remain relatively small. Thus, there is little opportunity for characteristics and traits to become 'common' in elite mountaineers. In mass participation sports, there are multiple opportunities for competitive selection to occur and only the very best rise to the top. Take a sample of elite cyclists at the peak of their careers, the top few athletes in a pool of millions worldwide who cycle regularly for pleasure and competition, and you will observe common characteristics that explain their performance, such as high aerobic capacity. In mountaineering, competitive selection opportunities are few and far between. Take a sample of elite mountaineers, and the characteristics displayed will be disparate and inconsistent. Opportunity and psychology, rather than genetic factors, explain participation and success.

Messner, Whillans, and Moyles summitted their respective peaks partly because they had the chance to; not necessarily because they were genetically gifted to do so. This point also raises the tantalising prospect that sitting out there in the general population are other people who will be better suited to mountaineering and potentially "elite", but they have not had the chance to even try a pair of boots on.

Although this might explain why elite mountaineers are not super fit, and why unfit people have succeeded in mountaineering, why is it that we observe fit people "doing poorly" at altitude? It is especially important to separate illness and performance here. In terms of performance, we know that for every 1000m you climb, your aerobic capacity (VO2 max, a measure of endurance fitness) decreases by about 8% [see box 1]. This decrease in endurance fitness reduces performance. There is some evidence that reveals the fittest participants experience a greater decrease in aerobic capacity when at altitude. Some argue that this evidence 'proves' that being fit is not helpful for altitude performance. Again, this interpretation is over-simplistic. Although a fitter person may experience a greater percentage decrement in their aerobic capacity, their absolute aerobic capacity at sea level and when at altitude remains higher than a less fit person. Thus, a fitter person will have greater exercise capacity and fitness reserve for when speed is important (e.g. to avoid benightment or incoming weather).

Reduction in aerobic capacity (VO2 max, a measure of endurance fitness) with increasing altitude.  © UKC Articles
Reduction in aerobic capacity (VO2 max, a measure of endurance fitness) with increasing altitude.

Admittedly, scientific data is difficult to obtain in mountaineering because 'performance' is hard to measure. Summit success is perhaps the ultimate measure of mountaineering performance, but it will be influenced by other factors such as weather and partner failure. Mountaineering performance is hard to measure in the lab too – mountaineering activities typically last for hours or days – which is impossible to simulate and replicate. In any case, summit success and speed may not be every mountaineer's most important goal. Therefore, we took an alternative approach and studied sense of effort (how hard typical mountaineering exercise feels, sometimes referred to as Rating of Perceived Exertion) as a measure of performance. Sense of effort is a good measure of performance because sense of effort controls walking speed (the key determinant of whether a summit is successfully reached) and because it influences enjoyment (when exercise feels too hard it is not enjoyable).

In a group of typical trekkers and mountaineers, we observed that the fittest had lower sense of effort during simulated and actual mountaineering tasks. When speed was restricted (such as when walking with others tied into a rope together), the exercise felt easier and was thus more enjoyable. When speed was not restricted, the fittest could also select ascent rates that were quicker, increasing chance of summit success. So, if Moyles was fitter he might have enjoyed his climb more; if Messner had been fitter he may have even more summits at first attempt to his name.

But what about those cases we have all seen, of fit people getting sick? The physiological causes of altitude illness are only just being determined [see diagram below]. Recent lab studies by our group and others on the cause of acute mountain sickness suggests a mechanism that is not influenced in any conceivable way by fitness. Later studies by our group tested this theory in the field and showed that being fit did not increase risk of the most common altitude illness – acute mountain sickness. It is most likely that Moyles didn't get sick on Kilimanjaro because his skull was big enough to accommodate his brain as it swelled at altitude, not because being unfit protected him somehow.

Diagram 2  © UKC Articles
Diagram 2

There have been some observations suggesting that the fittest may be at increased risk of severe altitude illnesses, such as pulmonary oedema. However, these observations are difficult to interpret because ascent rate was not controlled (the fittest participants likely gained more altitude and completed more arduous exercise each day, and thus were at increased risk of illness regardless of their fitness level). We would argue that being fit may even protect against high altitude deaths. A study on Everest revealed that the most common symptom reported before death was fatigue – and being fitter is well established to reduce fatigue symptoms.

In summary, current evidence suggests that whether you are fit or unfit, you can get sick at altitude. However, being fit will increase your chance of summit success and your enjoyment. Nevertheless, the strongest evidence to put this argument to bed once and for all is yet to be generated – what happens when you increase fitness of a group of mountaineers, and compare their mountaineering performance to a group whose fitness has stayed the same? Perhaps a great study for the UKC community to participate in!

With all this talk of fitness, an obvious strategy that we could all use is to increase fitness before we travel to high altitude. Of course, this is not simple, requiring time, a little guidance or knowledge, and most importantly, motivation. However, the advantage of such a strategy is that it requires no specialist equipment, no altitude chambers, no hypoxic tents, and no lengthened altitude stays. It is thus accessible to all of us. Just be mindful of the double-edged nature of this approach. Being fit is advantageous, but if you exercise too strenuously (and ascend too rapidly) when at altitude, you will increase your risk of illness. Be fit, but move slowly until fully acclimatised.

In the next article in our series, we will discuss the acclimatisation process and explore classical and best practice acclimatisation profiles.

About the authors:
Dr Jamie Macdonald is a high-altitude physiologist and the head of the School of Sport, Health and Exercise Science at Bangor University. A keen mountaineer, Jamie has climbed extensively in the European Alps and taken his altitude research to the Himalayas.
Calum Muskett is a professional climber and mountaineering instructor who splits his time between the mountains of Snowdonia and the French Alps.


This post has been read 7,026 times

Return to Latest Articles or view other Hill Skills


24 Apr

The Messner stat is interesting... I've also seen that he claimed to do the vertical k in 35 minutes. With a vo2 of 49 you'd expect a vertical k time of an hour or a bit more i.e. a VAM of 900m-1000m (rough estimate based on my concurrent 5k / vertical performance and estimates of vo2 that come from 5k times). Even if he did it in 40 minutes that would be a VAM of 1500m, well in excess of what you'd expect from vo2 and at that sort of intensity (80-85% vo2 max) vo2 max has a reasonable impact (vs a mountaineering type performance where efficiency, performance at LT1 is perhaps more important). Someone like Kilian Jornet who does the vertical K in 30-31 minutes has a world class vo2 so can't imagine that Messner, in peak shape, would have had one as low as 49! Probably didn't have a world class vo2, as I don't think vo2 is one of the top 3 predictors of mountaineering performance, but just as a factor of being that fit I'd expect something significantly higher. Maybe they tested him when he wasn't so fit or when he was more focused on rock climbing?

24 Apr

Nice article. I remember reading the original 1986 JAP article on Messner a while back, and being quite taken aback at his apparent physiological normality. The great Peter Wagner offered an interesting take on the findings, suggesting in 2017 that: "High muscle capillarity, enhancing diffusive unloading of O2, may have been a major enabling physiological attribute for Habeler and Messner."

https://www.physiology.org/doi/pdf/10.1152/japplphysiol.00140.2017

25 Apr

...being fit did not increase risk of the most common altitude illness – acute mountain sickness. It is most likely that Moyles didn't get sick on Kilimanjaro because his skull was big enough to accommodate his brain as it swelled at altitude,...

I realise this is only Part 1, but I see a large and illogical leap between these two sentences, with no evidence for the latter. It just introduces a whole new factor with no background. Given the range of physiological factors that affect acclimatisation, it seems odd to simply put Moyles' state down to a big skull, and, that will only reduce headache, not stop him getting 'sick'. Or is this just poor editing?

Sense of effort is a good measure of performance

Really? Both personal experience and quite a bit of reading contradict that. I think it can affect performance, but not 'measure' it. 'Sense' of effort is very subjective, and there is no mention here of the 'central governor' factor where psychological factors override physical properties. Thresholds of pain and perception of effort vary between people. It is such psychological factors that were offered for the success of Messner (and Kukuczka) in the absence of their quantitatively 'poor' test results.

26 Apr

Presumably the argument about skull size relates to volume within the skull not already occupied by brain. If one has a big skull and a big brain occupying all of it, there's no space to allow the brain to swell. If the brain is small in relation to skull volume, there's space to allow the brain to expand without causing symptoms. If so, one would expect older climbers to do have fewer symptoms in the early stages of acclimatisation than younger ones (and children and adolescents might be expected to struggle). Is this supported by the evidence?