Energy Expenditure at Altitude - Not really the hypoxia
Posted: Wed Apr 28, 2010 5:00 am
After getting into the estimation of calories burned while hiking, someone brought up the fact that I didn't consider the altitude. Well I looked up a review research article and wrote up and interpreted what it said.
Basically they found that cold temperatures were the cause for increased basal metabolic rate at altitude, not hypoxia (although needs many more studies). They also stated that actual work performed at altitude (like hiking / climbing) does not itself need more calories than at sea level. However, the increased intensity due to lower O2 pressure -> burning more glycogen -> eat more carbs.
This was just one review article. Anyone got some other sources?
Posted: Wed Apr 28, 2010 5:26 am
I have no reliable sources, only personal experience - which is a common problem, as you say in the article. There is little true control and a lot of very unreliable anecdotal 'evidence'. It's even worse in the field of AMS, HAPE, HACE etc as the consequences of ignorance and misunderstanding can be so much worse.
I think your 2nd last and 3rd last paragraphs are pertinent. Decreased appetite leads to a greatly reduced intake of calories - of any type - and this is the prime factor in weight loss. There is nothing magic about altitude burning up your muscles - it's just you eating less and working pretty hard. It's the flip-side of the obesity problem. People don't realise just how easy it is to ingest calories in the normal urban world. Carry and cook those calories yourself in an expedition setting and things change. I see this all the time with polar expeditions. Skiing to either pole is usually said to burn up around 8,000 calories a day. It's almost impossible to eat this much - especially if you don't have McDonalds, KFC and Pizza Hut nearby - using normal 'camping' foods. So most polar expeditioners lose weight - I lost around 16kg / 35lbs in 60 days over 700 miles. I say 'most' as not everybody experiences this and there are severable variables in the mix - genetics, diet, starting weight, tactics, logistics, terrain etc.
Some people find that they are actually less active on mountaineering expeditions, as there is so much sitting around waiting for weather and acclimatising. Type-A fitness freaks often find this very hard to handle. A lot of climbing expeditions don't actually involve much climbing.
Another factor to consider is the assumption of cold at altitude. Whilst this may be the case in North America, extremely high temps can still be found up to and around 6000m (20,000ft), especially in the Karakoram. On several occasions I have experienced measured temps of around 30-35C at 5500m and thereabouts, and that was on glaciated terrain.
Posted: Wed Apr 28, 2010 11:52 pm
thanks for the input. that's a lot of weight loss!
I guess there's a way to conquer the obesity epidemic...
Posted: Thu Apr 29, 2010 12:32 am
I typically lose a pound a day on climbs like Denali and Aconcagua but that's because I just can't eat that many calories on a climb. Good thing I can easily put on an extra 10-12 pounds of extra fat between climbs to get me though.