Sunday, October 03, 2010

Hitting the Wall: Rethinking Altitude Sensitivity

I went yesterday doing an experimental day hike to Mt. Hoffman in Yosemite and pretty much everything I was assuming about altitude is wrong and this is very good news.

I went over to Yosemite to do a day hike of Mt Hoffman which is 10,850'.

In the past

I would hike until 7200' or 9600' and suddenly all the excess energy or oxgen (wasn't sure what) in my muscles would fizzle away. I could feel the it just dissipate or drain away with me going "wait, come back!" The 7200' limit I consistently hit on Shasta when I hiked up from Bunny Flat and also on Ralston Peak. The 9600' happens also on Shasta after spending a night at Horse Camp and it's also happened on Lassen (though Lassen seemed to happen more around 9000'.)

So I had some elaborate theory about there must be some change in the air pressure at that level. This is how you get all sorts of weirdo, crackpot theories and superstitions. You think you are seeing something consistently, but in fact you are managing to cause it in some other way.

Recently I've been working on a problem with my running. My foot would drag after 1 mile which was somewhat heat related, but the biggest factor was working too hard and letting my heart rate go up to 90% bpm which is not maintainable. Cutting it back to 85% of my max bpm made a huge difference and then I could go much further without a leg drag.

So I thought it was worth trying this out at altitude. My plan for today saw to attempt to climb Mt Hoffman (10,850') from the May Lake trailhead (8800'), but wear a heart rate monitor and keep my heart rate at 85%. I also took Diamox and Aspirin to increase my chances of success.

It short it WORKED!! I summitted and had energy to spare, and all my altitude theories are totally wrong.

So what has been happening is that my heart has been working too hard while climbing and my heart is not pumping enough oxygen to keep things going and I run out of energy which in cycling circles is called "bonking." It's worse at higher altitudes because the lower air pressure makes the oxygen harder to come by. I'm an endorphine junkie and I love working hard when exercising and the feel of my heart beating and being able to keep going hard.

I had to stop a lot to keep my heart rate down as especially at altitude it always wanted to climb over 85%. It makes for slow climbing and while I'm almost always never jealous of 20-somthings, their heart rates can work much harder without working anaerobically, and they can go racing by me. Hmphf. In theory, over time, they can run into the same problem and do on real mountains like Shasta.

What's cool about this is that I can work on my fitness level at sea-level and that will no doubt help and it much easier to obtain.

My original plan was to spend the night and do the climb again to see if there was a difference if I had adapted more to the elevation, but that's not necessary.

So what was happening? Why the consistency in elevation?
I think it was just a fabulous coincidence. That moment happened when I "hit the wall" and it turned out to be about the same amount of time that my heart rate was working too hard. In Shasta it happened more than twice, but I was leaving from the same location and working just as hard.

This is so fantastic as it means that the world has opened back up to me. I know I can now summit Whitney. Shasta is another issue as you have to be able to climb it within a certain amount of time. I'll work on my fitness level over the Winter and see if I can make a difference in the amount of time I can run before my heart rate climbs above 85% when either running above 4.0 mph or at some incline.

I might also try my Black Friday (day after Thanksgiving) snowshoe of Mt Shasta, but if I'm able to climb higher there could be an avalanche issue and I might be better off going over to Hidden Valley and up towards Shastina. Or just make things simpler and go to Lassen Park and Brokeoff Mtn which is right at the park entrance (the road through Lassen is closed in Winter.)


At first I thought what I was running into was called Oxygen Dept, but it's sounding more like:

Hitting the wall (Glycogen depletion)

What's interesting about this is:

Athletes engaged in exercise over a long period of time produce energy via two mechanisms, both facilitated by oxygen:

How much energy comes from either source depends on the intensity of the exercise. During intense exercise that approaches one's VO2 max, most of the energy comes from glycogen.

So with low oxygen glycogen production is conpromised.

A little more info here

An excellent description of the exercise process is here:

Oxygen debt which I first thought I was dealing with is the term as it's more referring to the process when the body is at rest.

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