Over the past several years, I have kept detailed records on morning body weight as well as notes on my reactions and adaptation to altitude, and have arrived at some remarkably consistent findings (e.g., no exceptions, ever).
When I travel to high altitude (10,000' - 12,000'), the following occur:
- The first 8-30 hours, I urinate like crazy, so much so that the first night I am up 5 or 6 times to empty my bladder. This always happens and I always lose 2-3 pounds of body weight, yet I am not dehydrated (clear urine, ample fluid intake).
- At 24-36 hours, a marked improvement in aerobic ability occurs at high altitude.
- At 36+ hours, the fluid-shedding behavior ceases and things return to normal. But if body weight was 172 prior, it is now 169.5 (or so): a loss of 2-3 pounds.
- At 7-9 days, another bounce in aerobic capacity (this one has to do with maturation of additional red blood cells).
These things ALWAYS happen when I go to altitude, meaning every one of the ten or so trips I’ve made to altitude in the past 2.5 years. No exceptions.
What does this mean for a high-altitude race like the Everest Challenge? At the very least, arriving the day before is a very bad idea, two days being an absolute minimum, and camping at least at 9,000' to adapt. Nine days is ideal, which is why I make it a point to schedule a photography trip prior to EC.
What might be going on
My understanding is that somewhere in the first 24 hours of going from sea level to 11,000' elevation, the body dumps its “standby” reserves of spare red blood cells in the spleen into the bloodstream as an adaptive measure. In short, natural blood doping by using altitude!
The proof is in the performance 24-36 hours later: hugely better. And the initial “brain fade at 13,000'” disappears. Ergo, an increase in hematocrit. Also, my power meter is totally objective. And I pay close attention to how I’m performing on the bike, from long attention and practice of self-awareness. The effects are consistent and dramatic, every time.
Back to the fluid observation: my guess is that in order to “make room” for those red blood cells, the body needs to shed fluid for whatever new plasma balance is appropriate.
Since I adapt very quickly to altitude (a fact known from long experience), my guess is that my body is pretty darn good at dumping a large number of fresh red blood cells into the bloodstream, raising the hematocrit and dramatically increasing my aerobic ability at altitude. And that to do so, it has to shed fluid, a lot of it.
The graph below shows two marked dips just prior to the 2011 and 2012 Everest Challenge events: both show a sudden loss of body weight of 2-3 pounds corresponding to the pre-race acclimatization: this is not reduced eating or a sudden starvation diet: it is fluid loss plain and simple, observed and measured.
Note that after the Everest Challenge I return home to near sea level, and body weight bounces right back up. And my shoes become too tight! The body is now adjusting by adding all that fluid right back in. Happens every time, like clockwork.