Density Altitude and human performance

G-Man

G-Man

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I live in Colorado, about 5,500' MSL. Today was hot and dry, about 95F. Density Altitude was above 9,000', maybe 9,200 or so.

We watched a Piper Cherokee PA-28-140 takeoff with a mighty shallow climb angle, two on board. This led to me trying to explain Density Altitude to a non-pilot friend.

He asked: How does this affect people? Is it just like being at higher altitude when climbing a mountain?

Good question! I know there's less lift, and engines have less oxygen (but that matters less). But what about human performance? Is it the equivalent of hiking or being, in this case, at 9,200' MSL?

I should know this, but I don't. What sayeth the gurus of POA?
Thanks.
 
Humans are very much affected by altitude.
I used to hike a lot, and climbing a mountain at 10,000' is a lot harder than it is at 2,000'.
 
Probably the biggest difference is that humans can acclimate to some degree.
 
Salty said:
Why not?
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It's a semantics thing, but he's not wrong.

This is because our net ability to associate oxygen from inhaled air into the blood within the lung membranes, is a function of the differential pressure between the inhaled gas fractions (so called partial pressures) and that of the same gases in the blood. That's the mechanism of exchange, the mechanical pressure differential.

Here's where people get confused. Density altitude is just a non-standard temperature adjustment for the pressure altitude reading. So let's tackle what differentiates the two: temperature. In the association of oxygen in the hemoglobin, the control temperature is that of blood temperature, not OAT. Us being hot-blooded and all, the temperature at the exchange is effectively constant. Thence, density is normalized for; it plays no role in this exchange. Pressure (partial pressure to be precise), and therefore pressure altitude, is the relevant metric.
 
Humidity as well as temperature affects density altitude correct? Isn’t humid air less dense because some air molecules are displaced by water - so wouldn’t that cause a corresponding effect on human performance, since each breath of air would have less “air” in it? If there was some impact it must be very small, as I cannot recall humidity causing the sort on impact on physical exertion that higher altitude does.
 
I think the effect of humidity on density altitude is small compared to the effect of temperature, so it should hardly matter.

I’ll admit, on humid days, my human performance is in the toilet, but that’s for different reasons.
 
Good discussion. A flat lander who finds himself /herself at a hot and humid airport isn't going to be as sharp as someone who is acclimated. The next day in Denver is rougher for me than the first day, slight headache, etc. Through in heat and humidity and not going to be up to normal speed.
 
my location: down the road from G-Man.

Frankly, when DA (or temps) get too high, I'm not happy being outside, not to mention in an airplane. I prefer my basement, where it's nice and cool.
 
caverjamie said:
Humidity as well as temperature affects density altitude correct? Isn’t humid air less dense because some air molecules are displaced by water - so wouldn’t that cause a corresponding effect on human performance, since each breath of air would have less “air” in it? If there was some impact it must be very small, as I cannot recall humidity causing the sort on impact on physical exertion that higher altitude does.
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Once you breathe air, your body quickly saturates the air from moisture in your resp tract, and then gives the air a partial pressure of water of 47 mm Hg, that is consistent regardless of outside humidity. Temperature is likewise controlled by your body and the air becomes roughly 37 C. Your body is affected by barometric pressure which is the only part of the DA formula that applies to us.
 
Thanks, everyone! This is a more complicated question than I thought. Glad it's not something easy I should know, and appreciative of the helpful and informative posts.
 
I learned all about altitude when I was younger. I grew up at sea level. We were visiting family in Colorado Springs during a vacation, and I decided to go for a run. I think I made it to the front of the next door neighbor's house. Might be why the US Olympic training center is located there.
 
I think some are missing the distinction of altitude vs density altitude. I haven't seen anyone say anything that disputes that altitude matters.
 
High density altitude equals less pressure. Therefore your body thinks it’s at a higher elevation.
 
As stated above, high density altitude is function of temperature and humidity, your body is affected only altitude since the temperature and humidity is the same at the alveoli. Thus FARs regarding oxygen does not consider density altitude.
 
If the air is less dense, your body is affected by it, as is your airplane. If it bothers your planes take off and climb performance, it bothers us as humans to. I live at approximately 2,630' asl, and the air density at my home changes day to day, yet my home remains at the same elevation. That is know as density altitude, and affects horses, cattle, humans, planes, cars, dogs, and more.
 
midwestpa24 said:
Might be why the US Olympic training center is located there.
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And even there, they do things like sleep in reduced pressure rooms. To cause the body to make more red bloods cells to carry more O2 to the cells.
 
midwestpa24 said:
I learned all about altitude when I was younger. I grew up at sea level. We were visiting family in Colorado Springs during a vacation, and I decided to go for a run. I think I made it to the front of the next door neighbor's house. Might be why the US Olympic training center is located there.
Click to expand...
Seem’s I remember reading something about that once. It was about ‘live high, train low.’ Ya get acclimated to being high. Yer body adjusts to it. But it don’t help when trying to build muscle mass. Muscle got no brain. It just knows how much work it’s doing. More resistance, more muscle built. So ya’s gotta get back down to simply be able to put more stress on the muscle. So, after ‘living high’ for awhile, they goes into like pressure chambers or maybe just put on cannolis/masks, which gives a lotta oxygen to allow ya to lift heavier. Lifting heavier is what builds muscle.
 
I went running yesterday, it was 96 degree heat index. I’m pretty sure it was the density altitude that was killin me... just sayin... wow!
 
Hmm. So it’s like hottern’ a oars azz on payday outside. But you’re inside with the air conditioner on. Or vice versa. Cold outside but you’re inside with the heater on. Does the density of the air you’re breathing inside change?
 
The density of the air as it is inhaled is less. But by the time it gets to the lungs, the only determining factor is the pressure.
 
Yes, altitude can affect humans, that's why there's altitude sickness. Humans can adapt to high altitude over time through compensatory changes to the pulmonary and vascular system.
 
For human performance, it's all about pO2, the partial pressure of oxygen. This is essentially tied to pressure altitude, where pO2 is about 20% of total pressure. Unlike aircraft flight performance, which will linearly follow pressure altitude, human performance changes will be nonlinear due to the nonlinear binding curve of hemoglobin. Human performance (oxygen transport and utilization) is also affected by other factors such as how long you have been at altitude. Modifiers of hemoglobin oxygen transport accumulate in the blood cells of those who stay at altitude for more than a few weeks. Anyone who hikes at high altitude (and lives at low altitude) will readily recognize this effect above 5-10 thousand feet or so.
 
Well ya... don’t need to get into that here.
 
luvflyin said:
Seem’s I remember reading something about that once. It was about ‘live high, train low.’ Ya get acclimated to being high. Yer body adjusts to it. But it don’t help when trying to build muscle mass. Muscle got no brain. It just knows how much work it’s doing. More resistance, more muscle built. So ya’s gotta get back down to simply be able to put more stress on the muscle. So, after ‘living high’ for awhile, they goes into like pressure chambers or maybe just put on cannolis/masks, which gives a lotta oxygen to allow ya to lift heavier. Lifting heavier is what builds muscle.
Click to expand...

Training at altitude allows adaptation to lower O2 pressure, which involves the gradual accumulation of 2,3-bisphosphoglycerate in red blood cells. It takes several weeks for this to start happening. 2-3-bisphosphoglycerate increases the efficiency of oxygen delivery to tissues by modifying the oxygen binding curve of hemoglobin in an attempt to compensate for lower oxygen levels. When an athlete training at high altitude returns to lower, more oxygen-rich altitudes, they get not only increased oxygen loading of their hemoglobin from the higher concentration of oxygen, but retain the extra oxygen delivery efficiency conferred by 2,3-bisphosphoglycerate for a couple of weeks until it returns to normal levels. This will temporarily and significantly increase athletic performance.
 
Hmm, is there a way to artificially increase the 2,3-bisphoglycerate?
 
Pinecone said:
Hmm, is there a way to artificially increase the 2,3-bisphoglycerate?
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Not in any practical manner. There have been investigations of various dietary supplements to do this artificially, but they apparently do not work.
 
Bummer. Might help with asthma and COPD.

Is your avatar a Tiger?
 
chemgeek said:
Training at altitude allows adaptation to lower O2 pressure, which involves the gradual accumulation of 2,3-bisphosphoglycerate in red blood cells. It takes several weeks for this to start happening. 2-3-bisphosphoglycerate increases the efficiency of oxygen delivery to tissues by modifying the oxygen binding curve of hemoglobin in an attempt to compensate for lower oxygen levels. When an athlete training at high altitude returns to lower, more oxygen-rich altitudes, they get not only increased oxygen loading of their hemoglobin from the higher concentration of oxygen, but retain the extra oxygen delivery efficiency conferred by 2,3-bisphosphoglycerate for a couple of weeks until it returns to normal levels. This will temporarily and significantly increase athletic performance.
Click to expand...
How often/ long does the exposure need to be to gain the adaptation? I seem to be fairly unaffected by altitude, I wonder if that's just natural, or the fact that I spend at least an hour or two every week at altitude.

I understand sensitivity to altitude increases with age? I hope it doesn't go as fast as my eyesight is...
 
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