Hot & Dry vs Hot & Humid

Hello Kenny:

I would have to say that I think it probably does take more energy to stay
cool at higher humidities than it does at lower humidities with all other
factors the same. When the humidity is high the perspiration will not
evaporate as readily to cool the body. Therefore the body might actually be
warmer in the high humidity.

In the dry conditions the perspiration evaporates easily and helps cool the
skin better. This may lead to closer to normal body temperatures.

Just make certain that whether you are in high humidity or low that you
drink enough fluids to keep hydrated.

Here in the area that I live a warm summer ride is in the 90's for both the
humidity and the temperature. It would be really nice to try riding where
the humidity was a little more moderate.

Al Butler

Quoted message said:

energy at the end of the rides. Does high humidity impact the body's
performance more that dry conditions at the same temperature?

Absolutely! The key, in either high or low humidity, is to keep yourself
hydrated. I started my XC MTB ride in the 94 degree Florida heat at noon
after drinking about 1/2 gallon of water... I had forgotten my Camelbak and
I didn't have a jersey or a bottle cage to hold a bottle. 2 hours later, I
was fine!

--
Phil, Squid-in-Training

ZeeExSixAre said:

Quoted message said:

energy at the end of the rides. Does high humidity impact the body's
performance more that dry conditions at the same temperature?

Absolutely! The key, in either high or low humidity, is to keep yourself
hydrated....

That is only half of what is needed. Water intake without salt to
replenish what is lost through perspiration can lead to hyponatremia.
Hyponatremia is one of the more unpleasant things one can experience.

--
Tom Sherman – Quad City Area

Kenny Lee said:

Lately the weather has been hot and very humid. 36c with 90+ humidity.
On this weekend's club rides I've felt like a wet rag in need of
disposal. I think it's the humidity that's zapping my strength. When I
do these same rides in normal dry weather conditions I have a lot more
energy at the end of the rides. Does high humidity impact the body's
performance more that dry conditions at the same temperature?

Yes.

See this chart:

http://www.crh.noaa.gov/pub/heat.htm
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Surrealism is a pectinated ranzel.

Thanks all. Nice to know it's not all due to the aging process.

Kenny Lee

Tom Sherman said:

ZeeExSixAre said:

Quoted message said:

energy at the end of the rides. Does high humidity impact the body's
performance more that dry conditions at the same temperature?

Absolutely! The key, in either high or low humidity, is to keep
yourself hydrated....

That is only half of what is needed. Water intake without salt to
replenish what is lost through perspiration can lead to hyponatremia.
Hyponatremia is one of the more unpleasant things one can experience.

Can you describe it further?

I complemented the water with fruit juices (apple, cran, orange) and a
banana, BTW.

--
Phil, Squid-in-Training

Kenny Lee said:

Lately the weather has been hot and very humid. 36c with 90+ humidity.
On this weekend's club rides I've felt like a wet rag in need of
disposal. I think it's the humidity that's zapping my strength. When I
do these same rides in normal dry weather conditions I have a lot more
energy at the end of the rides. Does high humidity impact the body's
performance more that dry conditions at the same temperature?
Kenny Lee

High humidity also decreases the density of the air and wind resistance
is lower with increasing humidity.

When its hot and humid, the lower density comes at a measurable price
in partial pressure of oxygen. If its 90 F and 90% RH, even if you are
at mean sea level, the density altitude your body feels is more like
5000 feet. For aircraft, these conditions are like 3000 feet of
altitude but their engines can compensate for the lower partial
pressure of oxygen since the EGT's will be lower. But human lungs canot
compensate.

--

Water transfers heat far more efficiently than does dry air. This is why
high humidity makes a hot day feel like a sauna, and makes a cold day
feel absolutely frigid.

Because of this, the higher the humidity, the more you will *feel* the
heat on a hot day. The more you feel the heat, the more you will sweat
to compensate. The more you sweat, the more liquids you will need in a
given period of time to replace it.

Also, the more liquids you need in a given period of time, the more you
need to reduce the carbohydrate content of your sports drink to meter
the volume of carbs per hour.

--

"Kenny Lee" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Lately the weather has been hot and very humid. 36c with 90+ humidity.
On this weekend's club rides I've felt like a wet rag in need of
disposal. I think it's the humidity that's zapping my strength. When I
do these same rides in normal dry weather conditions I have a lot more
energy at the end of the rides. Does high humidity impact the body's
performance more that dry conditions at the same temperature?

Kenny Lee

When humidity is high, your body's cooling technique of sweat evaporation is
not as efficient. That is why you wind up covered in sweat - the uptake of
additional moisture in humid air is more difficult. Here in the Arizona
desert, we think nothing of riding in temperatures over 100F but then the
humidity is, at this time of year, often in the single digits. You sometimes
wonder if you're actually sweating because the sweat is evaporated so
quickly. Then you see the crusty salt deposits in your clothes and helmet.
Many homes and businesses in the southwest desert use "swamp coolers" for
cooling to save on electricity costs. These are simply large fans blowing
through wet pads; the outflowing air is cool (and moister). Weather
forecasts here typically also include a guide for whether your swamp cooler
will work well or not. I think the dew point has to be below about 55F for
them to have much cooling capacity.

Quoted message said:

Here in the area that I live a warm summer ride is in the 90's for both the
humidity and the temperature.

While the above is often stated it is practically impossible to have 90+
humidity at the daily high temperature assuming normal temperature variation
between day and night. If the nighttime low temperature is for example 68F
with a 100% humidity then assuming no weather change a daily high temperature of
98.6F gives a humidity of 39%.

See http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/watvap.html#c1

Ted B said:

Water transfers heat far more efficiently than does dry air. This is why
high humidity makes a hot day feel like a sauna, and makes a cold day
feel absolutely frigid.

That's not why humid air feels hotter. It's because rates of
evaporation are lower in high humidity, or zero at 100% humidity.
You continue to sweat, but there is no evaporative cooling.

The thermal conductivity of dry air is 50 times greater than that of
water vapor.
--
terry morse Palo Alto, CA http://bike.terrymorse.com/

"Ian S" wrote: (clip)You sometimes wonder if you're actually sweating
because the sweat is evaporated so quickly. Then you see the crusty salt
deposits in your clothes and helmet. (clip)
^^^^^^^^^^^
Another clue is that you don't pee.

Weisse Luft said:

Kenny Lee said:

Lately the weather has been hot and very humid. 36c with 90+ humidity.
On this weekend's club rides I've felt like a wet rag in need of
disposal. I think it's the humidity that's zapping my strength. When I
do these same rides in normal dry weather conditions I have a lot more
energy at the end of the rides. Does high humidity impact the body's
performance more that dry conditions at the same temperature?
Kenny Lee

High humidity also decreases the density of the air and wind resistance
is lower with increasing humidity.

When its hot and humid, the lower density comes at a measurable price
in partial pressure of oxygen. If its 90 F and 90% RH, even if you are
at mean sea level, the density altitude your body feels is more like
5000 feet. For aircraft, these conditions are like 3000 feet of
altitude but their engines can compensate for the lower partial
pressure of oxygen since the EGT's will be lower. But human lungs canot
compensate.

In the portion of the lung where gas exchange occurs, the air is always at
98.6F and 100% RH. In other words, the partial pressure of water is always
47mmHg inside the lung, regardless of what the weather is like outside.

ZeeExSixAre said:

Tom Sherman said:

ZeeExSixAre said:

>energy at the end of the rides. Does high humidity impact the body's
>performance more that dry conditions at the same temperature?

Absolutely! The key, in either high or low humidity, is to keep
yourself hydrated....

That is only half of what is needed. Water intake without salt to
replenish what is lost through perspiration can lead to hyponatremia.
Hyponatremia is one of the more unpleasant things one can experience.

Can you describe it further?

I complemented the water with fruit juices (apple, cran, orange) and a
banana, BTW.

In my case I drank a lot of water at a rest stop on a 90+ F, 90%+
relative humidity day. About one-half hour later I started suffering
from a severe headache and general disorientation. It was the one time
that I have sagged in on a ride, since I had enough mental function left
to know it would be really stupid to "prove" that I could tough out the
discomfort (especially after reading about all the athletes who die from
heat related illness).

--
Tom Sherman – Quad City Area

Jim Smith said:

In the portion of the lung where gas exchange occurs, the air is always at
98.6F and 100% RH. In other words, the partial pressure of water is always
47mmHg inside the lung, regardless of what the weather is like outside.

Good point, but since total pressure changes with altitude, so does
the partial pressure of water vapor.
--
terry morse Palo Alto, CA http://bike.terrymorse.com/

Tom Sherman said:

In my case I drank a lot of water at a rest stop on a 90+ F, 90%+
relative humidity day. About one-half hour later I started suffering
from a severe headache and general disorientation.

No matter how hot it is, don't drink more than about 24 oz. of water
per hour. But if you do end up drinking more than that, be sure to
take on extra electrolytes (which is a good idea on a hot day, any
way). Hyponatremia is not a good thing to have. Stop immediately if
you feel lightheaded or queasy or get the dry chills.

Dehydration is far less dangerous than hyponatremia.

Pouring water over yourself on a hot ride will help cool you down,
but drinking extra water won't help and may be really bad for you.
--
terry morse Palo Alto, CA http://bike.terrymorse.com/

Terry Morse said:

Jim Smith said:

In the portion of the lung where gas exchange occurs, the air is always at
98.6F and 100% RH. In other words, the partial pressure of water is always
47mmHg inside the lung, regardless of what the weather is like outside.

Good point, but since total pressure changes with altitude, so does
the partial pressure of water vapor.

Actually, no. Because the air is saturated with water vapor in the alveoli where
gas exchange occurs, the partial pressure of water is equal to the vapor pressure
of water, which is dependent only on temperature. Inside the lung the partial
pressure of water is always 47mmHg. It makes no difference what the partial
pressures of the other gases present are. As altitude increases and total
pressure goes down, that 47mmHg does, of course, become a larger percentage of
the total. At sea level, for example, the fraction of water vapor is 47/760 =
0.062 or about 6%, while at the summit of Mount Everest the fraction is about
47/205 = 0.229 or 23% of the total.

Terry Morse said:

Tom Sherman said:

In my case I drank a lot of water at a rest stop on a 90+ F, 90%+
relative humidity day. About one-half hour later I started suffering
from a severe headache and general disorientation.

No matter how hot it is, don't drink more than about 24 oz. of water
per hour. But if you do end up drinking more than that, be sure to
take on extra electrolytes (which is a good idea on a hot day, any
way). Hyponatremia is not a good thing to have. Stop immediately if
you feel lightheaded or queasy or get the dry chills.

I may have experienced that. I got light-headed, but only when I stopped
riding for 20 seconds or so (I usually ride a brisk pace and am terribly out
of breath when I stop) Does this sound like hyponamentirenaeieia?

Other than sports drinks, what are some good, compact, cheap sources of
electrolytes?

--
Phil, Squid-in-Training

Ed said:

Quoted message said:

Here in the area that I live a warm summer ride is in the 90's for both the
humidity and the temperature.

While the above is often stated it is practically impossible to have 90+
humidity at the daily high temperature assuming normal temperature variation
between day and night. If the nighttime low temperature is for example 68F
with a 100% humidity then assuming no weather change a daily high temperature of
98.6F gives a humidity of 39%.

See http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/watvap.html#c1

Not this old canard again. Is there some reason the physicists who
put this [censored] up prevent water from evaporating when the temperature
rises above 68F? Is there some reason the nighttime low will always
be 68F or below?

Or is this the old, "Assume a spherical cow" gone to meteorology?
Email address works as is.