Re: Rattlesnake Ridge ride - heat and humidity! (kind of long)

[Ramey Peticolas-Stroud <ramey@wvi.com>]

Steph Teeter wrote:
 
> Always something new to learn. And it looks like I'm going to have to
> get serious about heat management. Body clipping, conditioning
> during the heat of the day ... all that big black horse stuff.
> 
> Any advice or tips are welcome!
> 
> Steph


Hi Steph,

Any discussion of heat management would necessarily address muscle mass,
skin color, level of fitness, etc. etc.  I'll leave those topics to
others and discuss a thermo-dynamic concept called "latent heat of
evaporation."  You don't hear much about it in endurance but it's
surprisingly important.

The heat generated by muscular action can be dissapated in a number of
ways, but a major process is for blood to be shunted to surface
capillaries for cooling.  For example, the capillary modeling we see on
fit horses is nature's way of increasing surface area to enhance
air-heat exchange (same principle as a car's radiator).  

Water (sweat or sponging) on the horses skin absorbs a certain number a
calories or BTU's (measures of thermal energy) when under going the
transition from a liquid to a gas.  This is where the real cooling
action occurs.

In a high humitity situation, the liquid-vapor transition point is
elevated because it is pressure-dependent.  In other words, in high
humitity water vaporizes at a higher temperature due to increased
atmospheric pressure (this is why a car has a pressurized raditor cap). 
Thus the ability of sweat or sponge water to vaporize and absorb heat is
dramatically reduced in high humitity conditions.

The folks in the East have learned this lesson well and they sponge or
spray their horses constantly, almost at every road crossing.  They have
learned that in high humity, "conductive cooling" is much more effective
than "evaporative cooling."

I have also seen crews in the East apply ice water the horses under
stress, then let it sit for a few seconds and then scrape it off-- then
they do it again and again.  I'm not sure how they keep from causing
muscle cramps, but maybe someone from the East will jump in and explain
the process.

One last thought.  The XL Performance equine temperature monitors are
really interesting.  They cost about $170 but provide insight that is
not normally available.  For example, yesterday was a moderate heat/high
humity day here at the CEC.  Three of our horses did interval work on
the same course, at the same pace, carrying the same weight.  Although
heart rates were comparable, working surface temps varied: 99.5 - 102.1
- 103.2.  Why the variations exist is beyond the scope of this post, but
I do know that the data will cause us to manage these horse differently
under similar high humidity conditions.

Happy trails and cool, dry air...

Ramey and Cynthia Peticolas-Stroud
Cascade Endurance Center
Lyons, Oregon