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Extreme heat ops, conditioning, adrenalin & kidneys

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Saw something truly remarkable on FSN's Sport Science the other day that bears directly on a number of CMSF issues. Basically, the desire was to quantify the effects of dehydration on athletic performance, in a properly supervised but highly demanding scientific test series.

An American rugby star was first put through a series of rugby related drills to establish his baseline and warm him up. He was then put in a rubber exercise suit, placed under searing lights and ran for an hour on a treadmill, during which he sweated out no less than 14 lbs. of water weight and was very close to the 105 degree heat stroke core temperature range. He then clambered out of the exercise suit and ran the same rugby course as before. He not only did as well as before, but he shaved two seconds from his earlier time. How was this possible?

The commentary said that this was the result of not just adrenalin's kicking in, but of the super efficient kidneys possessed by the rugby player. His, you see, worked 30% better than typical ones, thus keeping blood thin longer, in turn reducing the load on his heart. The principal mechanism of dehydration is that the kidneys, lacking adequate moisture content in the blood as someone progressively dehydrates, can't keep up with the buildup of impurities, leading to ever thicker blood and ever greater load on the heart, which must beat more rapidly to move the same blood volume as before.

The player tested had played before on 110 degree days and found it rough, but had never been subjected to anything like what he went through in the test, a test so grueling it, per the the commentary, would've killed the average person not in such great physical condition. I think this test neatly illustrates the value of physical conditioning in enduring thermal extremes, but also shows how some of the amazing feats we read of in military accounts are possible. If you get a chance to catch the episode, it's well worth your time.


John Kettler

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