Biometeorology! A nice post confirming the science of what many sufferers of the conditions you list have always suspected--frequent changes in barometric pressure can bring pain (although this is *not* yet universally accepted in the medical community).
I'd just like to touch on a couple of things, though, Rob. I'm sure you didn't literally mean that the body comes under "less gravitational force" when the air pressure drops. Gravity (as distinct from an object's attractive force, which is "gravitation") is a constant force, and is independent of air pressure. Air pressure is a function of mass per unit volume, as with any gas occupying a space. Pressure falls and rises, as we know, due to lifting and subsidence with cyclones and anticyclones, respectively. The synovial fluids that bathe our joints seem to react to the drop in absolute pressure; pain results when those fluids fall slightly "out of balance" with the pressure and compensate by expanding (inflammation), thus irritating achy joints.
So actually, athletes and those with chronic pain do sense the change in the "weight" of the air, with that weight being, (as for all mass on earth), gravity (a constant force) times the mass of the air surrounding the body and its fluids, which *does* change w/changing pressure. So when the barometric pressure is low, it's literally *less* weight our joints feel, rather than *extra* weight. On top of this, everything depends on the strength of the particular low pressure cylcone or trough in question.
Also, the central tissue of our vertebral discs, or the "nucleus pulposus," is not water; it's actually more of a jellylike substance. If it were water....I'd imagine the reaction to lower pressure would be....*ouch*...exCRUCiating!! :)
As for the desert southwest and SoCal for training, I'm honestly not 100% sure, but I would posit that it's the climate being far more constant, or persistent, (i.e. hot surface and upper air heat ridges for more of the time throughout the year) than it is over most of the rest of the nation.
Rob..thanks for posting entries on such a wide array meteorological topics. There's so much more than just the daily forecast!
How are we going to have a record warm fall when september is much cooler and october will likely remain the same? With the negative NAO in place still, i would expect a wetter and cooler fall and going into el nino our storms will be coming from the south and thats how we get our snowstorms in the winter in the mid atlantic. How cold do you think it will be by November? NOAA always has above normal temps in the forecast, so i dont put much faith into their outlooks.