Pulling this across from the bladder/bottle down your top discussion/thead. @bja1016 said:
. . . putting a cold bottle/bladder in your kit in Kona will actually cause an increase in your core body temperature, so that would have the opposite affect if you're trying to keep cool. And vice versa, a warm bottle/bladder on a cold race will cause a drop to your core body temperature. Watch this:
[And later from @bja1016:] Video at 18:45 to about 25:30 and then @1:47:52. To summarize this, humans are endothermic, which means we use thermoregulation to maintain the body's internal core temperature. The brain controls thermoregulation, in the hypothalamus specifically. For an analogy, if you're in a sauna that's 190 degrees and you put cold water on the thermostat, it's going to heat up the room, because the temperature was artificially decreased. The body works in a similar fashion, and our thermostat is in the hypothalamus, not on our skin. The skin has receptors which sends signals to the brain to rise or lower core temperature. So if you put a cold bottle or bladder on your kit, those receptors on your skin will register the cold against the skin and send a signal to your hypothalamus to increase internal core temperature.
There are three areas on your skin (glabrous skin surfaces) where this doesn't apply: palms of your hands, bottom of your feet and the top half of your face. So if you're trying to keep cool in a hot race (Kona), you'd be better off wearing a cooling glove than applying a cold towel or bladder to your chest, back or neck.
I know this sounds completely counter-intuitive, @bja1016 said
. . . putting a cold bottle/bladder in your kit in Kona will actually cause an increase in your core body temperature, so that would have the opposite affect if you're trying to keep cool. And vice versa, a warm bottle/bladder on a cold race will cause a drop to your core body temperature. Watch this:
[And later from @bja1016:] Video at 18:45 to about 25:30 and then @1:47:52. To summarize this, humans are endothermic, which means we use thermoregulation to maintain the body's internal core temperature. The brain controls thermoregulation, in the hypothalamus specifically. For an analogy, if you're in a sauna that's 190 degrees and you put cold water on the thermostat, it's going to heat up the room, because the temperature was artificially decreased. The body works in a similar fashion, and our thermostat is in the hypothalamus, not on our skin. The skin has receptors which sends signals to the brain to rise or lower core temperature. So if you put a cold bottle or bladder on your kit, those receptors on your skin will register the cold against the skin and send a signal to your hypothalamus to increase internal core temperature.
There are three areas on your skin (glabrous skin surfaces) where this doesn't apply: palms of your hands, bottom of your feet and the top half of your face. So if you're trying to keep cool in a hot race (Kona), you'd be better off wearing a cooling glove than applying a cold towel or bladder to your chest, back or neck.
I know this sounds completely counter-intuitive, @bja1016 said