My biology book says if you stand still on a hot day for a long time you're more likely to faint.
The standing still part I gather, is due to the leg muscles not squeezing the veins to force the blood upwards towards the heart. But I wonder why the hot day part.
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Anonymous2012-05-21 5:11
You feint due to low blood pressure, on hot days you sweat more and so are more likely to be dehydrated and dehydration lowers blood pressure.
Your blood will be all over your extremetries so your core will not be as bloody on a hot day.
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Anonymous2012-06-08 11:53
Maybe it's because your body heat will increase the heat of the air around you. If you move, you'll be surrounded by cooler air that hasn't absorbed your heat (even on hot days, the temperature rarely goes above your body temp). But if you stay still, you're surrounded by the hot air.
Of course, a breeze or fan will solve this. But this is just a possibility.
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Anonymous2012-06-09 18:51
Being warm reduces the core blood pressure, this is why you feel faint in hot baths
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Anonymous2012-06-23 23:56
Yes, the blood pressure lowers due to the body dilating arterioles of the skin in order to radiate heat. The result is less blood to the brain, causing light-headedness and fainting.