Katie that sounds terrible. I find that I am really affected by the heat too. One thing my husband taught me one year when we were putting a roof on our house during the summertime. He gave me a few grains of rock salt and told me to put them under my tongue. I guess this is a trick roofers use (he used to be one).
Whenever I feel that heat headache coming on, I will do that, and it really helps.
I don't blame you for not wanting to excercise in that sort of heat, I do most of my excercise early in the morning, but I know it isn't easy for everyone.
I'm talking small steps here, so you can choose what small changes you want to make. If it isn't a good idea for anyone, then that is fine, we don't have to do it, I just thought it would help us reach our goals.
