there are a few ways, i used to live in eugene oregon, and when i came down to race wildflower i got killled by the heat, took it out of me. You can sit in a sauna stationary and sweat it out. You can turn up the heat in your house and ride the trainer, or you can put on layers of clothes (sweat suit) and ride the trainer indoors. Be very careful about the sweat suit, drink plenty of liquids etc and stop if you feel dizzy. Out of the options i posted, the sauna is the least effective. I've done a lot of research on the bodies reaction to heat, and the body responds mch better to training in heat than sitting in it. Also, the higher your ability to operate near your V02 max the better your ability to cope with heat. IE the more fit you are the better off you will be.
I've heard that if you wear dark clothes your skin temp will be higher but your core temp will be lower, dont ask me how. Shave the hair off your body come race time.
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Vintage Cervelo: A Resource