Ok I’ll put my two cents worth in. It doesn’t sound like you were dehydrated, usually with dehydration your pulse rate goes down. It sounds more like you were overheated, the pulse rate went up trying to cool you down. How much training in the heat had you done before you did this ride? I have found, from living in Bakersfield, Ca, that it take me about three weeks of training in the heat before I’m fully acclimated to the heat. The sweat glands have tiny muscles around them and if they aren’t use to working that hard and long they tire and quit squeezing to pump sweat out to help cool you. Therefore the body increases the HR trying to get more blood to flow pass the surface trying to cool it self.
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Make mine a double!