After thinking about all of the above - I have one question about core body temp. Checking what it is should be easy with oral thermometer. With a little searching I find that exercise can raise core temp by several degrees with 104 being the upper limit. Any ideas on what kind of increase should one aim for? Gee wonder who will be first to market cycling computer with body temp and sensor. Seems to me that would be more valuable in knowing when to back off or stop than heart rate info.