Originally Posted by
Bontrager
When it's rediculously hot out your body is trying to get rid of the excess heat by dialiating vessels under your skin. When it does that, with all otehr things being equal, your heart gets less blood to pump. REceptors in your heart, kidneys, carotid arteries, etc tell your heart they want more blood (volume) so your heart beats faster.
Perfect!! ...and good on you debunking the oxygen theory with regards to temp and oxygen density.
Additionally, if the OP is feeling a loss of power then that is simply electrolyte depletion. ECaps dude. Pack some ECaps and drink water. I recommend this over sport drinks. Read on:
Why? Because when it's super hot (especially at higher elevation where the atmosphere is thinner and the sun's rays are especially brutal) you can dump water from your water bottle over your head. This is a super effective way to help your heart out with that cooling function that the wise Bontrager explained to you.
Besides, sport drinks make a mess of your frame, legs, wheels ...you get the idea.