We are currently experiencing a heatwave in the southern part of the UK, temp up in 90's, and so far have not noticed a difference in my performance on the bike. Plenty of water with an isotonic additive seems to keep me hydrated, but I do not appear to sweat a great deal until I stop at the end of the ride. I suppose it could be the amount of liquid I take in, or the cycle specific clothing, or (Tongue in cheek this) the speed I go at keeps me constanly in a draft.
In the garden I wilt. I am dead- no energy to keep the garden tidy, no enthusiam to do the jobs that should be done, until it cools down in the evening. So- why is it that I can go out for 3 or 4 hours exercise and not feel the heat anymore than I would do on a winters day.