I agree with what others say, it's the humidity as much as the heat that makes it so tough to exercise when it gets hot. Admittedly here in the(usually) cool UK high temps are rare. Last week did a ride in around 85F which for where I live is hot but it was the humidity which was tougher. Somewhere like Aus where it's dry heat not so bad imo. For what it's worth I love the hot weather, time to move if I can persuade the family!