I saw a skinny guy all in black collapse on a climb during a long event ride I was on. He was even wearing long sleeves. Before he dropped, he was riding sitting up, with his arms held out to catch the tiny breeze. Good bike handler. It was about 104° according to my Garmin. I was in yellow with white sunsleeves and not having any trouble other than it was hard work climbing 7% on our tandem with 100 miles already in our legs. The aid car was busy that day.