He was dehydrated at the end of one stage and it undoubtedly cost him time. He hasn't coped with the oppressive heat in France this July as well as some of the other riders, and it may ultimately cost him the Tour.

I remember running a 5 km race once in high school under similar conditions. The weather had been relatively cool for two weeks during our training then shot up to 95 degrees F. on the race day. For some inexplicable reason my body adjusted much better than many other runners that day, and I finished in 4th place, which was a bit absurd to be honest. There were at least 10 runners clearly better than myself but who suffered dehydration or heat exhaustion and either dropped out or ran poorly and finished behind me. The weather can be a huge factor in endurance sporting events.