Europe captain Darren Clarke has allayed fears over the fitness of British Open champion Henrik Stenson ahead of next month's Ryder Cup defence at Hazeltine, Minnesota. Clarke, however, said on Friday that the world number four was simply being careful by withdrawing from the tournament. "
How is it possible for each generation of athletes to beat previous records and extend human physical capacity without doping? originally appeared on Quora - the knowledge sharing network where compelling questions are answered by people with unique insights. MORE FROM QUORA: What was the best moment
Ratings predictions for the weekend in sports TV, including the NFL preseason and an early start to the college football season.