By Martyn Herman RIO DE JANEIRO, Aug 18 (Reuters) - Even when he landed with a fearful crack on the unforgiving concrete of Rio's BMX track and realised his bike was in pieces, Dutchman Niek Kimmann's race was not run. Unperturbed, the 20-year-old grabbed his mangled frame and hobbled around the second half of the course, reaching the finish line well over a minute after the winner before collapsing and being surrounded by medics. More...