By Martyn Herman RIO DE JANEIRO, Aug 16 (Reuters) - As Britain's track cyclists left Rio's velodrome on Tuesday with their saddle bags laden with gold, their rivals were left scratching their heads wondering just how they managed to keep peaking at the Olympics. "Of course we are wondering," Germany's Kristina Vogel, who did stem Britain's charge by winning the women's sprint, told reporters on the final day of a memorable track programme. "It seems they do nothing for three years, then they start at the Olympics and kill us." Yet there had been question marks over Britain's dominance of the boards this year. More...