The scenic backdrop on Tour of Qinghai Lake seems to almost taunt cyclists who realize the beauty comes at a price and can be, literally, breathtaking.

The tour challenges their physical limits with its tortuous 2,002-kilometer route an average altitude of 2,496 meters above sea level.

After finishing five stages of the 13-leg tour, elite riders know they have been tested. "It's a problem. Sometimes in a race like the Qinghai tour, you want to look around because the scenery is different (from other tours)," Ralf Matzka, from German team Netapp-Endura, said after finishing third in the fourth stage. "But your body reacts to the height very quickly as you feel the lack of oxygen. We have to concentrate on racing."

The golden flowers and a blue, shimmering lake must go by unappreciated by the cyclists. Rico Rogers, a New Zealand rider with Synergy Baku Cycling team, even hired a chauffeur to drive him around the mountains when he debuted at the tour in 2011.

"The scenery is stunning. That's the only word to describe it," said the 35-year-old. "I have some photos and I still think it's unbelievable when I look at them now."

However, the sixth stage on Friday will not seem so beautiful. Starting at 10 am from Xihai, a town on the northeast bank of the lake, riders have to climb over a 4,120 meter high mountain during the tour's highest 205-km stage before arriving Qilian County.

Riders, knowing the challenges they face, have tuned up their lungs and legs by taking hypoxia-simulating training in advance. "I have an altitude business, where you practice at altitude facilities in Melbourne. I used that a lot before coming here. I knew it's a hard, high race but it's good to be back," said Rogers.

Italian rider Mauro Finetto, who claimed the third-stage, attributed his performance to altitude training. "I trained two weeks before at a mountainous regon in Italy. It's only 2,200 meters but it's better than nothing."