Rosa Khutor (Russia) (AFP) - Two competitors in the women's Olympic snowboard cross event at the Sochi Games were stretchered off after crashing badly in Sunday morning's seeding races.
Medal hopeful Helene Olafsen from Norway -- the first snowboarder on the course -- was taken to hospital with a knee injury.
The other casualty in the seeding run -- where riders compete alone against the clock for a better seeding for the afternoon quarter-finals -- was American Jacqueline Hernandez.
Later on Sunday, two skiers needed treatment after crashing on the aerials and halfpipe slopes during training.
Swiss aerials competitor Christopher Lambert suffered a suspected dislocated elbow while Britain's Rowan Cheshire was stretchered off the halfpipe after being knocked unconscious.
Many athletes have described the cross course as fast, forcing them to control their speed on certain sections rather than just go hell for leather all the way down.
It was the second time in three days Olafsen, who finished third at last year's world championships and fourth at the 2010 Vancouver Games, had crashed.
She was also carried off on a stretcher on Friday after cutting her forehead in a fall.
"She's being taken to the local hospital with a knee injury and she will not compete," a Norwegian team spokesman said.
Hernandez appeared to hit her head after falling awkwardly and was also stretchered off, although she was conscious at that point.
She was also unable to take part in the second seeding run for the event, won by Eva Samkova of the Czech Republic.
The end of the snowboard cross course uses part of the slopestyle piste, which was heavily criticised earlier in the Games after a series of crashes.
However, the snowboard cross crashes happened further up the course before it merges onto the slopestyle track.
By the time the freestyle skiers took to the slopestyle course, a few days after the snowboarders, many were describing it as perfect.
Lambert, whose older brother Thomas also qualified for the Sochi aerials competition, crashed heavily on his right arm during training.
He was treated by medical staff on the course before being taken to hospital, meaning he is almost certain to miss Monday's competition.
Cheshire fell heavily on her face and was unconscious for several minutes before being stretchered off the pipe and taken to a nearby medical tent.
Her event is not until Friday but there is no indication yet whether she will be able to recover in time.
Previously, during snowboard training on the slopestyle course, another Norwegian, medal hope Torstein Horgmo, broke his collarbone in a fall while in the women's freestyle skiing training American Heidi Kloser broke her thighbone and tore her cruciate knee ligament after crashing.
Russian freestyle skier Maria Komissarova, who fractured her spine in the worst accident of the Winter Olympics, has been flown to the German city of Munich for further treatment, her federation announced on Sunday.