American runner Mary Cain has shared allegations of systemic abuse during her time at a high-profile Nike training group, prompting an investigation by the sportswear giant.

Key points: Mary Cain joined the Nike Oregon Project as a 17-year-old with aspirations of being the "best female athlete in the world"

Mary Cain joined the Nike Oregon Project as a 17-year-old with aspirations of being the "best female athlete in the world" But she says the psychological abuse she suffered led her to begin cutting herself and contemplating suicide

But she says the psychological abuse she suffered led her to begin cutting herself and contemplating suicide Nike says it will investigate these "deeply troubling" claims, but says Cain tried to rejoin the program in April and didn't raise concerns then

Cain joined the disbanded Nike Oregon Project, run by disgraced American middle-distance coach Alberto Salazar, in 2013, soon after competing in the 1,500 metres final at track and field's world championships when she was 17.

At that time, she was considered one of the brightest prospects in world track and field, and had already set multiple national records.

In a New York Times video essay, Cain said at the time she had designs on becoming "the best female athlete ever", and joined the Oregon Project to make it happen.

But, now 23, Cain said she was instead "emotionally and physically abused by a system designed by Alberto and endorsed by Nike", to the point where she had suicidal thoughts and began cutting herself.

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Cain alleged that under Salazar's direction, she was told to lose weight and he created an "arbitrary number of 114 pounds (51.7kg)".

"He would usually weigh me in front of my teammates and publicly shame me if I wasn't hitting weight," she said.

In 2015, Cain said after a race she told Salazar and the team's sports psychologist she was cutting herself and they "pretty much told me they wanted to go to bed. I think for me that was my kick in the head, where I was like, 'This is a sick system'."

Mary Cain joined Alberto Salazar's program in 2013 after making the world 1,500m final. ( AP: Don Ryan )

Nike said in a statement these are "deeply troubling allegations which have not been raised by Mary or her parents before. Mary was seeking to rejoin the Oregon Project and Alberto's team as recently as April of this year and had not raised these concerns as part of that process".

The sportswear giant says it will "take the allegations extremely seriously and will launch an immediate investigation to hear from former Oregon Project athletes".

Coach banned for supplements experiments

Salazar was last month banned from the sport for four years by the US Anti-Doping Agency for experiments with supplements and testosterone that were bankrolled and supported by Nike, along with possessing and trafficking testosterone. Nike shut down Salazar's elite program.

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In addition, Nike said last month that longtime chief executive Mark Parker would leave early next year.

Cain said "young girls' bodies are being ruined by an emotionally and physically abusive system. That's what needs to change".

In trying to cut weight, Cain said she didn't have her period for three years and broke five different bones. Cain also said Salazar wanted to give her "birth control pills and diuretics to lose weight", the latter of which isn't allowed in track and field.

"I ran terrible during this time," she added in the video.

"It reached a point where I was on the starting line, and I'd lost the race before I started because in my head all I was thinking of was not the time I was trying to hit but the number on the scale I saw earlier that day."

Cain's story has drawn overwhelming support from the running community.

Shalane Flanagan, who holds the US records in the 3000m, 5000m and 15-kilometre road race. reached out to her on Twitter, posting: "I had no idea it was this bad. I'm so sorry (Mary) that I never reached out to you when I saw you struggling. I made excuses to myself as to why I should mind my own business. We let you down. I will never turn my head again."

Cain responded to Flanagan by posting: "I can't express how much this meant to me. It was scary to feel so forgotten by a community I devoted my life to. But together we can change things. As athletes, it's easy to hand our agency to others, but new coaches can change the system".

At the end of her seven-minute video, Cain said she plans to keep running.

"I genuinely do have hope for the sport and I plan to be running for many years to come. Part of the reasons why I'm doing this now is I want to end this chapter and I want to start a new one," she said.

ABC/AP