(CNN) Denver police launched an investigation this week after a video from a high school cheerleading practice surfaced that the superintendent called "extremely distressing."

In the video, a teenage girl's face contorts in pain as she performs a split by extending her legs in opposite directions while sitting on the floor. An adult appears to be pushing her down and other girls hold her arms, apparently to prevent her from breaking out of the split. The girl cries, repeatedly asking them to "please stop."

The investigation of cheer practice at East High School will involve child abuse detectives, police said. Nobody has been charged.

None of them replied when CNN reached out to them for comment on Thursday.

Williams was quoted in the Denver Post as saying the video is being taken out of context.

"You can definitely say that what was in the video could be seen in a different light," Williams said. "I would love to tell my story, but I can't say anything else at this time."

In a news release, Superintendent Tom Boasberg said he became aware Wednesday of the "exercise used at cheer practices." Putting the employees on leave was standard policy and did not prejudge them, he said.

"I cannot state strongly enough -- as the superintendent of the school district and the father of two high school-aged daughters -- that the images and actions depicted are extremely distressing and absolutely contrary to our core values as a public school community," Boasberg said of the video.

Parents speak out

The video was shot at a June 6 practice, said Eric and Kirsten Wakefield, the parents of Ally Wakefield, 13, the student shown in the video.

Eric Wakefield said they liked Williams' disciplined coaching style at first but the intense practices -- sometimes seven days a week -- were tough for their daughter.

At the practice, Ally was forced to perform the split shown in the video, the parents said, though she was not flexible enough to do it on her own.

"That day was the first big physical activity practice -- this was probably within the first week or two of cheerleading," Eric Wakefield said. "The coach said 'We've got to limber you guys up.'"

"My daughter is begging them to stop," Kirsten Wakefield told CNN affiliate KMGH in describing the scene on the video. "It's not right."

Kirsten Wakefield, who says she's a former cheerleader, said the coach ordered other girls to do the split. If they didn't, they risked being cut from the team, she said.

Ally injured muscles and ligaments in her groin area, as well as her hamstring, according to her parents. Physical therapy was ordered twice a week, and her doctor told Ally to limit her activity, they said.

Even with her injuries, Ally went to cheer practice daily to support the squad and her friends, her father said.

Ally's parents said they met with Mendelsberg, the school principal, Williams and his two assistants early this summer to talk about how to proceed. Mendelsberg said the athletic department would assist with injury rehabilitation, the parents said.

Then everyone went away for summer break.

The school superintendent's statement did not address the meeting with the principal, and Mendelsberg and Williams did not return calls seeking comment on what was discussed.

When cheer practice resumed, other parents noticed the severity of the practices, the Wakefields said. Renewed complaints about the coach were brought to the East High administrators with no resolution, the Wakefields said.

A few days ago, Kirsten Wakefield shared the video showing Ally crying to a local media outlet, she said.

That's when the school system took action, the Wakefields said.

USA Cheer statement

The USA Cheer National Safety Council , a nonprofit that aims to increase interest in cheer and promote safety, said its officials had viewed the video.

"The American Association of Cheerleading Coaches and Administrators (AACCA) does not condone the coach's actions, and rejects them to the fullest extent," Executive Director Jim Lord said in a statement. "Stretching should never be taken to the level of causing pain. Of even more concern is failure to act when it is clear that a cheerleader is in extreme pain and begging to stop."

When asked if the group favors a particular method of teaching splits, Lord said by email: "While there are numerous ways for athletes to improve their splits, any stretching technique should include slow, methodical stretching over time to improve flexibility. In no way should any athlete, under any circumstances, be subjected to the apparent pain that we saw in this video."

"We know that in DPS and across the country, young athletes are pushed to perform their very best -- but challenging our students should never compromise their health and safety, or their personal consent. DPS does not and will not tolerate athletic or school cultures or practices that place our students in danger."

The superintendent's statement also emphasized student safety. "We absolutely prohibit any practices that place our students' physical and mental health in jeopardy," he said. "We do not and will not allow any situation in which a student is forced to perform an activity or exercise beyond the point at which they express their desire to stop."