training Ninja with Sandy Zimmerman

Sandy Zimmerman was the first MOM to complete the American Ninja Warrior obstacle course.

Click PLAY or watch it on YouTube.

She trains and coaches in her backyard in Spokane, Washington. Her husband and 3 children all compete.

I observed one open class last night — and got a chance to try the warped wall myself.

Sandy Zimmerman, a full-time teacher, is an excellent coach.

Mary Lou Retton to DWTS?

A source tells ET that Olympian Mary Lou Retton is joining the cast.

“She turned 50 this year, but is in great shape and will definitely impress people with her flexibility and choreography,” the source says of the former gymnast, who won a gold medal in the individual all-around competition as well as two silver medals and two bronze medals at the 1984 summer games in Los Angeles. …