Police are questioning a couple after a bruised and half-naked 17-year-old boy showed up at a gym Monday with a chain locked to his ankle, claiming he had just fled his captors, authorities said.

Matt Robinson, a spokesman for Tracy police, said authorities believe the teen was held against his will in Tracy _ a city about 60 miles east of San Francisco _ after he ran away from a Sacramento foster home in 2007.

Robinson said authorities are questioning a couple in their 30s, but that they have not been arrested or charged.

He said the emaciated boy was confused when first approached by detectives, unsure where he had come from and how long he was being held against his will.

"The wounds he had and his physical condition as well as having a chain around his leg corroborated his basic statement that he was being held against his will," Robinson said.

Chuck Ellis, a manager of the In-Shape Sports Club in Tracy, said the boy came into the fitness center Monday afternoon wearing only boxer briefs, covered with what appeared to be soot. Ellis says the teen was scared someone was going to come after him and asked to be hidden.

"He said, `Don't let them get me, don't let them get me,'" Ellis said. "He was totally terrified."

Ellis said the teenager told him he was picked up after running away from the foster home to look for his family and that he was held for almost a year. Ellis said he looked like he was between 10 and 12 years old.