MJ's Movie "This is It": Is That Him or a Body Double?

Knowing Michael's weak state at the time "This Is It" and all of his rehearsals, there are reports that the producers were using body doubles and audio tapes to make the King of Pop look healthier. At the time of filming, it was reported that MJ couldn't even hardly walk, and that his voice was shot. But magically in the film, he looks strong and his voice sounds better than ever. I hope its really him, but I'm starting to doubt it after hearing this.