Justin Timberlake hangs "upside down" to hype himself up before shows.
The 'Take Back the Night' hitmaker is said to have a set "routine" backstage before his gigs, which includes two hours meditation and a ban on "talking".
Speaking to The Sun on Sunday newspaper, an insider said: "Justin is really strict about routine before his gigs.
"He believes keeping talking to a minimum and meditating gets him 'in the zone'.
"The hanging upside down bit gets his heart rate going as last-minute preparation."
However, Justin is still spontaneous - earlier this month he brought fan Josh Clemons on stage so he could propose to his girlfriend Kim Martin.
He brought them onstage, telling Kim: "Josh called me earlier. He's got something he wants to tell you."
The singer then exited as Josh got down on one knee and made his proposal, which Kim accepted, sending the 22,000-strong crowd wild with cheers of congratulation.
Justin then returned, bringing the happy couple shots and leading fans in a toast.
He said: "This is for Josh and Kim. Louisville is for lovers, baby!"