Lady Gaga sweats it out in 100-degree yoga session

Lady Gaga got hot and sweaty as she showed off her moves during a gruelling Bikram yoga session.

The Poker Face star turned up unexpectedly at Tricia Donegan's Manhattan studio – where she posed for pictures and left 39-year-old Donegan a thank-you note.

Bikram yoga practitioners brave temperatures of up to 100 degrees as they work out.

At first, Donegan said she didn't recognise the 24-year-old singer, real name Stefani Germanotta, who used to attend her yoga classes when she was a student at New York University.

'Gaga said to me, 'To jog your memory, I confided in you and cried in your lap about a food problem I was having,’' Donegan told a local news station.

'She told me I had talked to her about the proper hydration and proper nutrition necessary to having enough energy and strength.

'She said she no longer has a food problem and that I saved her life.'

Asked if the pop star was any good at yoga, Donegan said: 'I don’t know if she’s flaming hot, but she’s definitely hot.'

She also revealed that Gaga’s thank-you note, scrawled on pink paper, read: 'Tricia, Thank you so much for today. Lately, I've been kicking a** in yoga, but I'm excited to embark on an even deeper journey with you. You are such an inspiration. I will be back soon. With more hydration + sleep.

'Yoga heals me + so do you. Love, Lady Gaga.'