Damon, 42, spent an hour on the weights on Saturday and returned the next day with Clooney, 52, and their bodyguards – much to the delight of regulars.
Liane Shadrack, 42, manager of the Kelsey Kerridge Sports Centre, in Cambridge, said: “Members found it a bit distracting and maybe didn’t work out to their full potential.”
The pair are shooting war film The Monuments Men in nearby Duxford, written, produced and directed by Clooney.
It’s based on the book Monuments Men: Allied Heroes, Nazi Thieves and the Greatest Treasure Hunt in History by Robert M. Edsel.
Matt plays James Rorimer – the former director of the Metropolitan Museum Of Art in New York – who packs it in to join the US Army.
George plays George Stout, and the impressive cast also includes Cate Blanchett, Bill Murray, Hugh Bonneville and John Goodman.