If you’re coming to this British comedy as a fan of carrot-topped Simon Pegg (Hot Fuzz, Shaun of the Dead), be advised that his collaborators this time aren’t writer-director Edgar Wright and roly-poly sidekick Nick Frost but American TV vets David Schwimmer (who directed) and Michael Ian Black (who shares script credit with the star). Five years after ditching Thandie Newton at the altar, a chubby Pegg finds her with overachieving fitness buff Hank Azaria and contrives to win her back by completing the London marathon. This feeble premise limits the movie to perfunctory gags about the hero’s sloth and some canned underdog drama. Dylan Moran has a few funny moments as Pegg’s shiftless pal and Mike Leigh regular Ruth Sheen puts in an all-too-brief appearance. PG-13, 100 min.