be as stiff as a board
1. to be very stiff It's so cold out there - the washing was as stiff as a board when I brought it in off the line.
2. if you are as stiff as a board, your body feels stiff and hurts when you try to move it, usually after a lot of physical exercise I cycled fifty miles yesterday and when I woke this morning I was as stiff as a board.
See Hard cheddar!, Hard cheese!, be as stiff as a ramrod