stiffen up

stiffen something up

to make something rigid or tense. He added a little starch to the rinse water to stiffen his collars up a bit. The cold draft has stiffened up my neck.
See also: up

stiffen up

to become stiff. The bread dough stiffened up as it got cold. My knees began to stiffen up after I sat still for an hour.
See also: up
References in periodicals archive ?
If he comes through that okay and doesn't stiffen up on Wednesday there's a great possibility he'll run on Friday.
He's still sore, but the biggest thing is that his knee didn't stiffen up.
It won't have that feeling if you let him write the answers, because chief executives tend to stiffen up when they write.
I started to really stiffen up and could not walk," he explains.
It's definitely not as cold and the swimmers don't stiffen up as much,'' Lounder said.
Dafoe was concerned that the charley horse he suffered in a morning practice before Tuesday's game against the Phoenix Coyotes might stiffen up, but he felt no side effects Wednesday.