double up

I'm going to double up my enlistment.

"It is well, then that we should be frank," said the other. "We both think more than we have said; let us make a clean breast. This masked figure that you saw, did you recognise it?" / "Well, sir, it went so quick, and the creature was so doubled up, that I could hardly swear to that," was the answer. "But if you mean, was it Mr. Hyde?--why, yes, I think it was!"

This unfolding sofa doubles up as a bed.

Jones snared the liner and then stepped on the bag to double up the runner.

Tactically smart, Leeds' work-rate was also admirable, their players often doubling up on Everton's main threats like Marouane Fellaini, while Victor Anichibe found he had unwelcome, unstinting company throughout.