put one's back into it
Make a strenuous effort, as in If you put your back into that report, you'll soon be done. This idiom alludes to physical labor involving the strength of one's back. It was first recorded in 1882.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.