Definition of «to arch the back»

"To arch the back" means to bend or curve the spine outward, creating a shape that is concave in the front and convex in the back.

It may seem like no matter what you do, your child is fussy or irritable or arches his back during feedings. (verywellfamily.com)
For example when a cat arches its back, is it upset or is it friendly? (petpeoplesplace.com)
Don't roll your back or over arch your back either. (liftingrevolution.com)
(see all sentences)