All force in the upper body travels through your back. Even if you’re doing push ups and hand stands, the work you want your pushing muscles to perform needs to travel through your back in some way.
This is why keeping your back tight and stable is very important in every upper body exercise you do including grip and arm work.
Try this as a warm up before your next workout:
Hang from either a pull up bar or in a row position. Do you best to forcefully contract all of the muscles in your back and the pulling chain including your biceps, forearms and especially the back of your shoulders. Now try to get that same tension to be present in all of your upper body work to some degree.