CLEVELAND -- Sit up and don't slouch.

Troubleshooter Chris Caswell found out for this week's Betcha Didn't Know that there is a 90-degree rule when sitting at a desk.

"Your ankles will be at 90 degrees, and your knees will be at 90 degrees, and when your hands are positioned properly, your elbows will be at 90 degrees," University Hospitals' Occupational Therapist David Edelstein said.

A head bent for the phone, reaching for a computer mouse far away from your keyboard and using a footrest are all mistakes that can take a toll.

Edelstein said whether working on the computer, driving a car, or working at a work bench, we wind up with our shoulders internally rotated, heads forward and our upper backs curved.

Caswell said that it's important to take a break to get up and stretch while at work.

"It's important to get up at least once an hour, and to stretch and get into a position that is opposite of the way you had been sitting," Edelstein said.

He added that buying a chair should be like buying a pair of shoes: Fit matters.