After a long workday at your desk or hours in a car, it’s normal to feel a little stiff. It may just be that your hip flexors and lower back are tight. But you could also be experiencing a potentially debilitating condition called gluteal amnesia, or dead butt syndrome.
“The name sounds silly, but the side effects are serious,” said Jane Konidis, a specialist in physical medicine and rehabilitation at the Mayo Clinic in Rochester, Minnesota.
https://www.yahoo.com/news/sitting-day-cause-dead-butt-121812958.html