This is a sign that is very characteristic of a disorder that appears in children. Good luck!
It is gowers sign. Gowers sign seen in muscular distrfophias (duschenne, becker) , polimiozitis P.S. I'm sorry for my english:)
Tripod sign or gower’s sign in duchene muscular dystrophy. Males are predominantly affected as it is X-linked and usually don’t survive after the age of 14-15.