This is one of those funky looking exercises that works your back and rear shoulder muscles more than you think it would.
A lot of it is to do with the smaller back and shoulder muscles never fully getting to rest so there is a lot of tension working through them.
The bodyweight version is pretty easy to master so from here hold light dumbbells or weight plates in each hand.
• Lay face down on a low incline box or step with legs straight and abs and butt muscles braced tightly
• Start with lifting the hands to the side of body in line with low chest / sternum with elbows pointing up towards the ceiling as much as possible
• Hands should not touch the floor during the exercise
• Breathe out and extend the arms directly out to the side of the body
• Continue until the arms are fully extended and body is in a "T" shape.
• Breathe in and pull the hands back to the start position whilst squeezing the elbows back in
This is my, mostly, Personal Trainer musings and information which I hope you'll find helpful!