Grab a dumbbell with both hands and lay on a flat bench.
Extend your arms so the dumbbell is overhead for your starting position. You want your palms to be underneath one of the sides of the dumbbell.
With a slight bend in the arms, move the weight behind your head in a semicircular motion until the DB is behind your head, parallel with the floor. You should feel a strong stretch in the Chest and Lat.
In the same movement plane, pull the dumbbell back to starting position.
Don’t let the dumbbell go further than your head when pulling it back up.
The arms do not initiate the movement. They are levers for your lats and chest.