Why is he working out his upper body, he needs to work on his lower body strength.
Defencemen generally need a stronger/bigger upper body for more frequent one on one and front of net battles, especially a Juulsen type of D man who's considered more of a "stay at home" defenceman.
If there's anything you should trust from a professional sports orga organization in 2018, it's the training program they provide. Each player has a program designed for them. The concern isn't the program, it's whether the young up and commer is disciplined enough to follow it.