Weak shoulders

[NotAGolf]

A while back (2 years ish) I got tendonitis in my shoulder so I had to stop training at them gym, ever since then I've only ever done shoulder exercises with dubmbells (shoulder presses, front raises and lateral raises). I tried doing military presses on the smith machine the other day and i'm unbelievably weak, it hurts slightly accross my left collarbone, its the same with shoulder press machines, and a little bit with a barbell inclined bench press.

To give you some idea of my weakness, I can shoulder press about 50kgs with dumbells but only around 30kgs on a smith machine/barbell. It seems to be any machine where I'm restricted movement wise.

Is there any way I can strengthen these set of muscles across the collarbone area or is likely to be some other problem that I should get help with?

Thanks

 

[NotAGolf]

But surely it shouldn't be hurting so much on the collarbone area, more on the actual shoulder? I know they're all linked together but it's pretty intense.

 

[NotAGolf]

Yea that's 25kg in each hand. Ok thanks for the advice will be staying away from the smith machine!

I must admit that I do bend my back a bit when I'm working shoulders. I have the back-rest up and tend to arch my back a bit, but it's worse when I'm standing or sitting with a backrest. I just find it very hard to keep a good posture, if I get my back dead straight then my shoulder movement becomes much more restricted. Is this normal or have I just got a god awful posture in general so have got used to it?