First, don't be concerned - you won't actually dislocate your shoulders here. Shoulder dislocations are perfectly safe if you do them correctly, even if you had a dislocated shoulder before. Just don't rush it and be persistent. This exercise will be challenging initially, but you'll quickly improve if you're consistent at it.
You'll need a broomstick for shoulder dislocations although I recommend you get a mini-band as I'll explain below. Video of me doing Shoulder Dislocations:
How to do Shoulder Dislocations Correctly. NEVER use the barbell for shoulder dislocations - it's too heavy, you could injure yourself. Just grab the broomstick wide, reach over until you hit your back/hips, and then come back. Repeat for 3 sets of 10 reps as warm-up for your Squats/Bench/Press. Quick technique tips:
- Start Wide. If you can't do shoulder dislocations without your elbows bending or your hands leaving the stick then your grip is too narrow for your current flexibility level. Grip the stick wider, as wide as possible.
- Use a Resistance Band. Iron woody Bands makes shoulder dislocations a lot easier if you lack flexibility because the band stretches as you reach overhead. Get a mini-band if you struggle with the broomstick.
- Be Persistent. You will obviously not eliminate bad posture caused by years of computer games or too much sitting overnight. But your posture and flexibility will quickly improve if you're persistent. So be patient.
If you have very bad posture and lack shoulder flexibility, I recommend you also do the next exercises to improve your flexibility and fix your posture:
- Doorway pec stretches – stretch your pecs
- Thoracic Extension on roller – eliminates hunchback posture