What can I do to increase the range of movement in my shoulders (in any or all directions)?
Is it even possible to significantly increase the range of movement in young adulthood?
And what sorts of exercises and movements should I definitely avoid that will further restrict or "lock in" the shoulders' range of movement?
When you do military presses, the optimal way to activate the entire shoulder and even trapezius is to shrug when you're at the top of the movement.
So as you go up, you normally press the weight until your arms lock out. If you're familiar with the shrugging movement, you can do this one trick to really push your shoulders, by activating your traps with the shrug motion. Essentially when your arms are at the top, extend them maybe an inch further and pull your traps in. Guaranteed to build you up.
Also, consider internal and external rotations for shoulder mobility and warm-ups, this will help with your rotator cuffs during lateral and front raises.
Swimming is also a big one for shoulders. +1 @JohnP
Stay thirsty my friends
When I hear you say “lock in” that make me think of people who have had shoulder surgeries where the ligaments where intentional attached in a manner to reduce shoulder mobility in order to speed recovery and reduce the chances of injuring the shoulder again. I know next to nothing about the topic of shoulder surgery.
Increasing the range of motion in a joint does not necessarily make it less prone to injury. Proper flexibility should be chosen base on the fitness goals of the individual. For my own part my shoulders need to be flexible enough to do overhead squats. The main way I maintain this flexibility is by doing overhead squats.
I would recommend overhead squats for many reasons. In order to overhead squat properly you need decent flexibility in your ankles, hips, and shoulders
