Avoiding common shoulder injuries.
There's nothing worse for your fitness goals than needing to stop exercising due to pain. Unfortunately when it comes to the most common shoulder injuries, they tend to sneak up on you without an accident or incident that comes to mind once the pain starts. This is because the pain is usually swelling related (even if it doesn't look swollen) and is most often the cumulative result of incorrect or outdated exercise form and the resulting imbalances.
Remember these moves?
The behind the head lat pulldown and shoulder press were once staples in bodybuilding and strength training. Yes, that's the terminator performing a shoulder press back in his competitive bodybuilding days. While once they were among the most popular moves in the gym, today they are rarely seen, and even less often recommended. The simple reason is that as the head is dropped forward and the arms are leveraged backwards, most peoples shoulder mobility is exceeded leading to grinding and rubbing in the shoulder socket. Although it doesn't necessarily cause any immediate pain, a few weeks of training adds up to hundreds of reps with bones and soft tissue rubbing on each other. Swelling slowly builds up in the connective tissues (muscles, tendons and ligaments) inside the shoulder socket leading to cumulative growing pain. At this point the only way to recover is to rest and stop creating additional inflammation, and physio is often needed before you can begin training again.
As I said these example exercises are rarely seen these days, however dumbbell shoulder exercises are still among the most popular and generally effective moves to develop strong stable shoulders, and one of the most common mistakes that can be observed in almost any gym on any given day is allowing the hands and/or elbows to pass behind the shoulder during exercise. Imagine a line through the middle of your head and body that separates your front half from your back half. Simply put, if you are doing a shoulder press or shoulder fly's your hands (and the weights) should always remain in front of that line. Aim for 45 degrees as a general rule. If you can see the weights in your peripheral vision as you raise and lower them, then you are in a significantly safer position.
I didn't need to go very deep into google images to find an example of this all to common mistake. If you compare the images above and below, you can easily see that the above lift has the arms too far backwards, and is likely to eventually lead to pain and injury. In the lower image the elbows are in front of the body, allowing the shoulders plenty of space in the shoulder joint for everything to move well and friction free.
I know someone out there is saying to themselves that they've always done presses/pulldowns behind the head and have never had an issue, and while this is possible for people with great existing shoulder mobility and stability, which can be developed, to perform these moves behind that midline we just drew through the body; most people lack the needed functional range of motion to safely and effectively get away with it. so keep the bar/weights in front, and you'll be significantly safer.
If you're unsure about your form, most gyms have someone who can take a quick look to tell you if you're at risk; and if you're experiencing exercise related shoulder pain it's worth getting checked out and cleared for exercise by a physiotherapist before continuing and risking further pain and injury.
I hope you found this useful, and wish you a lifetime of injury free fitness and health.