It is not uncommon to hear people mention shoulder movement at the bottom range of motion of dips, either as a sign of going 'too deep' or risking injury. Is this true? Are dips dangerous for the shoulders? Is shoulder movement a sign you are going 'too deep'? The short answer is no. The slightly more nuanced response is that it depends on the individual performing the exercise (yes, I know, it may sound a bit boring), but let's discuss.
Let me be direct. The idea that shoulder movement/sliding is a sign of too much depth is completely and it's utterly unfounded and arbitrary. I’m not sure exactly how this idea gained prominence, although I have my suspicions (aside from people using any excuse to cut their ROM or excuse away their shorter ROM).
"But It looks painful! Why allow shoulder movement?”
As you go deeper, shoulder movement is inevitable. What is also inevitable is a deeper and deeper stretch in the pecs. We know from a ton of research and decades of anecdotal evidence that a ton of growth is correlated with the eccentric and stretch positions in resistance training. So back to the question, why allow the shoulder to move? Hypertrophy, damnit!
“Okay fine, but it still looks too risky, despite the growth potential.”
Fortunately, how things look and how things feel are two totally separate things.
There are no hard and fast rules to determine how deep you should go outside of these 3 important factors.
Experiencing Shoulder/Joint Pain - First, and most importantly, if you experience sharp pain in your shoulders (or your elbows) then either this entire exercise isn’t right for you or you won’t be going super deep. This is just part of lifting, sorry for the bad news.
Controlling The Movement - Are you in control of the movement? This means no dive-bombing the eccentric and lifting like a goon, overall. If you are controlling the movement then good, if not, fix that immediately.
Ability To Produce Force From The Bottom - Are you able to produce a lot of force from the bottom position? If the answer is no, then you're going too deep. Ideally, you want to go deep enough to where you can both take advantage of the hypertrophic stimulus of the loaded stretch position while also being able to produce strong contractions during the concentric phase.
I believe the misconception originated from a large population of individuals with pre-existing shoulder issues who were unable to perform dips in this manner. The idea being that if moving the shoulders forward during dips causes pain, it might lead to the mistaken assumption that there was excessive range of motion.
However, this interpretation would be incorrect. Formulating a general rule for everyone based on the experiences of individuals with pre-existing shoulder injuries represents flawed logic when working backwards.
You can and should go as deep as you can as long as you are not experiencing pain, controlling the movement, and able to produce force from the bottom range of motion.
Final bit of advice: The dip is an advanced movement in that a lot of experience is required correctly determine the 3 factors listed above. Someone new may not have the control necessary to feel out the dip and experiment with depth like someone with 10 years of experience. So, fair warning.
John Meadows and other Greats Performing Dips with shoulder movement -- Notice the stretch in the pecs in the second picture*