I’ve had this problem continually for probably a year or so and it comes and goes. But every now and again, like right now for instance, a day, maybe two after benching my armpit will get super tender to the touch. I do plenty of stretching and warming up on bench beforehand too. I’m doing the strong lifts 5x5 and I’ve seen increases in everyone of my lifts except bench press.
3-4 years ago I could rep 225 3x10 quite easily. Maxed at about 315. At 6"0 185, I didn’t think that was too bad. Now, I struggle with benching 185 5x5 and I have this cursed swollen armpit issue. I should note that it doesn’t happen every single time I bench, but way too often if ever.
Which part of the armpit?Nearby the front delt/chest or tricep/lat?
I used to have pain near my front delt when I started to lift and after my shoulder injury.
The first case is because of my bad form and the second is because I lost some shoulder mobility after the injury.
For my case, Stretching and warming up didn’t help.
These are something that helped me after the injury.Hope it helps you too.
This is not exactly for Bench press but it do make my bench press painless.
And This video really help with my bench press and dips.Also his channel has many great mobility video.
Arm Shaking?I guess it’s some control issue.
Any shoulder injury before?
Have you ever record your bench press?If no I suggest you do it.
My left shoulder have serious scapular issue after injury.When I bench the left side is always a lot lower than right side.
Notice this—I don’t even feel it.I only found it when one day I recorded it.I spent a lot of time finding the cause and a month ago I found out that it is my left scapular, then I seem to recall that even before the injury my left shoulder have the click sound every time I roll the arm and pain during press.I did tons of shoulder/scapular mobility work and control exercise.Now the click sound has gone and my bench press are becoming better and pain free(still have some issue but way better than before).
Well it is my personal experience.I hope that can help you more or less.
If it doesn’t, just take this as a suggestion of doing more mobility work.You can always benefit from it.