I’ve been dealing with a similar, over extension issue myself.
Like you, after awhile my scapula and then my hips felt “frozen,” just kinda locked into a bad position.
Push up plus and scap pushups have been good to restore motion. I also like “band shoulder tractions” where you use flex bands to assist the stretch.
For hips and glutes I’ve been doing tons of clam shells, hip hikes, seated abductions with bands around the knees, and seated Psoas lifts/holds with a mini band around the knees. Anything to get my hips mobile, and my glutes working to get my pelvis underneath me. And to keep my spine neutral.
Like Trevor mentioned, weak hamstrings are part of the issue. I don’t know if weak hams made me overextend, or if being in over extension made them weak, but my hamstrings were garbage. I’ve been doing hamstring curls of all kinds ( 1 leg, 2 leg, standing, laying, bands, ankle weights) to get “connected” to them better. Then inverse curls (a bodyweight calesthenic, like an easy Glute/Ham raise) to try and move better.
For other stuff, 1 arm farmer’s walk and sidebends have helped me get the obliques going, to help with posture, and a neutral spine.
Lunges with a dumbbell held on one side are good too. The off set weight challenges hip stability while moving around.
Thank you for the response! Is your posture similar to mine shown here? I’m guessing that I have the same situation your describing and I’ll try all that you posted… My overall guess is that I have crazy overpowering quads from being explosive in volleyball and my erectors are very hypertrophied from the loading phase of spiking a volleyball. Going to really try hitting my inhibited glutes and hamstrings to bring the hips to neutral and a little core work as well!
Found a few good videos on YouTube on reversing this and said it takes a few weeks so I’m hoping this corrects my thoracic spine positioning since I know it can’t be a weak upper back necessarily because I’ve been doing upper back work for way too long with somewhat good results but I’m reach to fix this pelvis now. Oh the negative results of playing a power sport and being too active… Haha