Hi!
You highlight an important point that is sometimes overlooked.
What we could call the "physical condition" of the pianist.
Piano practice involves different postures, muscles, tendons, etc.
If the practice is intensive for a long time, we begin to suffer tension and even pain in different parts of the body.
Sometimes the weak point is the back, or could be the arms, wrists, neck, etc.
They limit the practice time by causing discomfort or pain.
The solution may be to attend a gym and do exercises that strengthen the muscles and give them flexibility.
The improvement may be noticeable.
Perhaps pianists should do athletic exercises to improve muscle strength.
And it is also very important to maintain proper breathing and oxygenation during piano practice.
I hope you get better soon.