I don't know if you've tried this yet? Regular weight (machines) room for toning the arms, shoulders, and upper body muscles.
Also collagen supplements such as this one:
("move free"). I'd found it helped me recover quicker from tennis elbow
or whatever ligament or joint pains by just a pill or two in a a few days (of course, it can vary by individual).
Pretty amazing. I didn't make it past high school orchestra (violin about 5 years since middle school), and probably too finger dyslexic, with bad tonal hearing and judgement, to ever make it into good 5th position and beyond form, always missing the tones.
I also did more piano for years ('gave up' on tennis at 10yr old then did the hours on piano during my school years, then back to tennis years later), took some college sessions.
But I'm nowhere talented I realized at the end many years later. With tennis, It helps me with the exercise as I dislike or am too bored of typical cardio,
but I'm not naturally talented as well. I do like practicing tennis in "drill" like fashion similar to the past violin and piano, where getting to some performance I would agree can be somewhat 'mentally similar' to playing
a classical musical instrument, but I guess my fingers' calluses and cartilage has built up too much in my right hand now to be too stiff for piano anymore i.e. two of my fingers is always slight "stuck" joint, stiffer,
and grip worn from tennis (using a 13+ oz wilson kps88) and my hands were always small for the weight room (I probably have to start using protective gloves).