hi! just so we're clear, there's no "the" surgery, there's a number of surgeries that trans people get: phalloplasty, vaginoplasty, mastectomy, breast implants, FFS, the lot of them. generally, most of these surgical interventions don't do too much to whole body musculature and are more localized, although having/not having a pair of boobies that you weren't/were used to can do a lot to your balance, but that's not the main thing that changes posture, center of gravity, etc.
possibly more relevant to the question, one of the most common medical interventions is hormone therapy, and this will absolutely change your musculature, flexibility, strength, and more. Transfems on E will see dramatic changes in their strength, muscle mass, and flexibility to be much more in line with cisfems, and transmascs will see similar but opposite. it's a super common meme among transfems who are dating cis women that they have to hand over jars to their cis girlfriends to open after starting E. Transmascs often report gaining an inch or two of height on T, transfems often report losing an inch or two of height on E, with no other interventions. Some people see shoe size changes, postural changes, more. there's no universally agreed upon cause for this but the current leading theories are that it's a combination of fat redistribution, muscle mass changes, and changes in tension in various tendons and ligaments. Anterior Pelvic Tilt is probably the largest cause of changes in postural change in trans people (and it's caused exclusively by GAHT), so if you're looking to learn more, that's probably the first thing you may want to read up on!
so to more explicitly answer the question, starting E will add a lot of fat to your lower body and remove a lot of muscle from your upper body, cause your pelvis to tilt, and more, and starting T will add a lot of muscle to your upper body and remove a lot of fat from your lower body, cause your pelvis to tilt, and more.
i'm super comfy with good faith questions btw so if you have more, feel free to ask me!