Learn Farsi: جلسه به جلسه، تاندون قوی می‌شود و دامنه‌ی حرکت آن گسترش می‌یابد. - Session by session, the tendon gets strong and its range of motion expands.

This is an example of gradual reduplication. By repeating the noun jaleseh (session) with the preposition be (to) in between, it creates the meaning 'session by session' or 'from one session to the next'. You can use this pattern with many nouns to show gradual progression, such as ruz be ruz (day by day) or ghadam be ghadam (step by step).

Could I use gostaresh mishavad instead of gostaresh miyâbad for 'expands'?

No, gostaresh (expansion or development) forms a compound verb with yâftan (to find), not shodan (to become). Literally meaning 'finds expansion', gostaresh yâftan is the standard way to say 'expand' or 'develop' in formal Farsi. In the present tense, the stem of yâftan is yâb, making it gostaresh miyâbad.

What is the literal meaning of dâmaneh in the phrase dâmaneh-ye harkat?

Literally, dâmaneh refers to the 'skirt' of a garment or the 'foothills' of a mountain. In abstract contexts like this, it takes on the meaning of 'scope', 'extent', or 'range'. Therefore, dâmaneh-ye harkat is the standard translation for the physical therapy term 'range of motion'.

Could I replace ân with a possessive suffix to say 'its range of motion'?

Yes! Instead of using the independent pronoun in (the range of motion of it), you could use the possessive suffix and say . Using simply makes the sentence slightly more formal, which fits the clinical or scientific tone of discussing tendons.