Refers to innate potential or natural ability that can be developed. Often used with ある/ない or in phrases like 素質がある (have the makings of).
She has the makings of a pianist.
素質はあるけど、まだ練習が必要だ。
He has talent, but he still needs practice.
nature; character; temperament
Refers to one's inherent disposition or constitution, often in a medical or psychological context. Less common than sense 1 in everyday speech.
彼はもともと神経質な素質だ。
He is naturally of a nervous temperament.
この病気は遺伝的な素質が関係している。
This illness is related to a hereditary predisposition.
He has the makings of a singer.
Education that develops a child's natural talent is important.
The coach recognized the young player's hidden talent.
She is blessed with a natural talent for music.
素質 is the general word for innate talent or potential, while 筋 in this sense is more colloquial and often used about skill in sports or arts.