>>76408810 (OP)It depends there might be multiple different sources.
1. Crush on fit girl when teenager
2. Getting fit, slow admiration to muscle
3. Some positive experience with strong girl at young age
Personally mine is a bit weird?
My parents were strict on porn and as young teenager you really get horny easily.
My mind kinda processed it that. Nude girls, boobs, tits are banned and evill. So naturally it found different thing to admire. (to this day I remember when I saw girl armwrestling which I found hot).
Overtime I developed a fetish.
But idk, I don't even mind it much.