How’s my sister stronger than me?

My sister was visibly stronger than me growing up, I was just always more aggressive.

I’ve been exercising for about 4 months now & put on a tiny bit of muscle
Yesterday I arm wrestled with my sister and we were about even..

She might’ve had a slight edge on me but we would’ve been arm wrestling for hours

How is she still stronger than me?
She doesn’t exercise at all..
What am I doing wrong?

by the way we’re the same size
weight & height
don’t imagine her being way smaller than me
How’s my sister stronger than me?
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