That's right. Doesn't matter how strong they are; if they're human, their joints have a limit to how much they'll bend.

[ His breath caught for a moment as she moved... but now wasn't the time. Her hold wasn't quite complete, and with some quick application of his limbs, he slipped loose. ]

It ain't just about who's bigger. If ya feel them trying to slip ya out of position, you move to regain it, and work toward what you want to happen. You're gonna get better at it; you've already got a better sense of your own body than most people.

[ A... great sense of her own body, in fact. ]