In a novel I was reading I found this passage
右腕を抱き、ため息に体をしぼませた。
The context is not that complicate, as the character arrives in a new home and it's tired so he does this.
What I'm confused, is what to make of the に here? I understand 体をしぼませた。 is "My body deflates/sags" but how is the sentence interacting with ため息?