Springer's muscles have their own muscles to flex, kinda - she can temporarily trade stretch and squish for bounce and strength, allowing her to be pretty strong when she wants to be!
Springer (Sophie) has an elastic body, as you may or may not know. Neat! But one feature of elastic materials is their elasticity itself - their tendency to snap back from being deformed. Most materials have a relatively constant elastic modulus; in other words, they resist deformation and snap back from it, at a particular eagerness pretty much all the time. Springer has the ability to "zip" and "unzip" the protein polymers in her body to either make herself more readily stretch, or in this case, more elastic and springy, which gives her a boost of strength! Her maximum level is about five times proportionate strength for someone of her build, which at her current fitness level allows her to lift nearly 400kg - certainly nothing to sneeze at for a chubby 1m60 music nerd!
LegendarryCartoon originally sketched this for Springer's Twitter account, for use as a cover for a Moment that collected a series of tweets about her meta-muscles and her experience figuring them out. I figured it would be good to properly post this, not only because I like it, not only because it's going to be an important part of creating Springer's upcoming reference sheet, but also because I wanted to take a whirl at coloring it, which I found to be pretty fun!