Andrew Huberman· PhD
If you look at your soleus, which is the smaller one that goes in the back, that's generally mostly slow-twitch, typically 80% or so slow-twitch. The gastroc, which is the other one right next to it. So if you were to point your toe next to your face and that part that kind of flexes out in the middle pops out, that's your gastroc. That is almost the inverse. So it's generally 80% fast-twitch, maybe 20% slow-twitch.