As Alex Rodriguez returns after confessing to using performance enhancers, he raises an important question: when can an athlete truly be considered “clean”? The intuitive answer is that they are clean when the stuff is no longer in their body – or perhaps when their muscles deflate to normal size.

But it’s not that simple.

Performance enhancing drugs aren’t just about big muscles—they’re also about faster, more fluent skill circuits. Here’s why: PEDs cut recovery time and increase energy levels. Skill athletes on steroids can practice more often, more intensely, and more productively than anybody else. Ultimately it’s the skill circuit, not the muscle, that creates performance.  

This is why we see a telltale pattern: before they get busted, many steroid users are famous for their intense workout routines.  It’s also why even badminton players – who hardly depend on big muscles – are occasionally tempted. (Though as this advertisement makes clear, that might make for a more entertaining game.)