In resting muscles, the way energy molecules move isn't slowed down by how far they have to travel — they can get where they need to go just fine.

In resting human muscles, a molecule called phosphocreatine can travel far enough to deliver energy where it's needed, even between distant parts of the muscle cell — kind of like a tiny energy shuttle making the rounds.

In healthy human muscles, a molecule called phosphocreatine moves around at a specific speed when there's nothing blocking it — and scientists use that speed to understand how energy gets shuttled inside cells.

In healthy adult muscles, a molecule called phosphocreatine doesn't move freely — it's kind of boxed in by cell walls, and the size of those boxes matches the size of the muscle fibers themselves.

In healthy adult muscles at rest, a molecule called phosphocreatine moves more easily along the length of muscle fibers than across them—like sliding along a hallway instead of pushing through walls—because the muscle's internal structure guides its movement.