When scientists lowered the sodium levels around rat muscle cells, the cells absorbed much less creatine—showing that sodium is needed for creatine to get inside these muscle cells.

Your muscles use a special door called SLC6A8 to let creatine in, and this door only works when there’s more sodium outside the cell than inside — like a pump that needs salt to open.

A chemical that looks like creatine can block muscle cells from taking in creatine — in rat muscle tests, it stopped 82% of the creatine from getting in when used at a certain strength, which means it might be pretending to be creatine to get in first.

Scientists found that rat leg muscle cells absorb creatine at a specific speed and capacity—like a sponge that can only soak up so much water before it’s full.

In a lab dish, adding insulin doesn’t make rat leg muscle cells take up more or less creatine, even when the insulin level is normal for a living body.

When your cells take in creatine, they also pull in sodium, which makes the inside of the cell saltier. To balance that, water rushes in, making the cell swell up a bit.