Your muscles need sodium to pull in creatine, kind of like a battery-powered door — if the battery's dead or there's no sodium around, creatine can't get inside, even if you're drinking plenty of water.

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.

When creatine gets into muscle cells, it brings sodium with it, which pulls water into the cells and makes them swell up a bit — like a sponge soaking up water.

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.

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.

In regular human red blood cells, about 40% of the creatine that gets inside does so using a special sodium-powered process, which means this system plays a big role in controlling how much creatine is inside the cells.