The soleus muscle, which is used for standing and walking, is better at grabbing creatine from the blood when there’s not much of it around than the fast-twitch muscles in your leg, like the extensor digitorum longus.

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.

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.