Researchers from Tokyo Metropolitan University have developed a way of mapping the distribution of carnitine in skeletal muscle cells. Carnitine is a compound that helps transport fatty acids and reduce metabolic byproducts. They discovered that slow-type muscle fibers contained the most, and that activity promptly led to rises in acetylcarnitine, a product of the immediate response of carnitine contained in the cell. Their technique promises new insights into how muscle cells work.