Carnitine is found largely in muscle. The amino acids methionine and lysine form carnitine in the kidneys and liver.(19) The bodies main source of energy ATP(adenosine triphosphate) is mainly created in the mitochondria of the cell. Carnitine helps pass fat across the mitochondria where it than can be burned and essentially turned into energy in the form of ATP.(20) Carnitine almost acts as an intermediate in the fat loss stages between fat being stimulated from the cell to being burned off for good later. Studies show that some of Carnitine ability to decrease muscle soreness could relate to its ability to enhance nitric oxide (NO) levels(21), which helps with blood flow, delivery of oxygen and muscle growth.(25) Carnitine also has abilities to increase the amount of androgen receptors, inside muscle cells. These are crucial as testosterone binds to these androgen receptors.(22)(23)
Testosterone helps to stimulate muscle growth.
Another way carnitine increases muscle growth is by stimulating binding proteins that increase insulin-like growth factor-I (IGF-I).(24)