Leucine is an essential amino acid which plays an important role in protein synthesis and many other functions including the regulation of blood-sugar levels, growth and repair of muscle and bone tissue, growth hormone production, and wound healing. It also prevents the breakdown of muscle proteins after trauma or severe stress. It is leucine which provides the signal to switch from a catabolic state, in which muscle tissue is being broken down, to an anabolic state in which it begins to rebuild. The quicker your body receives this signal after training, the sooner it switches from breaking muscle down to building and repairing it to ensure a full and speedy recovery.