Arginine was isolated from a lupine seedling in 1886, but it wasn't until 1932 that scientists linked it to the creation of urea, the waste product necessary to remove toxic ammonia from the body. Several years later, researchers also discovered L-arginine was needed to make creatine the chemical important to muscle contractions and performance during exercise. Arginine is considered a semi-essential amino acid because the body can produce it but supplementation is sometimes still needed. People with protein malnutrition or other nutrition concerns may not have enough. A sufficient quantity of arginine is especially important in the diets of children, especially those experiencing growth. It is also involved in ammonia detoxification and immune function.