That was the result of a 2009 study published in the Journal of the International Society of Sports Nutrition.
The study lasted 8 weeks and involved 36 resistance trained men. Participants received either 14 grams of Branch Chain Amino Acids (BCAA), 28 grams of whey protein or 28 grams of a carbohydrate drink.
At the end of the study the BCAA group gained 8 pounds of lean muscle mass versus 2 pounds for the whey group and 2 pounds for the carbohydrate group. The BCAA group also experienced greater reductions of body fat and greater strength gains.
My favorites are:
Scivation XtendInner Armour BCAA PEAK
Cytosport Monster Aminos
USPLabs Modern BCAA
Vitaminshoppe BodyTech BCAA Powder
Allmax Nutrition Aminocore
Optimum Nutrition Amino Energy
Dymatize Nutrition Elite Recoup
If you aren’t seeing the gains you think you should, maybe try a BCAA cycle.