Protein supplements high in the amino acid leucine promote muscle protein synthesis.  Dutch researchers combined the results of 22 studies that included 680 people, using a statistical technique called meta-analysis.  Post exercise protein supplements increased fat free mass (mainly muscle) and leg press strength.  The results were similar in younger and older people.  Consuming a supplement after weight training containing approximately 25 grams of protein is an effective way to increase muscle mass and strength in people of any age.  (American Journal Clinical Nutrition, 96:  1454-1464, 2012)