Protein concentrates are categorized as nutritional supplements whose positive effects have been demonstrated by serious studies. Their use in sport can not be questioned today. The reason for their use is the fact that taking a quantity, even low protein after strength training can stimulate muscle protein synthesis and is believed to reduce muscle protein catabolism - in this way we obtain an increase in muscle mass and strength. In a recent study (2006) in International Journal of Sport Nutrition, researchers from several Canadian universities have set out to prove this hypothesis. Moreover, they wanted to see if another hypothesis is true: use of whey protein leads to better absorption and utilization resulting from the digestion of amino acids than soy protein administration. Both the whey proteins and soy proteins are considered high quality, with a relatively high percentage of essential amino acids required for muscle protein synthesis.