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Whey protein contains all the essential amino acids (EAA), including the branch chain amino acid Leucine, and has the highest protein quality rating among other proteins. Whey protein supplementation prevents the decline in serum amino acids that occurs after resistance training, and increases amino acid availability. As more amino acids, especially EAAs, are available to the muscle, increased strength and muscle growth are seen. Current research with whey protein has shown that additional leucine given with whey can increase strength and lean muscle mass more than whey protein alone. Greater benefits of whey protein on muscle strength and muscle size are seen when it is taken before and immediately following a resistance exercise session. In a recent study published in the Journal of Strength and Conditioning Research, young men were given either a supplement of 20g whey protein plus 6.2g of leucine, or an equal caloric supplement of carbohydrate (26.2g of maltodextrin), 30 min before and immediately after leg training. The men in both supplement groups trained their non-dominant leg 3 days a week for 8 weeks. On non-training days, the protein or carbohydrate supplement was only taken once per day. After 8 weeks, both groups increased the size of the quadriceps muscles of the trained leg. However, only the men who consumed whey + leucine supplement also had an increase in the size of the vastus lateralis muscle of the non-trained leg. This suggests that whey + leucine has the ability to increase quadriceps muscle size without exercise. Furthermore, the men who consumed the whey + leucine supplement significantly increased leg extension strength in the trained leg by 30%, while the men who consumed the carbohydrate supplement only increased leg strength in the trained leg by 22%. Interestingly, the increased strength found with the whey + leucine supplement was not accompanied by greater muscle hypertrophy. This indicates that whey protein supplementation had an ergogenic effect on exercise performance that was independent of changes in muscle size. Even more interesting is that the men who consumed the whey + leucine supplement also increased the strength of their non-trained leg by 14.5%, while the carbohydrate supplement had no improvement at all. Overall, this study offers important implications for many athletes. First, to achieve the most strength gains from resistance training, include a whey protein supplement with additional leucine before and immediately after exercise. Second, if an injury prevents training of a certain body part, whey protein can help maintain strength and increase muscle size.

Coburn JW, Housh DJ, Housh TJ, Malek MH, Beck TW, Cramer JT, Johnson GO, Donlin PE. Effects of leucine and whey protein supplementation during eight weeks of unilateral resistance training. Coburn JW et al. 2006. J Strength Cond Res. May;20(2):284-91.