Did you know that although Leucine is one of the Branched Chain Amino Acids (BCAAs) and undoubtedly has a key role in promoting muscle growth and recovery, its main mechanism for this is to signal muscle synthesis.
Now signalling muscle synthesis (growth) is one thing, but there needs to be adequate building blocks to make it worthwhile! Perhaps the best way to utilise Leucine and indeed your whey protein (or whatever protein source you use) is to consume a BCAA alongside a whey protein e.g. ingest some BCAAs approx 30-40mins prior to exercise, followed by your protein shake as soon after your training session as possible.
Beelen, M., Koopman, R., Gijsen, A, P., Vandereyt, K., Kies, A, K. et al. (2008). Protein coingestion stimulates muscle protein synthesis during resistance- type exercise. Am J Physiol Endocrinol Metab. 295: E70-77.