Leucine is emerging as the "key" amino acid insofar as regulating protein synthesis, stimulating mTOR etc. However, taken a face value and you'd think it's all you need. Here's a good example..
https://ergo-log.com/leucine-after-stren ... uscle.html
Peri-workout dosing of leucine is indeed important. However, the absence of even a single ESSENTIAL amino acid will stop protein synthesis in its tracks. That's why you see all 9 (in very specific ratios) in Synthagen. That left unsaid, many athletes just load in the Leucine. BIG mistake. An imbalance of one amino vs another can do you more harm than good.
Understand leucine is a key player, but one of many...