Leucine is taken afterwards so we secrete insulin which is anti-catabolic.
Leucine is more-so taken to ensure/increase mTOR signaling, not to spike insulin.
Aha, so why not take it before?
If you're not providing substrate, also, to support the anabolism, would seem kind of pointless, to me.Plus, since lifting itself creates a catabolic environment, I'm not sure it wouldn't just cancel out the effect. I don't know, though.