Bill Hartman is a wise man; listen to his thoughts on learning (and other stuff).
I personally use processing (by making my own notes from reading multiple source materials) and retrieval to a certain extent (going back to that topic and reading it and recalling it again) to hopefully turn that grind into long term memory.
But it does take time and focus, and it does burn my brain, more than doing deadlifts.
And in case you just want to watch the video...
http://www.billhartman.net This is a video from Day 1 or my most recent student's internship. We were discussing some of the best ways for him to take in the new information with which he would be presented, how to organize it, and then how to assure that he actually was learning this new information.