Being mobile is a crucial aspect of being healthy. If a person is not able to move a joint freely through its full range of motion, then they are already putting themselves at an increased risk of injury before even attempting to pick up a weight and load that range of motion. There should be a period of time either before/after training or even on a separate day that is dedicated to improving mobility. Something as little as 5-10 minutes daily can be enough to see progress. One of the most common reasons you feel un-athletic is because you aren't able to get into the positions and postures that you want. It's much easier to do a little mobility work every day to preserve it than it is to lose it and have to work to get it back. 5 minutes a day goes a long way.