My number one impediment is probably just being out of shape in general. I run out of breath after a lap of freestyle. However, the masters swimming coach (Emily) has been giving me a bunch of tweaks: how my arms enter the water, working on my kick, my breathing (exhaling specifically), and all sorts of little things. It seems that 50% end up working well for me. It’s hard to hold it all in my head, but the uphill swim seems to slowly be paying off.