I have to do a lot more cross-training lately to keep up my endurance nursing these shins.  When I have a Monday or Friday off during the week, I take a class at the gym called Athletic Conditioning.  It's an hour and fifteen minutes of torture...cardio bursts and then weights (lather, rinse, repeat.)  It's defintely helped my endurance...even though I ran a moderately slow 5k on Friday, if my shins hadn't of started to weigh me down, the rest of my body was ready for three more miles.

I'm actually off to Monday's class in about 20 minutes.