Implementing Race-Sim Runs

From the beginning of my half marathon training plan I told myself that I may (and probably would) have to adjust my plan according to how my body feels.  Well this doesn't have to do with how my body feels, but I really like the idea of incorporating race-sim runs into my training plan.  A race-sim run, from what I gather is similar to a tempo run, but instead of waiting until the day of the race to feel what running on lead legs feels like, you feel that during a training run :)  So I think when I get closer to my longer runs, that I am going to switch a tempo run here and there for a race-sim run.  I got this idea from Meganerd Runs and I am super interested to see what it is like!

On another note I need to get some new running shoes pretty soon for the half, any suggestions? I currently have a pair of Nikes and a pair of Adidas, I like both, but I think I prefer my Nikes.