In the triathlon world there is workout that is called a 'Brick'. It is where you go for a bike ride (like home from work for me) and then immediately go for a run at the end of the ride.
I try to do one a week and I knew right away why they are called bricks. It has nothing to do with building your exercise one on top of the other. No, it's called a brick BECAUSE THAT"S WHAT YOUR LEGS FEEL LIKE!
The craziest part about it is that once you fight through the first km or mile of the run your legs actually start to feel better. I did a brick yesterday. It was same usual fight through the first mile of the run, but then I felt better. My run is slower coming off the bike, but that's to be expected.
Six weeks of training left, plus race week. Maybe I should start swimming a bit?