Warms and Cool Downs
You might want to check out spending the first fifteen minutes warming up, at a slower pace, and the final fifteen minutes cooling down, again at a slower pace. This allows your body to adjust to the changes involved in your workout and means you'll suffer from less tightness. I'm no expert, but this is mostly what I do, and I hardly have any discomfort, even when I am doing pretty intense training. I've been doing this for about 15 years. The other thing I suggest is swimming a couple days a week. I do this with a pull-buoy, which allows me to work out while resting my legs. (I also find the pull-buoy has some resemblance to a wet-suit in providing a lot of buoyancy), and in any case, I don't kick during my swim in tris, so it feels fine not to kick in training. It certainly allows my legs some rest.