I run pretty good mileage. 100+ a week. Now I have the odd urge to add 2 mile runs on the treadmill. Runs of like 8 minute pace. This is in addition to the already pre-existing mileage.(Not cutting runs short to run on the treadmill) You can say this is a recovery run, perhaps? Does it do anything for me cardiovascularly? I'm looking for the scientific explanation.