Running on Trashed Quads

I intentionally ran fast downhills for a few Ks yesterday. I wanted to see what effect it had on my knees and leg muscles. The Knees are 100% but I do have a bit of pain in my Quads. I have had allot worse pain in the quads. I was thinking about a reset day today but instead I jumped on the treadmill on my lunch (working today) and did a 10K run. It took a few Ks to get up to a 5:00 pace and the legs hurt a bit. The experience was very similar to how the legs feel in the late stages of a Marathon...good training I would Say!