Running distance over time. I still can't run 5k without walking about 20% of the way.
And it's not going fast either, but I'm still proud of the progress. The data is keeping me going.
EDIT: Thanks for the support! The legs still don't want to do, what I want them to. But they will learn, who's the boss eventually.
If your knees are hurting, your running technique is likely wrong. I know a lot of people start off running heel to toe, which is backwards and puts a ton of stress on your knees.
For those who don't know, you're supposed to land on the ball of your foot, which basically turns your lower legs into a shock absorber for your knees.