Welcome Renee!

I use a treadmill as my crosstraining - I'm also a hiker, so it makes sense. I don't run on it - I also have bad knees. I put it on the highest incline - 25% grade (it's a treadmill designed for hikers) and go slowly - 2 or 2.5 mph. I've built up to that slowly - important to build up slowly. If I've been off for a while, then it's 2 mph at 10%. Moderation is key.