I'm age 81, I had my total knee replacement 6 weeks ago (Medacta GMK Sphere). I have rather short legs and limited knee Range Of Motion. So I can't ride an old stationary bike or my road bike on the trainer (both have a forward leaning position). But at physical therapy I can ride with some warm-up their recumbent bikes (more body weight supported by my back). Now I'm doing a lot of walking. Last Saturday I did a 5 kilometer run/walk in 52:50 min. (or 16:30 per mile). I never was a fast walker. Still can't go down steps leading with that leg. Can only do about a 4 inch step.