It has been a grand total of 5 months of a standing desk. My ankles and knees used to hurt at first and were regularly sore. After a couple months I built up enough muscle to completely counteract the new muscle strain in my knees. Only just a couple weeks ago my ankles became strong enough to no longer feel sore after a long day. From the beginning, however, my back has never felt better, especially when combined with a long night of rest. I don’t see myself going back to a sitting desk ever, if I can avoid it.