I walk Bentley 15-20 mins twice a day. I think that's about 1 mile. He plays 3-4 hours straight after our walk, so he's definitely NOT tired. I don't know if it's bad or not for the knees? I even thought about increasing the time for our afternoon walks since it is cooler and windy... Bentley just wants to keep going and going. Of course he stops many times to sniff around and drink water