My 4 month old lab/St.Bernard mix puppy has a lot of energy! I have taken her on walks before but I'm wondering how do I know if it is too much? I want to tire her out but I don't want to do any harm to her either. I have taken her on 20 min walks and she does great, but does not really seem to tire out at all, I did take her on a 40 min walk a week ago and she didnt slow down or try to stop, she did whine a bit at the end but it was hot and I think she was thirsty. Is 45 min too long for a 4 month old? I feel like she never gets tired! I do have other dogs she plays with constantly, but she never tires from that. She also likes to swim but that is something we really only do on the weekends, shes a great swimmer! Any advice would be great, thanks!