Our Whippets are relatively young, but our oldest Greyhound, Misty, 13, has very shakey back legs. She can't go up stairs any longer, and even has a hard time stepping up into the house from the front porch or our garage. She's still happy, though. I'm a believer in exercise, but I don't think it will help Misty. She tries to run when the other kids start flying, but she can't go far before she has to lay down. She also has congestive heart failure.