Your puppy is thinner than mine.
I don't know why she doesn't walk much at night, anymore. I'd say it's because she's overweight, but that never stopped her before. We'd walk six miles a day. Now, she walks just fine in the morning, but normally doesn't want to walk much at night (it's still sunny out, so it's not because it's dark). She walked pretty good the past two nights, but not so far tonight.