She has always been walked 2 x per day. 5kms in the morning. 3kms in the evening.
In spring, summer and autumn, I do couch to 5k. She comes along with my other dogs. It's a gradual build up to 5km.
She's 4 yeRs old and she really struggles. I make sure we go out at cool times of the day.
Why doesn't her fitness improve?