Our Maggie will be 5 in April. She has always run that way, like a rabbit exactly. She is perfectly fine as far as we know. She runs like the wind and tumbles and spins to quickly change direction when she is playing. She outruns her boyfriend.
I have tried to watch big dogs run, and when they get going I think they run that way too.
My vet has never said anything and she goes yearly. She goes this week or next, so I will ask. Sometimes I am afraid to ask...when you think everything is fine it stinks to have it crash down around you.
Here is a video of her chasing a bird. I think you can see her back legs running like a bunny.
https://www.youtube.com/watch?v=vq_nUJIdiCs