Before I started biking, I used to walk briskly 3 miles about 5 times a week.
Once I started biking, I stopped my long walks.
Recently, I did my walk with my daughters when they were visiting- I was REALLY SORE the next day. Then I walkd again a few days later, and was not so sore the next day.

Fitness walking uses some muscles we don't use much when biking.

I'm going to try to do my 3 mile walk at least every other week now, so I don't lose it all again.