Walking is not a fallback.
It is:
Active Recovery
Aerobic base building
Stress Reduction
If running feels like too much today WALK.
Movement is movement.
Walking the dogs is a perfect opportunity to prime yourself, and the pups, for fitness progression. 15 minutes can burn approximately 100 calories in less than 1.5 miles and also feed muscles oxygen and blood in between more intense workouts. It's one of the keys to actually recovering.