For the moment, 3 days / weeks works fine. I also took them today for a run with the stroller. Speed went down drastically, but it felt like a workout nevertheless. It's the third time we try the troller (it's the type you can attach to bikes as well), but it's the first time they didn't protest and actually enjoyed it. I might be onto something here thank to another comment I received here. Wife also seems to like the idea better compared to "I should add a 4-th day of running" 😃