I have just completed week 5 run 3 and managed to cover 3,070 metres in 20 minutes.
What a challenge! As Michael Johnson says in the app, it's as much of a mental challenge as a physical one.
I'm middle aged and I've not run since I was a child. The biggest surprise is how, after some very difficult early weeks, my heart, lungs and legs have quickly got up to being quite fit.
What's been much harder and of far greater concern is taking care to run heel first without letting my toes twist out. Also, to make sure not do anything silly like tripping or falling into little potholes or off kerbstones.
Insoles and concentration are my running watchwords. I'm very overweight (1.85m, 116kg) and I'm at a high risk of injury so having to be ridiculously careful with my legs. They're still working though, on to week 6!