I have just finished week 3 which I found quite hard. I found it hard running 3 mins non-stop as I used to smoke so my lungs are buggered. The third time of doing it was easier than the first time though! I don't know whether to do week 3 again til it gets easier or move on to week 4? Week 4 looks quite hard with 5 mins of running non-stop. There is also 16 mins of running in total versus 9 mins in week 3, so it is quite a step up.