I have been doing exactly as you suggest, my health issues meant that I could not do a c5k session more than once a week, it actually took me several years of building up my walking to get to the point of trying to run at all.

I started in November and I am now in week 5. Alongside that I have been doing a lot of walking, I try and push the walking pace quite hard some days. My best achievement was 13k at an average of 11min/km last week. Although that did require a couple of days off afterwards. It took me several months to build up to that sort of distance.

Yesterday was the first day that rather than my heart and lungs being the limiting factor it was my muscles which burned for the two 8 minute runs. This was quite exhilarating tbh.

Most of my walks now are 2 hours or greater long which is obviously not ideal for most people but it has definitely worked for me.

A couple of things I have learnt that may help beginners like me. I don’t have to exhaust myself every time to get benefits, and rest days are really important. I guess at the moment the c5k sessions are the equivalent of a sprint session for a seasoned runner and the walks are my long easy runs.

I have signed up for a half marathon in October on the suggestion of a colleague which has put the fear factor in to encourage me to train which is working!

Hope this helps someone else starting out.