I'm sure reams have been written on calf muscles or calves, just adding my two cents here.
I think it's really important for beginners, even if you consider yourself reasonably fit (which was my case) to build up their leg muscles bit by bit, using the days in between runs to do a few simple exercises to that end.
It seems that a lot of people experience pain, discomfort and even injuries because their muscles are just not ready for the the demands being made. Stress on legs/ muscles is talked about here healthunlocked.com/couchto5... , but I cant see any reference to specific exercises...
I had to change my routine at week 4 as my calf muscles couldn't cope with the extra demands. I didn't run from Mon - Fri, but I did walk. I found some online exercises for building up muscles which I found useful.
runnersblueprint.com/best-e...
running-physio.com/calf-str...
Then I went on my own regime and instead of doing WK4 I made up a routine doing 1.5 - 4.5 mins of running interspersed with 2 - 3 mins of walking. Today I did 5W, 3.5R, 1.5W, 4.5R,2W, 5.5R, 2W, 5.5R, 5W (R=run, W=walk), so 19 mins running and no problem with muscles.
I'm really happy with the results and will continue to do the leg strengthening exercises. The next time I go for a run I'll try W5R1 which is 3x5mins running, but I might not go from that to 8mins in W5R2. It might be too much of a jump.
By writing this I hope people who are finding the jump in mins too much will see that there's not only one way of doing this and also that muscle prep, even for just a few mins run is a good idea.
Happy running everyone, hope we all make it to the end