I did 9Kms yesterday. I had done several calf raises the previous day so I am having sore calves. Still no injury thus far. I think what has helped me is that I work out at least four times every week besides my Sunday run. I shall keep at this until I can do 16Kms. Then I will consider changing my tact - either by working on distance or speed. I am likely to go the distance way though. I have also shifted work to my left leg somewhat.
This week I will go easy on my calves but do more squats and throw more kicks.
Next Sunday I will be doing 10Kms. I need to buy a scale and start cutting back on carbs and fatty food.