In reply to alasdair19:
Listen to your body. It will tell you if something's going to break. We are all different and adapt at different paces. Do as much as you think you can do and gradually increase it as you see fit. All the 'no more than 10% increase in distance' is hyperbole and usually people can do much more than they think.
In vest in a descent pair of trail shoes (not road shoes), get outside and make like Forrest Gump - Run Forrest, Run!
Oh, and make sure to stretch/massage with foam roller after running. Makes a world of difference to achey muscles.