I wouldn't class MP a junk, it comes at the slower end of the tempo range. I also wouldn't include MP miles in my 20% quality, but would be wary of doing too many. I think Daniels suggests that MP should be 20% of weekly mileage max?
I steer clear of anything between MP and easy, so for me at the moment anything in the 7:40-8:40 range. It seems to be working!
3 easy miles this morning. Shortest run only workout for a while.
Seren, I think 20 miles would take more out of a 10 minute miler because both runners will have roughly the same cadence, so the slower runner will take a lot more steps to complete the run, a lot more impact on the legs and other associated issues.
So you were running once a week, increasing the mileage every week, and got injured? Not a suprise.
Run off road, 3 times a week, slowly. Get proper shoes by going to a proper running shop and getting assessed. Build up mileage, again slowly, but keeping to 3 runs a week. Get to a 6,6,10 and that should see yuo round.
To answer your original question - you may get round off good fitness all round, but it will destroy your shins. Much better to address the problem.
Take it easy, do the right things and follow the physio's advice. If you're fit enough to run the half, then run it, if not then don't. There are loads of half marathons about, pick one you can train for properly once you're fit and do that one instead.