Today I began stage 2 of the rehab process. Alternating walking and running for 40 minutes - went very well indeed, no problems whatsoever. I will now gradually increase the time from 40 to 70 minutes over the course of the next 18 days or so and if all goes well (which I expect it will) I can move onto stage 3 on 28 January.
Before this morning's 'run' I weighed myself (as I do before all my runs) and found that I now weigh 133.4 lb (60.5kg). That's at least 7 pounds (3.2kg) too much!!!
I was very surprised as I'm still doing lots of cycling, strength work and stretching to maintain fitness as much as possible. Now I know I've got something else to work on besides running fitness.
I'd like to thank Gary B for the link on his comment to my last post. I read the article on Peak Performance Online and found it very helpful indeed. One thing mentioned is the need to maintain a good nutritional regime, especially post training in terms of protein (to help muscle recovery) and vitamin C & zinc to help fight off infections of the upper respiratory tract. When this is combined with sensible training which includes hard days and easy days I personally don't think Gary need worry about "muscle tissue breakdown leading to loss of muscle mass and strength losses."
One last thing - I came across this brilliantly researched article recently which attempts to answer the question "why do men run ultras?"