Illness during marathon training

Any advice would be welcome on this one!

I've been ill with a couple of virus type things for nearly two weeks and am getting massively concerned about getting my fitness back and training back on schedule for London marathon 6 weeks today! Thought I was better last week and set out for a 15 mile run but only managed 6. Feel very lethargic and like I'm losing my running mojo! How do I get back on track? Should have run 15 today, 16 next week, 18 the week after etc...Because of various injuries, I do half my training on cross trainer and just one other 6 m run per week.

Would be really grateful for any advice on this! Do I wait til I'm 80%/ 90% or 100% and what distance should I go for???? Thank you!

There is a balance with exercise and the immune system. At the right level exercise improves the immune system and will help fight viruses but too much exercise and the immune system suffers. As a result it's quite common for people to pick up colds after a big race, especially a marathon.

So in theory light exercise should help you fight your virus. I've heard you shouldn't run with a temperature though, as this places quite a strain on the body, especially the heart.

If you virus isn't settling though it's worth having a check up with your GP (if you haven't already).

It might be worth focussing your energy just on the running rather than doing cross training too. Stick to a slow pace and just do the endurance work (no speed or hill work) until you feel better. Maybe run 30secs to 1minute per mile slower than you'd expect for your distance work and see if that's easier on your body.

This might help too

http://www.runnersworld.com/article/1,7120,s6-242-300--13452-0,00.html?cm_mmc=Twitter-_-RunnersWorld-_-Content-Nutrition-_-HealingFoodsDrinks

There is advice on colds on the second page I think

Plus this one too

http://www.runnersworld.com/article/0,7120,s6-241-285--14078-0,00.html?cm_mmc=Twitter-_-RunnersWorld-_-Content-MindBody-_-ImmuneToItAll

Huge thanks Tim, will check out the articles.