Speeding up from 50K to marathon

I'm running the London Ultra 50 K on 19th February, and the Greater Manchester Marathon 29th April. Previous longest race half-marathon. I've cut out practically all speedwork while training for the ultra, as a deliberate strategy to avoid overdoing things and injuring myself, which appears to have worked, but my pace has fallen off.

Does anyone have suggestions for getting some speed back into my legs between the two races? I'm expecting to average 10-minute miles at the 50K, but my half time is under 1.44, so with appropriate training I should be able to get under 4 hrs for the marathon (even under 3.50,although I'm not expecting that this time around). I'm running 8 - 8.15 miles on hour-long club runs at the moment (depending on hills) and 9-minute miles on 10-12mile training runs, but averaging 10-minute miles on 20-26 mile runs.

There's not much between 50k and a marathon, so why drop speed-work altogether? There's also quite a bit of time after the 50k in which you can re-introduce speed sessions.

Hi Intermanaut, I dropped out the speedwork "as a deliberate strategy to avoid overdoing things and injuring myself", as I indicated in my original post - so, when I got a hamstring tendon niggle, for example, I was able to continue upping the mileage by dropping out speedwork. If I'd tried to do speedwork while continuing to increase the mileage, I'd almost certainly have had a full-blown injury develop and needed several weeks off (been there, done that, don't want to repeat). I'm not worrying about my time for the 50K but I would like to be faster for the marathon.

And I was hoping for actual suggestions for speedwork sessions, or a good marathon training plan to follow jumping in part way through, assuming a week of rest then nine weeks to build and taper.

I read your injury-risk thing, but still don't see why you'd not do speed-work for a 50k but would for a 42k.

Of the marathon programmes here you'd be well ahead by the time the 50k is out of the way, so they may be suggesting workouts that are too easy or too slow.

From this sub-3h45 programme, would starting at Week 11 suit you?

http://www.runnersworld.co.uk/racing/rws-garmin-ready-marathon-schedule-sub-345/3181.html

Eitehr double up the weeks or, when you reach the end, start a sub-3h30 programme. Actually, what about starting the sub-3h30 programme at week 6?

Intermanaut: Thanks for the suggestions; I might go for the sub-3:45 program starting at six weeks - not fast enough for the sub 3:30 program!

Re: "still don't see why you'd not do speed-work for a 50k but would for a 42k." I would do speedwork for a 50 K in different circumstances. The difference for these two races is two-fold:

(a) in training for the 50K, I've been increasing my mileage (per week, and length of long runs) substantially, for the first time ever (never previously run longer that 14 or 15 miles; now I'm doing training runs of 26 miles plus). I was also coming back from an injury which had meant no running for four months and really didn't want to repeat that. To increase the mileage safely (i.e. minimise risk of injury), I let the speed drop. Now my legs are used to running the longer distaces and more miles per week, I think it will be safe to start some speedwork. To put it another way, think of the training for the 50K as basework for the marathon.

(b) Different goals. In running the 50K, I'm just interested in completing my first ultra; finishing in 5 to 5.5 hours is fine by me. However, for the marathon in April, I'm more interested in what time I can achieve, as I indicated above. For another 50K, later, I'd be interested in improving my time, so I'd include speedwork (now I can do the mileage okay). But I'm going for a 50M next, so the emphasis will be on safe increase of mileage again!