Training advice for double marathon (with cross training)

I'm loosely planning to run the London Marathon backwards then forwards next April. Starting first thing and running the course back to front, then turning around and running it forwards with the runners/event itself.

I've completed 4 marathons, plenty of halfs and a fair bit of adventure racing. Best Marathon time 3:26. I'd like to get advice from people on a few things:

1. What sort of time should I be aiming for first time round. My baseline is to complete but, being a bit competitive with myself, I'd like to set myself a target as a challenge. I'm guessing about 8 hours or so.

2. I cycle to work most of the time (16 miles per working day) and want to factor this into my training. Has anyone got experience of using a high level of cross training in their ultra-marathon schedule. My marathon training is usually sprints tuesday, tempo on thursday, long run on Sunday (the FIRST insititute three day schedule). Bike most of the other weekdays and rest saturday. Any advice or experience to share would be valuable.

3. Any hints on the turnaround? I'm assuming I'll have a slight break between the back/forwards section. I want to use that time effectively if I have it. I'm assuming a good feed on something I've run on before in training and just keep it loose.

4. Anyone else planning doing this?
Thanks all

Ok, nto too sure on the cross training side of the things but for your other points :

1) Your 2nd half is near enough guaranteed to be slower. Bear that in mind when you think of putting a target time on it for yourself. Based on your marathon PB sub 8 hours will be a very tough target in my opinion, but whos to say it is not possible? I would say definitely out of reach if you are not stopping the clock between arriving at the end of your first leg and setting off again though as you are going to lose time getting in to your pen, moving to the start line etc

3) I am not sure how strict they would be on you running over the startline area from the wrong direction, in fact would it be at all possible? if no, what is the route you plan to get to your pen? Will someone be there waiting for you with food etc? If you have time then a some good food and drink, keep moving, some gentle stretches and maybe a change of kit?

Thanks r.e. Time, think I will probably stop my own timer. I'll get elapsed time from the garmin report anyway.

I'm going to have a chat with the Marathon organisers as I know people have done this before. So there will certainly be some logistics to deal with in terms of start of reverse section, getting into pens at start of forward section. I'm only expecting them to time the forward section, naturally, so I imagine I can be creative with the start point if needed.

Good point r.e. having someone to meet with food and clothes. Definitely necessary.

Ok, well if you stop your timer and then add the chip time from your forward effort then 8 hours will be tough but not impossible.

Good idea, I was just thinking that obviously it is a closed course and they don't let anyone forward of the pens so would need to arrange a route into your start area.

If someone is meeting you then food, drink, stretch, don't sit down for longer than it takes to change shoes etc, change kit. Sorted.

I, and others I know, do a fair bit of cycling very similar to you. If I am not running to work then I bike it which is about a 60km round trip

The key is to spin rather than push a heavy gear

Long bikes every now and again can really give your legs a good shake up

Look out for insufficient Garmin battery life!

If your commute is 16 miles/ day- why not run it regularly? Better training than cycling it.

Come over to the wannabe ultra runner thread.

I would say you want to test what happens with the break.

I have done triathlons Swim-Bike-Run all relatively OK
I have done duathlons - Run-Bike-Run Horrific cramp infested changeovers on both transitions.

Why the difference I don't know but running before a bike kills my calves.

Equally you need to work out what happens if you run 26 miles then stop for 30-minutes or 1-hour or 1-30 and then go again. You don't need a long second run, just need to see what happens on the first few miles. So you could try 13-miles then home rested, fuelled and out the door again 1-hour later. Get the body used to this unnecessary abuse.

Biking generally has a good cross over to running. I use FIRST for all marathons I have trained for. But would also suggest ou build in some double training runs e.g. Sunday evening Monday morning (if you need Saturday for family commitments)

A 3:26 single to an 8-hour double seems a tough leap. How are you going to achieve the improvements? Weightloss (would help me), improved fitness, more scientific training? Although if you have been using first sounds like you haven't been just doing the run till drop plan.

Logistics at the break for food and warmth will also be important. Getting cold could cause issues.

Hope this helps