Posted: 09/09/2014 at 12:36
Hi MikeyGiggs, first thing is: don't panic!
I'm the opposite of you - as a long time outdoors runner, I struggle on the rare occasions I use a treadmill. The fitness you built on the treadmill will benefit your outdoor running, but it just takes a little time to adapt to the "road" not moving underneath you.
Cardiff is a big event and you'll find a lot of people who are covering the distance for the first time, and many who haven't done as much training as you.
As there's only four weeks to go, you are not going to make any dramatic fitness improvements in this time. However, by trying to do too much you can still ruin your chances of participating in the event.
For example, you mention running twice per day which is normally something done by very experienced runners to add additional mileage. The old rule is not to add more than 10% distance per week, as going above this leads to fatigue and increased risk of injury.
You would be better working out a coping strategy for covering the distance, such as a run-walk routine like 10 mins run followed by 2 mins walk and getting used to this routine. You can gradually build the time/distance of this over the next two or three weeks, and then make sure you take the week or two before the event a lot easier (roughly 50% of the distance covered in your last full week of training). This is referred to as the taper period and lets you rest and recover before the race.
Hopefully, you'll be at the start line fit & healthy and raring to go (as there will be many who won't!). Cardiff is a great event and the crowd is big enough to give you a boost, so I'm sure you'll enjoy it.