UKC

So I have been training well until 4 weeks ago when I fell and cracked a rib. Since then I have managed very little running and only a few hilly walks

This weekend I am going to do Ultra Tour Snowdon 50m and I'm wondering how much fitness I would have lost in the four weeks since I cracked my rib?

Sounds like a very long taper as long as you are sound now. Not ideal, but probably not the end of the world either if you were doing well up to that point. I suspect the biggest thing will be the psychological effect of not having run for a month rather than a 15-20% fall in fitness (guess by the way).

I agree, 3-4 weeks isn't a huge amount of time.

You'll feel worse but if you had a big base it's not that long. You'd lose speed quicker than you lose stamina so for a 50mile race I doubt it will have that much impact to be honest. If it was a 5k race I think you'd be significantly slower. In a 50 there's so much else to manage and go wrong, actual fitness is just one component and with a solid base that's not that long away.

Not a lot I suspect.  I've been doing very little running since February due to an injury, and did the MK Half this weekend (as a bit of a test if I was properly recovered or not, and so as not to lose the money ) and came in just under 2hrs which is my pretty consistent half time.

You'll be reet.

First few Kms will be like 'whats this again?' then you'll be fine  

How did you get on? Unforgiving course but it was a cracking day for a long outing in the hills. 

I don’t think the OP would be keen on a “cracking day”.

I did great (for me). Clearly 4 weeks off really helped

amazing race and I fancy 100 next year. Really recommend the 50 to anyone, tough but brill route