There is plenty of conflicting information on the benefits of cross training for runners.  Some say that the only thing that will help improve running times is pure running itself, but others believe that cross training will have a positive effect.  

A year ago, (after 14 years of  running being my only serious exercise),  I started adding some cross training to my weekly exercise routine  i.e. some  cycling - although a bit erratic - and a weekly circuit training class (including core work).  Subsequently  I have  found that my race pace has improved (and being over 40 this seems to be bucking the trend). So, can only conclude that the cross training has been an important part in my imporovement.   Of course, adding extra exercise has also resulted in a a bit of weight loss, so that may be a factor as well.

Has anyone else had a similar experience?  Do you think core work is particularly important or does any type of cross training help?  Has anyone tried this and it hasn't made any difference?

I'm sure gyms are great if you are going to get enough use out of them.  But, as running is still the bulk of my exercise routine I don't think I would, so to get my cross training (and particularly core work which is recommended by a lot of runners)  I started going along to a weekly circuit training class at my local village hall which seems to have done the trick.   If you are self motivated enough it is completely possible to do this  at home without specialist equipment.  I have also taken to cycling where I can rather than taking the car on short journeys (very satisfying to feel environmentally friendly as well!)

I discovered cross training in a big way this year and it has helped my running. I started cycling as part of my journey to work & dropped the gym to pay for the new bike. It has been great and helped me to run well even in weeks when I was lazy with my running. I highly recommend it!