Hopefully someone can offer a bit of advice here...
Basically I have no problem in training or during road races. However, when I do a fell race I nearly always end up with a nasty pain in my back. It tends to happen on the left side just below half way up my back (round about the kidney area I think) but has happened on both sides on occasions. It really takes my breath away when it happens and I have to really slow down. When I stop it goes away completely although if I prod my back quite hard I can still feel a pain in the area.
Generally it happens on a downhill and is not so bad on uphills. It seems to be happening more and more - at the weekend it happened on an off-road race which was only 6k long and undulating; definitely not hilly.
A few things which may or may not be relevant:
1. I'm asthmatic;
2. Trainers: I wear Asics Nimbus road shoes and Inov8 Roclite 315 trail/fell shoes;
3. I'm 33, male, 5ft 10in, 11st 8lb!
If anyone can offer any advice on what might be causing this, how to prevent it (other than "don't do fell/off-road races) etc I'd really appreciate it :-)