Lower Back Pain While Running

I'm sat on the sofa feeling very frustrated after attempting 6 x 800m reps as part of my Brighton marathon training, but only managing 2 reps due to lower back pain.

I'm a social runner and have been running 25+ plus miles a week prior to starting the FIRST marathon training plan 3 weeks ago. Everything has been going well and have been feeling confident about the Brighton marathon until the dreaded lower back pain hit me. It first got me on Tuesday evening while doing a 7 mile tempo run but managed to get round at the required pace. I've been out this evening to do my 800m reps and after mile or so I could feel the pain creeping up on me. Managed to do 2 reps and thought I'd be better off getting myself home and logging onto the Runners World forum than attempting the remaining 4 reps in pain. The pain is only there while running, it goes instantly when I walk/sit down etc.

I've had this pain before (around a year ago) but it disappeared after a 6 weeks or so. I can't afford to wait 6 weeks for the pain to go this time as it will severely impact on my marathon training.

Does anyone have ideas as to what the pain could be caused by and how I can reduce/get rid of it? I've read that it may be due to a weak core, if so what are the most effective exercises to build up the core associated with the lower back?

Any advice would be greatly appreciated. 

Thanks for the advice Johnas. I've picked some core strength exercises from the internet which I'll start this evening and will be doing an extensive stretching session before each run. Fingers crossed.

I agree that tight muscles cause strain on the back.  Mine is due to tight hamstrings.

If you want to minimise down time then get a sports massage so that you know exactly what is causing the problem.  They should also be able to tell you which stretches and exercises are good for your specific problem.

Stretch after a run, not before. Warm up is gentle mobilisation of the joints. Stretching is for after, can be hours after even and hold them for 30 -60 seconds,

Tight hip flexors and glutus medius are the most common culprits for 'niggly' low back pain.  Next likely is hamstrings/glut max and rectus femoris muscles.  Best thing would be deep tissue/ sports massage for those.  Next best thing - stretch them!  Weak core will defineatly not help and its a good idea to do those exercises as well - start with basic exercises and slowly increase intensities. 

Hi i have done a similar thing myself and still not any better after 7 months and 3 physios later, l do lumbar exersises and core exersises as the physio told me my core was too weak due to too much running, go and seek medical or physio advice before you do any more damage and cut your mileage back until you seek advice, hope this helps and good luck!!!

I'm in the middle of training for Blackpool marathon and 2 weeks ago my back went (lower back) for no apparent reason. I saw the physio 3 days ago who said I have a weak core as others have said and gave me excercises to strengthen it.

I also in the past have suffered with lower back pain when running but usually when I haven't run for a while and I'm carrying more weight which seems to be the same cause.