Lower back pain

Simon430 Posts: 118
edited March 2010 in Health, fitness & training
To be more specific, it's lower back pain, down the left hand side, a bit below the kidneys. It usually comes up around 6 miles into my ride. I've had pain there before but never been this painful, it also seems to numb my left leg aswell. Occurs mostly when I'm standing on the pedals, like climbing a hill, but is also there when I pedal sitting down but not as severe. It seems to come and then go, I can feel it coming on then it's really painful for a couple of minutes but after I've stopped climbing the hill for example the pain seems to die away.

Any suggestions on what's wrong? Any ways of reducing the pain? New saddle? New position of saddle & height?