I have a double prolapsed disc in my lumbar spine, along with two dehydrated discs, and I experienced symptoms similar to you, where my back would literally lock up, and I couldnt get my hands past my knees. This resulted in my running about 0.1-0.2 slower than I was capable, mostly because I couldnt start very well as it hurt!
Since it has been diagnosed, I have done a lot of specific core work, focusing on been able to control rotational torque, as well as regular spinal manipulations and deep-tissue massage.
Hope that helps!