Doing vs. trying.

OK, let's address your tight hamstrings first. CAUTION: When stretching your chronically tight hamstrings (which directly contributes to your chronic back pain), you must not try hard to stretch them. In fact, you must HARDLY try. If you follow my instruction exactly to the letter, it's probable you won't feel much stretching at all, at least not initially. This is common, so again, DON'T TRY hard to stretch them.

http://www.extensionyoga.com/Pain_Management_4.asp#Sequencing