OK guys ive had on and off back pain. nothing big, just really annoying. i recently remembered that this started when i switched to half poly half synthtic a year ago. they normally last 3 months for me. they go really dead after about 2 months, but i never have cut them out before. recently the back pain has been especially bad. i was in the third month of one racquet. on a hunch, i switched to my other one which had a brand new stringjob. the next day, i hit hard and full for 2 hrs and no back pain!!! i am so happy i finally found the cause of my back pain. i blamed it on everything from basketball, housework, clarinet, and technique. can anyone confirm this? can dead polys cause injuries?????