I play with a Extrem Pro 2.0 and Dunlop 200 both SW in the upper 320s and at least 11.8 strung. A few days ago I tried a Dunlop 400 Tour with a SW of 306 and 11.6. Now I have a aching back for 3 days now. I've never had this before. Could it be the lighter racquet cause I am hesitant to use it again. I could create some great serves with the lighter racquet due to faster RHS.