I have the same pains when taking 500mg of sust, i get it because i have a bad back and the sust tightens all of my muscles up, including the back of the legs and lower back. to releave the pain........stretch often. plus at night take a muscle relaxer and during the day take some type of antiflammorary. (mobic) the doctor prescrided it to me and within 2 days, no more pain.
paulie