I hear this from alot of people that take clen. A friend of mine's whole body gets crampy kinda like when you have the flu. Guess it just depends....some ppl say they feel fine.
I've only taken it once. It was liquid from chemone. After the second week I got strong hamstring and calf cramps especially on leg and back day. I ate a banana in the morning along with potassium and taurine and it became tolerable. The worst side to me was it made my heart feel funny. Not sure if it was irregular heart beat or what. I've read clen is bad on the heart.
I've tried Albuterol -- I didn't experience the "shakes" like I do on clen so it made me feel able to function normally throughout the day. I don't recall cramping but I was loading up on Taurine and Electrolytes...