Calf pain

I've been noticing that rite 5 seems to be getting harder and harder- I used to have more problems with shoulder and back strength in this one, but now my calves are the problem.
My muscles feel VERY tight, and stretching is difficult and sometimes painful. It feels like the attachments of my calf muscles to the tendons at the knee is irritated and strained.
Not sure why, especially now!
Anyone got any ideas? Tweet