I do reformer pilates regularly. I didn't have a calf injury specifically, it's just that I run in a way that puts more force through the calves so without a slow and proper build-up after a break I do risk soreness/injury in them (which obviously means less time running). The actual injury is just the ongoing after effects of a meniscus tear I had a few years ago. Unfortunately, it can unexpectedly flare up again from time to time and I need to rest the knee until it settles down.