Wednesday was my second go at FSs and those calf raises just killed me. I was about 20 reps in when I started to cramp up. The other calf raise variations were event worse (bad hip flexor mobility...SO bad).
Now, two days later, I still wince with every step and have to hold the handrail going up and down stairs. Looking around the forum, the calf raises have something of a reputation for doing this. I'm pretty sure no permanent damage was done and within a few days the DOMS will have passed, but it's pretty ferocious right now and, well, I just felt like sharing :-)