I've developed a stress fracture in my right leg. What this means is though I can't really feel or see it (can feel pain upon heavy loading - running), my leg is technically fractured and I'm not supposed to load it. This is a rather pain in the ass in terms of fitness and strength. I'm planning on increasing my swimming significantly, but I'm at a rather loss for what to do regarding core strength. I was primarily doing plank varieties, bicycle crunches and some push-up lat rows, but now all but the crunches are off limits for me. Does anyone know of any core exercises that do not load up the lower legs in any way?