I'm pretty active and cardio fit, I'm a long runner and I do bootcamp/meta fit/ run club 3-4 times a week, I'm not new to exercise. But every time I do a sit up/leg raise/ bicycle crunch etc, (eg any ab/core work) my whole lower bank is crunching away. Is this technique related? Is it going to eventually damage me? Can I train it out? It doesn't hurt at all, but the clunk goes right through me with every rep! Any advice??