my point is that whether it measures osteoclast or osteoblast activity is irrelevant, because both decrease during the healing phase of bone. i know it is counterintuitive to think that osteoblast activity decreases during a period of bone formation, but the ratio of osteoclast to osteoblast activity is what is relevant in determining if you have net resorption or formation, and in states of high turnover resorption>formation, and vice versa, so a decline in osteoblast activity ensues when remodeling decreases and you get net new bone laid down because the ratio of clast to blast decreases at least that is my understanding of bone physiology