Using a cyclic strain unit,the proliferation and differentiation in rat osteoblasts that underwent mechanical strain were studied.Cells were subjected to 15% elongation at frequency 20 cycles/min at several loading times.Under the action of different loading time,the relative proliferation index of osteoblasts at the 12h of loading time was the biggest,and it gradually tended toward 1 with the increase of the loading time.The relative ALP activity index of osteoblasts increased significantly after being loa...