Femoral cross-sections with knee loading. (A) Cross-section of the loaded femur with 0.5 N forces at 15 Hz. The section was obtained from the mid-diaphysis. Scale bar = 200 μm. (B) & (C) Double-labeled periosteal surface of the loaded femur. Bright lines represent fluorescent calcein strips. Scale bar = 20 μm. (D) Fluorescence intensity along the line indicated in C. The distance between two lines, 3.8 μm in the diagram, indicates the newly formed bone in 4 days after 3 min loading per day for 3 consecutive days.