Improved Bone Structure and Strength After Long-Term Mechanical Loading Is Greatest if Loading Is Separated Into Short Bouts

• DOI: 10.1359/jbmr.2002.17.8.1545
• Publication Date: 2006-04-27T05:31:59Z
• Authors: Alexander G. Robling; Felicia M. Hinant; David B. Burr; Charles H. Turner
• Keywords: Peak load; Mechanical load; Biomechanics

Abstract Mechanical loading presents a potent osteogenic stimulus to bone cells, but cells desensitize rapidly mechanical stimulation. Resensitization must occur before the can transduce future signals effectively. Previous experiments show that protocols are more if load cycles divided into several discrete bouts, separated by hours, than applied in single uninterrupted bout. We investigated effect of bouts on structure and biomechanical properties rat ulna after 16 weeks loading. The right ulnas 26 adult female rats were subjected 360 cycles/day, delivered haversine waveform at 17 N peak force, 3 days/week for weeks. One-half animals (n = 13) administered all daily bout (360 × 1); other half 90 four times per day (90 4), with h between bouts. A nonloaded baseline control (BLC) group an age-matched (AMC) 9/group) included experiment. following measurements collected death: situ strain midshaft; ulnar length; maximum minimum second moments area (IMAX IMIN) along entire length (1-mm increments); ultimate energy failure, stiffness whole ulnas. Qualitative observations morphology made from images reconstructed microcomputed tomography (μCT) slices. Loading according 1 4 schedules improved force 64% 87%, failure 94% 165%, IMAX 13% 26% (in middistal diaphysis), IMIN 69% 96% reduced 40% 36%, respectively. large increases occurred despite very low 5–12% gains areal mineral density (aBMD) content (BMC). is effective enhancing structural loads recovery periods schedule), session 1). Modest aBMD BMC improve substantially new formation localized most biomechanically relevant sites, as occurs during load-induced formation.