Low‐Magnitude Mechanical Loading Becomes Osteogenic When Rest Is Inserted Between Each Load Cycle

• Published in: Journal of bone and mineral research Vol. 17; no. 9; pp. 1613 - 1620
• Main Authors: Srinivasan, Sundar, Weimer, David A., Agans, Steven C., Bain, Steven D., Gross, Ted S.
• Format: Journal Article
• Language: English
• Published: Washington, DC John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR) 01.09.2002; American Society for Bone and Mineral Research
• Subjects: Animals; Biological and medical sciences; Biomechanical Phenomena; bone mass; Bone Remodeling - physiology; exercise; Female; Fundamental and applied biological sciences. Psychology; Male; mechanotransduction; Mice; Mice, Inbred C57BL; osteoblast; Osteoblasts - physiology; Osteogenesis - physiology; osteogenic; Physical Exertion - physiology; Skeleton and joints; Space life sciences; Stress, Mechanical; Tibia - anatomy & histology; Tibia - physiology; Time Factors; Turkeys; Ulna - anatomy & histology; Ulna - physiology; Vertebrates: osteoarticular system, musculoskeletal system; Physical exercise; Ulna; Rodentia; Environmental factor; Ossification; Osteoarticular system; Biomechanics; Vertebrata; Rest; Mammalia; Bone mass; Mouse; Tibia; Animal; Osteoblast; Mechanotransduction; Bone; Aves; Loading test(mechanics); Meleagris gallopavo; Adaptation
• ISSN: 0884-0431; 1523-4681
• DOI: 10.1359/jbmr.2002.17.9.1613

Strategies to counteract bone loss with exercise have had fairly limited success, particularly those regimens subjecting the skeleton to mild activity such as walking. In contrast, here we show that it is possible to induce substantial bone formation with low‐magnitude loading. In two distinct in vivo models of bone adaptation, we found that insertion of a 10‐s rest interval between each load cycle transformed a locomotion‐like loading regime that minimally influenced osteoblast activity into a potent anabolic stimulus. In the avian ulna model, the minimal mean (+SE) periosteal labeled surface (Ps.LS) observed in the intact contralateral bones (1.6 ± 1.5%) was doubled after 3 consecutive days of low‐magnitude loading (3.8 ± 1.5%; p = 0.03). However, modifying the regimen by inserting 10 s of rest between each load cycle significantly enhanced the periosteal response (21.9 + 4.5%; p = 0.03). In the murine tibia model, 5 consecutive days of 100 low‐magnitude loading cycles did not significantly alter mean periosteal bone formation rate (BFR) compared with contralateral bones (0.011 ± 0.005 μm3/μm2 per day vs. 0.021 ± 0.013 μm3/μm2 per day). In contrast, separating each of 10 of the same loading cycles with 10 s of rest significantly elevated periosteal BFR (0.167 ± 0.049 μm3/μm2 per day; p = 0.01). Endocortical bone formation parameters were not altered by any loading regimen in either model. We conclude that 10 s of rest between each load cycle of a low‐magnitude loading protocol greatly enhances the osteogenic potential of the regimen.