title: Increased osteogenic response to exercise in metaphyseal versus diaphyseal cortical bone.
abstract: Recent experimental data suggest that the anabolic response of bone to changes in physical activity and mechanical loading may vary among different skeletal elements, and even within different regions of the same bone. In order to better understand site-specific variation in bone modeling we used an experimental protocol in which locomotor activity was increased in laboratory mice with regular treadmill exercise for only 30 min/day. We predicted that the regular muscle contractions that occur during exercise would significantly increase cortical bone formation in these animals, and that the increase in cortical bone mass would vary between metaphyseal and diaphyseal regions. Cortical bone mass, density, and bone geometry were compared between these two regions using pQCT technology. Results indicate that exercise increases bone mineral content (BMC) in the mid-diaphysis by approximately 20%, whereas bone mass in the metaphyseal region is increased by approximately 35%. Endosteal and periosteal circumference at the midshaft are increased with exercise, whereas increased periosteal circumference is accompanied by marked endosteal contraction at the metaphysis, resulting in an increase in cortical area of more than 50%. These findings suggest that the osteogenic response of cortical bone to exercise varies significantly along the length of a bone, and more distal regions appear most likely to exhibit morphologic changes when loading conditions are altered.
authors.affiliation: Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta, GA 30912, USA. mhamrick@mail.mcg.edu
authors.forename: M W
authors.initials: MW
authors.lastname: Hamrick
authors.forename: J G
authors.initials: JG
authors.lastname: Skedros
authors.forename: C
authors.initials: C
authors.lastname: Pennington
authors.forename: P L
authors.initials: PL
authors.lastname: McNeil
mesh_terms: D000818:Animals; D015519:Bone Density; D016723:Bone Remodeling / Q000502:physiology*; D001842:Bone and Bones / Q000000981:diagnostic imaging / Q000502:physiology*; D018483:Diaphyses / Q000000981:diagnostic imaging / Q000502:physiology; D005260:Female; D051379:Mice; D018482:Muscle, Skeletal / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000502:physiology*; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed