title: Effects of running on the torsional strength, morphometry, and bone mass of the rat skeleton.
abstract: Intensity and duration effects of weight-bearing exercise on the rat skeleton were investigated. Eighty-four 3-month-old female Sprague-Dawley rats were assigned to control and nine exercise groups. Exercised rats were run on a treadmill for either 30, 60, or 90 min.d-1 at low (Vo2max approximately 55%), medium (VO2max approximately 65%), or high (VO2max approximately 75%) intensity 4 d.wk-1 for 10 wk. Rat femurs, tibias, and vertebrae were harvested for torsional mechanical tests, bone density assessment, and morphometry. Our results indicate exercise has a significant effect (P < 0.05) on the femoral mechanical response (energy absorbed and twist angle), tibial morphometry (cortical bone area and thickness), and tibial and vertebral bone density measurements but had no effect (P > 0.05) on bone strength when compared with control values. Higher intensity exercise decreased tibial and femoral torque (P < 0.05). Long duration exercise increased tibial and femoral stiffness and decreased twist angle and energy absorbed (P < 0.05). These results indicate bone adapts to its loading environment by increasing bone mineral density, increasing cortical bone area, increasing stiffness, decreasing energy absorbed, and decreasing twist angle. High-intensity exercise decreased the maximum force the bone could withstand, whereas long duration exercise made the bone more brittle.
authors.affiliation: Division of Orthopaedics, School of Medicine, Oregon Health Sciences University, Portland, USA.
authors.forename: D L
authors.initials: DL
authors.lastname: Wheeler
authors.forename: J E
authors.initials: JE
authors.lastname: Graves
authors.forename: G J
authors.initials: GJ
authors.lastname: Miller
authors.forename: R E
authors.initials: RE
authors.lastname: Vander Griend
authors.forename: T J
authors.initials: TJ
authors.lastname: Wronski
authors.forename: S K
authors.initials: SK
authors.lastname: Powers
authors.forename: H M
authors.initials: HM
authors.lastname: Park
mesh_terms: D015502:Absorptiometry, Photon; D000818:Animals; D001696:Biomechanical Phenomena; D015519:Bone Density; D001842:Bone and Bones / Q000033:anatomy & histology / Q000502:physiology*; D005260:Female; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley