ORIGINAL RESEARCH The Effect of Level and Downhill Running on Cortical and Trabecular Bone in Growing Rats Nina Hamann • Thomas Kohler • Ralph Mu ¨ller • Gert-Peter Bru ¨ ggemann • Anja Niehoff Received: 12 January 2012 / Accepted: 6 March 2012 / Published online: 1 April 2012 Ó Springer Science+Business Media, LLC 2012 Abstract Mechanical loading is essential for bone development and prevention of age-related bone diseases. Muscular contractions during physical activity and the generated strain magnitude are primary determinants for the osteogenic response. However, the adaptation capacity of bones, especially due to different muscle contraction types, is largely unknown. In the present study we exam- ined the effect of different running modes characterized by different muscle contraction types and loading patterns on the morphological, structural, and mechanical properties of different sites in the femur of growing rats. Thirty-six female Sprague-Dawley rats were randomly assigned to a nonactive age-matched control (AMC), a level running (LEVEL), and a 20° decline downhill running (DOWN) group (n = 12 each). Running groups were trained on a treadmill for 30 min/day, 5 days/week for 6 weeks. After death, pQCT analysis of the meta- and diaphyses, micro- CT analysis of the epiphysis, and mechanical testing of the femur were performed. The Tb.BMD in the metaphysis was significantly (P \ 0.05) increased in the DOWN compared to the AMC group, whereas level running had no effect on Tb.BMD. While Young’s modulus was signifi- cantly different (P \ 0.05) between the DOWN and LEVEL groups, no structural alterations were found in the diaphysis between the groups. Further, subchondral tra- becular bone did not show exercise-induced changes caused by the different running modes but displayed a remarkably high intraepiphyseal variability. Downhill running seems to be a potent osteogenic stimulus in the femoral metaphysis. Keywords Running exercise Á Eccentric Á Concentric Á Muscle contraction Á Mechanical property Mechanical loading and the resulting stresses and strains generated through physical activity play an important role in the development and maintenance of bone. It is gener- ally accepted that exercise during tissue maturation con- tributes to an increased peak bone density and bone mass that is even beneficial in later age, protecting against age- related bone diseases such as osteopenia and osteoporosis [1]. Even though a number of studies have investigated the effect of physical activity on bone properties and metabo- lism, they allow only limited conclusions about the exact relationship between exercise and bone response. Artificial loading by external bone stimulation in animal studies demonstrated that dynamic strain is more effective than static strain [2], while strain magnitude correlates with the increase of bone mass [3]. Furthermore, a high rate of T. Kohler and R. Mu ¨ller own stock and R. Mu ¨ller has consultant/ advisory role to b-cube AG. All other authors have stated that they have no conflict of interest. N. Hamann Á G.-P. Bru ¨ggemann Á A. Niehoff (&) Institute of Biomechanics and Orthopedics, German Sport University Cologne, Am Sportpark Mu ¨ngersdorf 6, 50933 Cologne, Germany e-mail: niehoff@dshs-koeln.de N. Hamann e-mail: hamann@dshs-koeln.de G.-P. Bru ¨ggemann e-mail: brueggemann@dshs-koeln.de T. Kohler b-cube, Schlieren-Zurich, Switzerland e-mail: thkohler@b-cube.ch R. Mu ¨ller Institute for Biomechanics, ETH Zu ¨rich, Zurich, Switzerland e-mail: ram@ethz.ch 123 Calcif Tissue Int (2012) 90:429–437 DOI 10.1007/s00223-012-9593-6