Isokinetic Resistance Training Increases Tibial Bending Stiffness in Young Women Larry E. Miller Æ Sharon M. Nickols-Richardson Æ David F. Wootten Æ Warren K. Ramp Æ Charles R. Steele Æ John R. Cotton Æ James P. Carneal Æ William G. Herbert Received: 4 December 2008 / Accepted: 31 March 2009 / Published online: 1 May 2009 Ó Springer Science+Business Media, LLC 2009 Abstract Bone mineral content (BMC) and bone mineral density (BMD) are common but imperfect surrogate mea- sures of bone strength. The mechanical response tissue analyzer is a device that measures long bone bending stiffness (EI), which strongly predicts bone breaking strength. We hypothesized that isokinetic resistance train- ing of the knee flexor and extensor muscles would increase tibial EI, BMC, and BMD in young women. Fifty-two women, aged 18–26 years, performed concentric (CON, n = 30) or eccentric (ECC, n = 22) isokinetic resistance training with the nondominant leg three times per week for 20 weeks. Before and after the training period, subjects were tested for CON and ECC peak torque of the knee flexor and extensor muscles with isokinetic dynamometry, tibial BMC and BMD using dual-energy X-ray absorpti- ometry, and tibial EI using mechanical response tissue analysis. Both training groups increased CON (15–21%) and ECC (17–31%) peak torque vs. the untrained leg. Tibial EI increased in the entire cohort (26%) and in each training group (CON 34%, ECC 16%) vs. the untrained tibia. Tibial BMC and BMD increased in the trained and untrained tibiae, with no significant differences between limbs. No differential tibial EI or bone mineral outcomes were observed between the CON and ECC training groups. In summary, CON and ECC isokinetic resistance training increased tibial EI, but not BMC or BMD, in young women. Keywords Bending stiffness Á Bone mineral Á Isokinetic Á Mechanical response tissue analyzer Á Women Bone mineral content (BMC) and bone mineral density (BMD) measured with dual-energy X-ray absorptiome- try (DXA) are common surrogate measures of bone strength and fracture risk. However, DXA has known limitations, including radiation exposure, high expense, slow scan times, and lack of portability. Furthermore, fracture risk prediction based on bone mineral alone is imperfect. Most patients who suffer hip fractures are not osteoporotic [1]. Antiresorptive therapy slightly L. E. Miller Á D. F. Wootten Á W. G. Herbert Department of Human Nutrition, Foods and Exercise, Virginia Polytechnic Institute and State University, 213 War Memorial Hall, Blacksburg, VA 24061, USA S. M. Nickols-Richardson Department of Nutritional Sciences, Pennsylvania State University, 323 Chandlee Laboratory, University Park, PA 16802, USA W. K. Ramp Á W. G. Herbert Health Research Group, LLC, P.O. Box 146, Rockbridge Baths, VA 24473, USA C. R. Steele Department of Mechanical Engineering, Stanford University, Building 530, 440 Escondido Mall, Stanford, CA 94305, USA J. R. Cotton Department of Mechanical Engineering, Ohio University, 247 Stocker Center, Athens, OH 45701, USA J. P. Carneal Vibration and Acoustics Laboratories, Virginia Polytechnic Institute and State University, 147 Durham Hall, Blacksburg, VA 24061, USA L. E. Miller (&) 1786 Ax Handle Way, Flagstaff, AZ 86001, USA e-mail: millerle@vt.edu 123 Calcif Tissue Int (2009) 84:446–452 DOI 10.1007/s00223-009-9247-5