High dose compressive loads attenuate bone mineral loss in humans with spinal cord injury
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People with spinal cord injury (SCI) lose bone and muscle integrity after their injury. Early doses of stress, applied through electrically induced muscle contractions, preserved bone density at high-risk sites. Appropriately prescribed stress early after the injury may be an important consideration to prevent bone loss after SCI.
Skeletal muscle force can deliver high compressive loads to bones of people with spinal cord injury (SCI). The effective osteogenic dose of load for the distal femur, a chief site of fracture, is unknown. The purpose of this study is to compare three doses of bone compressive loads at the distal femur in individuals with complete SCI who receive a novel stand training intervention.
Seven participants performed unilateral quadriceps stimulation in supported stance [150% body weight (BW) compressive load—“High Dose” while opposite leg received 40% BW—“Low Dose”]. Five participants stood passively without applying quadriceps electrical stimulation to either leg (40% BW load—“Low Dose”). Fifteen participants performed no standing (0% BW load—“Untrained”) and 14 individuals without SCI provided normative data. Participants underwent bone mineral density (BMD) assessment between one and six times over a 3-year training protocol.
BMD for the High Dose group significantly exceeded BMD for both the Low Dose and the Untrained groups (p < 0.05). No significant difference existed between the Low Dose and Untrained groups (p > 0.05), indicating that BMD for participants performing passive stance did not differ from individuals who performed no standing. High-resolution CT imaging of one High Dose participant revealed 86% higher BMD and 67% higher trabecular width in the High Dose limb.
Over 3 years of training, 150% BW compressive load in upright stance significantly attenuated BMD decline when compared to passive standing or to no standing. High-resolution CT indicated that trabecular architecture was preserved by the 150% BW dose of load.
KeywordsBone density Electrical stimulation Muscle physiology Quadriceps femoris Spinal cord injury Weight-bearing strengthening program
This study was supported by awards from the National Institutes of Health (R01NR010285, R01HD062507), the United States Department of Veterans Affairs, the Craig H. Neilsen Foundation, and by the Christopher Reeve Paralysis Foundation. The authors gratefully acknowledge the assistance of Andrew Littman PT, MA; Colleen McHenry MSE, Jason Wu MSE; Shih-Chiao Tseng PhD, PT; Elizabeth Faidley; Brandon Campbell; Deanna Frei, RT (R)(CT)(BD)(CBDT); April Miller, RTR; and Jered Sieren, BSRT(R) MR CT.
Conflicts of interest
The University of Iowa and Dr. Shields have intellectual property covered by a patent for technology used in this investigation.
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