The Effect Of Robotic Gait Training On Spinal Cord Transected Rat Femurs

Abstract

Robotic locomotor training has been shown to be effective for significantly improving body composition and making some moderate, but not significant, changes in bone mineral density in individuals with spinal cord injury (Karalis et al., 2017). The effect of the training on other important mechanical properties of bone is unknown. PURPOSE: To determine the effects of 8 weeks of robotic locomotor training on mechanical properties of rat bones. METHODS: Twelve female Sprague-Dawley rats received spinal cord transections at 5 days old. At 3 weeks old, half of them were randomly assigned to a Training group and half to a Control group. The Training group received 5 minutes of robotic gait training with 90% body support for 5 days a week for 8 weeks. The Control group received no exercise. At the conclusion of the 8 weeks, the animals were euthanized and the right femurs were harvested for testing. Anthropometric measures and 3-point bending tests using an Instron material testing system (Norwood, MA) were performed. Independent t-tests were used to determine differences between the two groups (p < 0.05). RESULTS: There was no difference in body mass between the two groups prior to group assignments, but after 6 weeks of training the Control group had greater mass (p = 0.035) and at the end of training this difference continued (mass = 210.3 ± 36.0 g vs. 166.7 ± 14.5 g; p = 0.012). The Control group’s femur mass was significantly larger (p = 0.041), but when considered as a percentage of body mass, the Training group’s femur mass was larger (p = 0.014). Peak load and rupture loads were not different between the two groups, but when normalized for body mass the Training group had larger load values than the Control group (59.0±2.7% and 53.3±12.1% for the Training and 52.4±2.0% and 41.6±8.7% for Control; p = 0.001 and p = 0.035, respectively). The deflection at rupture was greater for the Control group (0.75 ± 0.09 mm vs. 0.59 ± 0.14 mm; p = 0.025), as was the energy absorbed (57.0 ± 6.1 mJ vs. 39.6 ± 12.1 mJ; p = 0.009). There were some differences in midshaft diameters, but the cross-sectional areas were not different between the two groups. CONCLUSION: Rats who experienced training had stronger and more massive femurs than those who experienced no training. This work was supported by NSF 0850516.