RESUMO
The gross mechanical efficiency of the manual wheelchair propulsion movement is particularly low compared to other movements. The energy losses in the manual wheelchair propulsion movement are partly due to energy losses associated with the wheelchair, and especially to the rolling resistance of the wheels. The distribution of mass between the front rear wheels and the caster wheels has a significant impact on the rolling resistance. The study of the caster wheels cannot therefore be neglected due to their involvement in rolling resistance. Thus, this study aimed to evaluate the power dissipated due to rolling resistance by different caster wheels, at different speeds and under different loadings on various terrains. Four caster wheels of different shapes, diameters, and materials were tested on two surfaces representative of indoor sports surfaces at four different speeds and under four loadings. The results showed a minimal dissipated power of 0.4±0.2W for the skate caster, on the parquet, at 0.5 m/s and under a loading of 50 N. The maximal mean power dissipated was 43.3±27.6W still for the skate caster, but on the Taraflex, at 1.5 m/s and under loading of 200 N. The power dissipated on the parquet was lower than the one on the Taraflex. The Spherical and Omniwheel caster wheels dissipated less power than the two other casters. This study showed that caster wheels cannot be neglected in the assessment of gross mechanical efficiency, particularly in light of the power dissipated by athletes during propulsion.
Highlights the importance of choosing the right front casters depending on the conditions of use of the manual wheelchair.First study to evaluate power dissipation due to rolling resistance in front casters during wheelchair propulsion.Shows that a Taraflex type floor is not suitable for wheelchair sports performance and injury prevention purposes and lower musculoskeletal constraints with equivalent performance.
RESUMO
STUDY DESIGN: This study analyzed intraoperatively the three-dimensional displacement of vertebrae during rotation of the Cotrel-Dubousset rod for scoliosis correction, using an optoelectronic method. OBJECTIVE: To evaluate three-dimensional transitions and rotations of instrumented and uninstrumented vertebrae, produced by the Cotrel-Dubousset instrumentation "derotation" maneuver. SUMMARY OF BACKGROUND DATA: Published reports indicate that Cotrel-Dubousset instrumentation has been more effective in producing spinal derotation than vertebral axial derotation, but no study analyzed intraoperatively the effects on the vertebrae produced solely by rotation of the rod. METHODS: Eight patients with idiopathic scoliosis treated with Cotrel-Dubousset instrumentation underwent intraoperative optoelectronic monitoring using infrared cameras (Vicon). Markers were implanted in the spinous processes of the lower and upper instrumented vertebrae (LIV, UIV), the adjacent uninstrumented vertebrae below and above (-LIV, +UIV), and the apical vertebra. During rod rotation, acquisition and processing of cameras data were performed to obtain three-dimensional displacements of vertebrae. RESULTS: Translations and rotations of LIV and UIV were in identical directions to those of -LIV and +UIV, respectively. Orientation of the LIV hook influenced the displacement of LIV and -LIV. Posterior translation of the apical vertebra was commonly observed in thoracic King II, III, or V curvatures (apical vertebra = T9), and anterior translation in King I and IV and thoracolumbar curvatures (apical vertebra = T11-T12). Axial rotation of the apical vertebra was increased in thoracic curvatures and decreased in thoracolumbar and lumbar curvatures. Lateral translation was the major displacement observed. CONCLUSIONS: Rotation of the rod produces rotational and translational changes along each axis. These results are preliminary, but substantial. Technical improvement would allow more accurate results in the near future.