The deformation of skis and the contact pressure between skis and snow are crucial factors for carved turns in alpine skiing. The purpose of the current study was to develop and to evaluate an optimization method to determine the bending and torsional stiffness that lead to a given bending and torsional deflection of the ski. Euler-Bernoulli beam theory and classical torsion theory were applied to model the deformation of the ski. Bending and torsional stiffness were approximated as linear combinations of B-splines. To compute the unknown coefficients, a parameter optimization problem was formulated and successfully solved by multiple shooting and least squares data fitting. The proposed optimization method was evaluated based on ski stiffness data and ski deformation data taken from a recently published simulation study. The ski deformation data were used as input data to the optimization method. The optimization method was capable of successfully reproducing the shape of the original bending and torsional stiffness data of the ski with a root mean square error below 1 N m2. In conclusion, the proposed computational method offers the possibility to calculate ski stiffness properties with respect to a given ski deformation.
Dieter Heinrich, Martin Mössner, Peter Kaps and Werner Nachbauer
Giuliamarta Bottoni, Dieter Heinrich, Philipp Kofler, Michael Hasler and Werner Nachbauer
During sport activity, knee proprioception might worsen. This decrease in proprioceptive acuity negatively influences motor control and therefore may increase injury risk. Hiking is a common activity characterized by a higher-intensity-exercise phase during uphill walking and a lower-intensity-exercise phase during downhill walking. Pain and injuries are reported in hiking, especially during the downhill phase.
To examine the effect of a hiking-fatigue protocol on joint-position sense.
University research laboratory.
24 nonprofessional sportswomen without knee injuries.
Main Outcome Measures:
Joint-position sense was tested at the beginning, after 30 min uphill walking, and after 30 min downhill walking on a treadmill (continuous protocol).
After downhill walking, joint-position sense was significantly worse than in the test at the beginning (P = .035, α = .05). After uphill walking, no differences were observed in comparison with the test at the beginning (P = .172, α = .05) or the test after downhill walking (P = .165, α = .05).
Downhill walking causes impairment in knee-joint-position sense. Considering these results, injury-prevention protocols for hiking should focus on maintaining and improving knee proprioception during the descending phase.