The purpose of this study was to present a spline-function routine for smoothing film data, and consequently to identify the biokinematic performance parameters of the line in slalom skiing. For this reason 34 world class racers were filmed. The results show several parameters that influence the performance and suggest the various interrelations between these parameters, in particular their cause and effect relationship.
Wolfgang Förg-Rob and Werner Nachbauer
Dieter Heinrich, Martin Mössner, Peter Kaps and Werner Nachbauer
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.
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.
Werner Nachbauer, Peter Kaps, Benno Nigg, Fritz Brunner, Alexander Lutz, Günter Obkircher and Martin Mössner
A video technique to obtain 3-D data in an Alpine skiing competition was investigated. The flight and landing phases of a jump were recorded during the 1994 Olympic combined downhill race. A direct linear transformation (DLT) implementation was applied, which computes the DLT parameters for each video image of each camera separately. As a consequence, one is able to pan and tilt the cameras and zoom the lenses. The problem of distributing control points in the large object space could be solved satisfactorily. The method proved to be suitable for obtaining 3-D data with reasonable accuracy, which is even sufficient for inverse dynamics. The computed resultant knee joint forces and moments compare well with results reported by other authors.
Giuliamarta Bottoni, Philipp Kofler, Anne Theresa Herten, Michael Hasler, Anton Giger and Werner Nachbauer
Knee braces might enhance balance ability by improving joint stabilization or proprioception. We tested the effects of three different knee braces on single-limb balance. There was a significant decrease in the anteroposterior balance ability when participants wore the brace that was described as the most cumbersome or uncomfortable (p = .04). For the other two braces, there was no difference in single-limb balance ability compared with the no brace condition. Comfort and weight of the knee brace might alter somatosensory inputs, which play an important role in balance ability.