This article presents a study of torsion stiffness of a specific racing cross-country ski boot for the skating technique conducted by means of numerical analyses and measurements. Its aim is to determine relative torsion stiffness contributions, relative mass contributions, and the ratios between them (torsion stiffness/mass ratios) for individual boot components of the torsionally most deformable part of the boot. These are basic data for torsion stiffness-mass optimization of the boot. For acquiring these data, a complex finite element model of the cross-country ski boot and an artificial silicone foot were created in different versions after an existing device designed for measurement of stiffness properties of the boots. Material properties employed in the model were acquired experimentally. The confirmed model was used for determination of the torsion deformation contributions of different regions of the boot. Focus was given to the middle region, whose contribution is the largest. The aforementioned data were determined for individual boot components of this region. The soles, which contribute the most to the middle region's torsion stiffness, turned out to have the highest potential for torsion stiffness-mass optimization, because of their lowest torsion stiffness/mass ratio and highest mass contribution. The shoe-upper has the highest torsion stiffness/mass ratio and is, therefore, the most worthwhile to be enlarged. The torsion stiffness/mass ratio of the strengthening bands is lower than expected and could likely be increased by their positioning.

For greater energy efficiency of sports footwear, mass needs to be minimized while preserving other favourable characteristics. In this article, an analysis of the flexion stiffness of the foot region, precisely its middle region, of a specific racing cross-country ski boot for the skating technique regarding its mass was performed. On the basis of a complex finite element model of the ski boot and an existing boot stiffness measuring set-up, flexion stiffness portions, mass portions and flexion stiffness/mass portion ratios were determined for individual boot components regarding the middle boot region. These values were determined for the shoe-upper with strengthening bands and shoelaces (altogether S-U), the sole, the midsole and the glue layer between. The S-U turned out to contribute a high flexion stiffness portion to the boot's middle region's flexion stiffness and also its flexion stiffness/mass portion ratio turned out to be the highest. The midsole and the sole present the highest potential for flexion stiffness/mass optimization due to their lowest flexion stiffness/mass ratios and highest mass portions. In order to increase the flexion stiffness/mass ratio of the middle boot region, the sole's and the midsole's size portions should be reduced, while the S-U's size portion should be increased. Beside these findings, other suggestions in order to increase the flexion stiffness/mass ratio of the boot's middle region are also given.

No abstract

For a detailed biomechanical analysis of roller-ski skating a precise measurement of ground reaction forces is needed in addition to the measurement of the kinematic parameters. An innovative portable force measuring system was developed from processed roller-skis and ski poles equipped with strain gauges. The measuring system can measure normal (with respect to the upper surface of the roller-ski) and transverse forces (in the axial direction of the wheel) on each wheel, and axial forces in the ski poles. Force sensors are connected by cables to the data acquisition system carried in a backpack by the runner. In case of terrain usage, also a portable computer and a power supply are carried in the backpack. Calibration procedure for this measurement system is presented and measurement uncertainty of the sensors is calculated. The estimated measurement uncertainty of the entire measuring chain of individual roller-ski sensor, at a confidence level of 95 %, is up to ± 2,34 % of the maximum calibration forces. For the sensors of the poles this value makes up to ± 1,47 % of the maximum calibration force. Sample data from a roller-ski skating trial on a treadmill is presented and interpreted.

This case study examines the impact of boot longitudinal flexural stiffness on the total external mechanical work of a skier’s centre of mass per distance travelled in the forward direction ([Formula: see text] EX (J/m)) and on running economy during skate roller-skiing under submaximal steady-state conditions. Moreover, it analyses time derivatives of total W EX, of W EX performed by the roller-skis and poles, respectively, and of the directly useful mechanical work (the sum of the work to overcome centre of mass’ gravity and rolling resistance) within a typical roller-skiing cycle. Multiple roller-skiing trials (G3 technique) were performed by one subject on an inclined treadmill with boots of soft, intermediate, and stiff flexural stiffness. The orientation and magnitude of the roller-ski and pole ground reaction forces, body kinematics, VO2, and lactic acid concentration were monitored. The stiff boots had 13.4% ( p < 0.01) lower [Formula: see text] EX compared to the intermediate boots, and 20.7% ( p < 0.001) lower [Formula: see text] EX compared to the soft boots. Regarding running economy, the soft boots had 2.2% ( p < 0.05) higher VO2 compared to the intermediate boots, but the same VO2 compared to the stiff boots. In conclusion, the soft boots had significantly higher [Formula: see text] EX and running economy, while stiff boots had significantly lower [Formula: see text] EX and intermediate boots significantly lower running economy. Moreover, [Formula: see text] EX appears to be a better indicator of the boot flexural stiffness impact on energy efficiency than running economy.