| 1. |
- Ainegren, Mats, et al.
(författare)
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An experimental study to compare the grip of classical style roller skis with on-snow skiing
- 2013
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Ingår i: Sports Engineering. - : Springer Science and Business Media LLC. - 1369-7072 .- 1460-2687. ; 16:2, s. 115-122
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Tidskriftsartikel (refereegranskat)abstract
- Cross-country skiers use roller skis for their snow-free training with the aim of imitating skiing on snow. Also, exercise laboratories evaluate the biomechanics and physiology of cross-country skiing using roller skis on a treadmill. The roller skis on the market that are constructed for use in the classical style are equipped with a front and a back wheel, one of which has a ratchet to enable it to grip the surface when diagonal striding and kick double poling (static friction). The aim of this study was to investigate static friction coefficients (μS) of ratcheted wheel roller skis, and compare the results to the μS reported from skiing on snow with grip-waxed cross-country skis. Also, a new type of roller ski with a camber and adjustable grip function was evaluated. The results showed that ratcheted wheel roller skis, on a treadmill rubber mat and on dry and wet asphalt surfaces, reached μS values that were five to eight times greater than the values reported from on-snow skiing with grip-waxed cross-country skis. For the roller skis with a camber and adjustable grip function, the μs could be varied from no grip at all up to the level of the tested ratcheted wheel roller skis.
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| 2. |
- Jensby Nedergaard, Niels, et al.
(författare)
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The effect of light reflections from the snow on kinematic data collected using stereo-photogrammetry with passive markers
- 2014
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Ingår i: Sports Engineering. - : Springer Science and Business Media LLC. - 1369-7072 .- 1460-2687. ; 17:2, s. 97-102
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Tidskriftsartikel (refereegranskat)abstract
- This study aimed to compare kinematic data collected during ski-cross starts outdoors on snow in daylight (high albedo) to similar data collected indoors with infiltrating sunlight but without light reflections from the snow (low albedo) using a video-based motion capture system with the active filtering function enabled. A 12-camera 3D motion capture system (Qualisys AB, Sweden) was used to measure test objects and eight skiers performing a ski-cross start on a slope outdoors and on a wooden start ramp indoors. The average residuals and standard deviations of the length of the calibration wand calculated indoors and outdoors by the calibration software were compared using descriptive statistics. Static and moving fixed length measures and thigh length measures were compared using Bland-Altman plots. Calibration residuals were slightly increased outdoors (1.77 mm) compared to indoors (1.54 mm), while wand length varied by 3.63 and 1.51 mm, respectively. Fixed static lengths differed by -8.65 ± 4.94 mm (shorter indoors), whereas fixed moving lengths differed by 0.85 ± 1.05 mm (longer indoors). A randomly chosen marker pair on one segment (Thigh) showed a mean difference of 1.19 ± 22.05 mm (longer indoors). It is concluded that 3D motion capture outdoors on snow in daylight is feasible, provides kinematic data comparable to indoors, and could be used to research biomechanics in snow sports.
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| 3. |
- Nilsson, Johnny, et al.
(författare)
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A new device for measuring ski running surface force and pressure profiles
- 2013
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Ingår i: Sports Engineering. - : Springer. - 1369-7072 .- 1460-2687. ; 16:1, s. 55-59
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Tidskriftsartikel (refereegranskat)abstract
- The pressure/force acting between the running surface of a ski and the snow may indirectly change glide friction. Thus, measuring the pressure/force distribution may be important for a deeper understanding of glide in skiing. The present aim was to construct a device that allowed the pressure/force underneath the ski running surface (SRS) to be recorded. Pressure sensors were attached on top of a platform. Sheets of different materials were used to improve the interaction between the SRS and the sensors. Possible functions of the device are demonstrated in three applications that emphasized comparison of force distribution underneath skis selected for similarity, force distribution under both skis and a single ski as well as backward weight distribution. The results show that the device with the pressure sensors mapped pressure/force distribution underneath the skis in the applications presented, and the system can thus be a useful tool for further optimizing e.g., ski designs.
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| 4. |
- Sundström, David, 1986-, et al.
(författare)
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Comparing bioenergetic models for the optimisation of pacing strategy in road cycling
- 2014
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Ingår i: Sports Engineering. - : Springer London. - 1369-7072 .- 1460-2687. ; 17:4, s. 207-215
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Tidskriftsartikel (refereegranskat)abstract
- Road cycling performance is dependent on race tactics and pacing strategy. To optimise the pacing strategy for any race performed with no drafting, a numerical model was introduced, one that solves equations of motion while minimising the finishing time by varying the power output along the course. The power output was constrained by two different hydraulic models: the simpler critical power model for intermittent exercise (CPIE) and the more sophisticated Margaria–Morton model (M–M). These were compared with a constant power strategy (CPS). The simulation of the three different models was carried out on a fictional 75 kg cyclist, riding a 2,000 m course. This resulted in finishing times of 162.4, 155.8 and 159.3 s and speed variances of 0.58, 0.26 and 0.29 % for the CPS, CPIE and M–M simulations, respectively. Furthermore, the average power output was 469.7, 469.7 and 469.1 W for the CPS, CPIE and M–M simulations, respectively. The M–M model takes more physiological phenomena into consideration compared to the CPIE model and, therefore, contributes to an optimised pacing strategy that is more realistic. Therefore, the M–M model might be more suitable for future studies on optimal pacing strategy, despite the relatively slower finishing time.
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| 5. |
- Swarén, Mikael, et al.
(författare)
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Testing method for objective evaluation of cross-country ski poles
- 2013
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Ingår i: Sports Engineering. - : Springer Science and Business Media LLC. - 1369-7072 .- 1460-2687. ; 16:4, s. 255-264
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the study was to develop an objective classification method for cross-country ski poles. A test device was designed to expose different pole models to maximal loading and impact tests. A load cell measured the axial forces in the pole shafts, and a laser distance meter measured shaft deflection when a load was applied via the wrist strap. In the loading tests, each shaft reached a plateau where no more force could be transferred. This maximal force transfer (MFT) value was a characteristic measure for flexural rigidity and thereby also strength. The developed test method enables a loading that is more similar to real-life skiing than a standard three-point bending test. Results show that the introduction of shaft indices for buckling strength is beneficial for comparison purposes. The MFT is a relevant parameter used in the characterization of poles.
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