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Objective Analysis Methods in the Mechanics of Sports
KTH, School of Engineering Sciences (SCI), Mechanics.ORCID iD: 0000-0001-5234-6554
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Sports engineering can be considered as the bridge between the knowledge of sports science and the principles of engineering and has an important role not only in improving the athletic performance, but also in increasing the safety of the athletes. Testing and optimization of sports equipment and athletic performance are essential for supporting athletes in their quest to reach the podium. However, most of the equipment used by world-class athletes is chosen based only on subjective tests and the athletes’ feelings. Consequently, one of the aims of this thesis was to combine mechanics and mathematics to develop new objective test methods for sports equipment. Another objective was to investigate the possibility to accurately track and analyse cross-country skiing performance by using a real-time locating system. A long term aim is the contribution to increased knowledge about objective test and analysis methods in sports. The main methodological advancements are the modification of established test methods for sports equipment and the implementation of spline-interpolated measured positioning data to evaluate cross-country skiing performance. The first two papers show that it is possible to design objective yet sport specific test methods for different sports equipment. New test devices and methodologies are proposed for alpine ski helmets and cross-country ski poles. The third paper gives suggestions for improved test setups and theoretical simulations are introduced for glide tests of skis. It is shown, it the fourth paper, that data from a real-time locating system in combination with a spline model offers considerable potential for performance analysis in cross-country sprint skiing. In the last paper, for the first time, propulsive power during a cross-country sprint skiing race is estimated by applying a power balance model to spline-interpolated measured positioning data, enabling in-depth analyses of power output and pacing strategies in cross-country skiing. Even though it has not been a first priority aim in this work, the results from the first two papers have been used by manufacturers to design new helmets with increased safety properties and cross-country ski poles with increased force transfer properties. In summary, the results of this thesis demonstrate the feasibility of using mechanics and mathematics to increase the objectiveness and relevance when analysing sports equipment and athletic performance.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , 32 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2016-13
Keyword [en]
sports equipment, test methods, sports mechanics, biomechanics, performance analysis, tracking, positioning system, pacing, alpine skiing, cross-country skiing, poles, helmets
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-193044ISBN: 978-91-7729-094-0 (print)OAI: oai:DiVA.org:kth-193044DiVA: diva2:974604
Public defence
2016-10-20, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160927

Available from: 2016-09-27 Created: 2016-09-27 Last updated: 2016-09-27Bibliographically approved
List of papers
1. Repeated low impacts in alpine ski helmets
Open this publication in new window or tab >>Repeated low impacts in alpine ski helmets
2013 (English)In: Sports Technology, ISSN 1934-6190, Vol. 6, no 1, 43-52 p.Article in journal (Refereed) Published
Abstract [en]

Alpine ski race helmets are subjected to multiple impacts during a race caused by the skiers hitting the gates on their way down the course. This study investigated the difference between expanded polystyrene (EPS) and expanded polypropylene (EPP) cores in alpine ski race helmets when subjected to repetitive violence, caused by alpine slalom gates. A special test rig was developed where a rotating slalom pole impacted the helmets with a velocity of 13.3 m·s- 1. All helmets (six EPS and six EPP) were attached to a headform, monitored with a triaxial accelerometer at the center of mass. Each helmet sustained 1000 impacts and acceleration data were collected around every 200 impacts. No significant differences were observed between the first hit and after 1000 hits for either the EPS or the EPP helmets. However, the total group mean acceleration and mean peak acceleration were 15% and 16% higher, respectively, for the EPS series compared with the EPP series. Also, all EPS helmets showed cracked cores after 1000 impacts compared with 1 cracked EPP core. Findings suggest that EPP cores might be more suitable for absorbing multiple low impacts caused by alpine gates and that repeated violence is a relevant parameter to consider when constructing alpine ski race helmets.

Keyword
head acceleration, alpine skiing, multiple impacts
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-103298 (URN)10.1080/19346182.2012.744413 (DOI)2-s2.0-84893933854 (Scopus ID)
Note

QC 20130515

Available from: 2012-10-10 Created: 2012-10-10 Last updated: 2016-09-27Bibliographically approved
2. Testing method for objective evaluation of cross-country ski poles
Open this publication in new window or tab >>Testing method for objective evaluation of cross-country ski poles
2013 (English)In: Sports Engineering, ISSN 1369-7072, E-ISSN 1460-2687, Vol. 16, no 4, 255-264 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Bending, Buckling, Force transfer, Impact
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-139892 (URN)10.1007/s12283-013-0139-6 (DOI)2-s2.0-84888024383 (Scopus ID)
Note

QC 20140116

Available from: 2014-01-16 Created: 2014-01-15 Last updated: 2017-12-06Bibliographically approved
3. Validation of test setup to evaluate glide performance in skis
Open this publication in new window or tab >>Validation of test setup to evaluate glide performance in skis
2014 (English)In: Sports Technology, ISSN 1934-6182, E-ISSN 1934-6190, Vol. 7, no 1-2, 89-97 p.Article in journal (Refereed) Published
Abstract [en]

Although today's ski waxing chemicals and micro-machining techniques of the ski base are highly sophisticated, objective procedures for testing and verification of the results have not yet been developed and evaluation is based on comparison of subjective experience. The purpose of the present study was thus to compare different setups for testing the glide of cross-country skis. Two differently waxed ski pairs were tested for glide inside a ski tunnel. Inertial measurement units (IMUs) were attached to each ski; instantaneous velocities monitored by three different speed-traps; the velocities during the acceleration phase determined by Doppler radar. Kinetic, potential and total energy, giving the energy dissipation, were calculated for four representative trials during the acceleration phase. No reliable data were obtained from the IMUs due to high drift. The mean maximal velocity for the two ski pairs were 6.97, s = 0.09 and 6.70, s = 0.09 m·s − 1, respectively. Higher differences between the skis were identified during the retardation phase compared to the acceleration phase. The mean difference between the velocities determined by the speed-trap and Doppler radar was 0.6, s = 1%, demonstrating that the latter provides accurate data for evaluation of gliding characteristics and performance. However, theoretical confirmation of the friction coefficient, on the basis of data provided by Doppler radar and energy calculations requires exact measurements of the inclination and topography of the track in question.

Place, publisher, year, edition, pages
Routledge, 2014
Keyword
alpine, cross-country, friction, skiing, snow, wax
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-176220 (URN)10.1080/19346182.2014.968164 (DOI)2-s2.0-84938955462 (Scopus ID)
Note

QC 20151116 QC 20160923

Available from: 2015-11-16 Created: 2015-11-02 Last updated: 2017-12-01Bibliographically approved
4. Usage and validation of a tracking system to monitor position and velocity during cross-country skiing
Open this publication in new window or tab >>Usage and validation of a tracking system to monitor position and velocity during cross-country skiing
2016 (English)In: International Journal of Performance Analysis in Sport, ISSN 1474-8185, E-ISSN 1474-8185, Vol. 16, no 2, 769-785 p.Article in journal (Refereed) Published
Abstract [en]

For the first time, we investigate here the possibility of using a real-time locating system (RTLS) to track cross-country skiers during a competition. For validation, three RTLS tags were attached to the antenna of a real-time kinematics global navigation satellite system (RTK GNSS) carried by a skier, skiing the course at three different intensities. In addition, RTLS data were collected from 70 racers during a FIS cross-country skiing sprint race. Spline interpolations were fitted to the RTLS data. In comparison to the RTK GNSS, the spline models for the three RTLS tags overestimated the mean skiing velocity by 5% and 2% at low and medium intensities, respectively, with no difference between the two systems during high intensity. The corresponding overestimations of the peak velocity at skiing intensities were 15%, 10% and 8%, respectively. A decimated sampling frequency for the RTLS data from 50 Hz to 0.5 Hz resulted in lower typical mean errors for the x- (0.53 m vs. 1.40 m), y- (0.31 m vs. 1.36 m) and z-axis (0.10 m vs. 0.20 m). The spline models based on 0.5 Hz and 1 Hz RTLS data overestimated the finishing times by on average of 0.5 s and 0.3 s, respectively. If a sufficient number of locators is utilized and the number of tags simultaneously recorded is limited, this RTLS can track cross-country skiers accurately. In conclusion, a low RTLS sampling frequency in combination with a spline model offer considerable potential for analyzing performance during cross-country sprint skiing.

Place, publisher, year, edition, pages
Cardiff Metropolitan University, 2016
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-192849 (URN)000384915200027 ()
Note

QC 20160923

Available from: 2016-09-21 Created: 2016-09-21 Last updated: 2017-11-21Bibliographically approved
5. Power and pacing calculations based on real-time locating data from a cross-country skiing sprint race
Open this publication in new window or tab >>Power and pacing calculations based on real-time locating data from a cross-country skiing sprint race
(English)Manuscript (preprint) (Other academic)
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-192851 (URN)
Note

QC 20160923

Available from: 2016-09-21 Created: 2016-09-21 Last updated: 2016-09-27Bibliographically approved

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