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A new method to measure 3-D ground reaction forces during skiing on snow
Abstracts-InternationalSocietyof BiomechanicsXIV Congress1993
763
A NE” ME-‘;IODTO MEASURE3-D GROUNDREACTIONFORCESDURINGSKIINGON SNOW. Ant? Lepo&/uori’,MattiKarras”, HeikkiRusko* and JukkaT.Viitasalo’ ’ ResearcCInstitutefor OlympicSports,Jyv&kyU, * Departmentof Elect.Engineering,Universityof Oulu,Finland The purposeof this study was to developa new methodfor recordinga 3-D groundreactionforce distribution(GRFD) undervariouspartsof free style skis duringskiing on snow The 2.20 m long platform(20 horizontalbeams0.10 m wide and 1.50 m long)was placedin an 8” uphilland buriedur,dersnow to form part of a ski track.To locatethe ski on the platformand to visualisethe phasesof the kick, the performanceof a test skier was recordedsimultaneously to GRFD recordingsby two video cameras(80 Hz) and analysedby APAS.The systemwas testedusingskatingtechniques,on pwder sow (-2C”- -4C”). One pair of skis for we.+ sIIY.. nntAn2nd cne pair for pOVJde: snow were tested. Seam foice components(Fz, F, and Fy) and sums of momentarybeamforces(ZF,, ZFx and CFy) were averagedfor bothski pairs usingdata from eightseparatekicks per ski pair and testedstatisticallywith OnewayANOVAprocedure.Therewere no significantdifferencesin summedforce or impulseparametersbetweenthe ski pairs.To studythe dynamicpropertiesof the skis more closely,the beginningof the final kick phase,when the ski was edged strongly,was chosenfor further analysis.Significantdifferencesbetweenthe ski pairswere foundin this momentin ail directionsin beamforces.In the Fz the locationsof differenceswere underthe heel and 0.20 - 0.33 m to the tail of the ski boot. In the Fy and F, directions differenceswere found0.50 m to the tail from the heel,and underthe heelof the ski boot.Negativevalueswere foundin the F, and Fy directions.The locationsof the negativeforceswere 0.10- 0.20 m in frontof the peak positiveFz, 10 cm to the tail from the heel of the ski boot. The initialtest runs showedthat the new methodprovidedinformationon the 3-D groundreactionforcedistributionalongthe ski length. l
VALIDITY AND ACCURACY OF FOUR METHODS FOR LOCATING THE CENTER OF MASS OF YOUNG MALE AND FEMALE ATHLETES Paolo de Leva Kinesiology Department, Indiana University, Bloomington, IN 47405, USA A high precision reaction board, equipped with two load cells for measuring ground reaction forces, was utilized to determine the 20 horizontal coordinates of the CM of 9 female and 18 male young athletes, while assuming four body attitudes. At the same time, the subjects were photographed for locating their CM with the segmental method. The reaction board data served as a criterion to assess the accuracy of four variants of the segmentai method (geometrical models were not included, although very accurate, because of their impractical application). Two major sources of error in the CM mean position were identified: the use of cadaver data (e.=44mm in layout position), for their lack of validity when applied to the study of young athletes, and the assumption that the trunk CM Iii on the line joining its endpoints, invalid when the spine is flexed (a 20mm error in the body CM mean position was estimated to be induced by moderate forward spine flexion). Accuracy was dramatically improved (e.clOmm for all attitudes) when these sources of error were removed. The most accurate results were obtained with the method based on the mass and CM proportions repotted by Zatsiorsky et al. (1990), adjusted for using joint centers as segment endpoints. A mathematical model for estimating the CM of the fiexed trunk, based on the coordinates of only three landmarks (proximal, middle, distal), was successfully utilized for controlling the error due to spine flexion.
METHODS FOR ASSESSMENTS OF IMPACTS ON THE HAND-ARM SYSTEM FROM NUTRUNNERS. Lars Lindbeck, Steve Kihlberg and Anders Kjellberg. National Institute of Occupational Health S-171 84 SOLNA, Sweden. Impulsive reactions from hand held power tools have been associatedwith cumulative trauma disorders in the upper extremities. The purpose of this study was to investigate if ground force reactions and/or displacementsof the tool could be relevant quantities to assessthe effect from impacts on the hand-arm system.A simple method for measuringthe displacementby meansof a goniometer was also examined. Nine angle nut runners were studied with different pre-set torques, 25 Nm, 50 Nm, and 75 Nm, and three different types of shut-off mechanisms,viz. 1) a fast shut-off which was almost instantaneous,2) a slow shutoff with a declining torque-time curve, and 3) a delayed shut-off where the maximum torque was acting a while before shut-off occurred. Twelve subjectsperformed securingsof threadedfastenerswith the tools. Ground force reactions and motions were registeredduring the operationsby meansof a Kistler force plate, a SelspotII system and a Penny & Giles goniometer. The subjectsrated the strengthof the impact and the discomfort causedby the impacts using a modified Borg’s scales. The ratings were highly correlated to both the displacementsof the arm/tool and the measuredground reactions.The displacementof the wrist as measuredby the Selspot system was very closely correlated to the handledisplacementas measuredby the goniometer.There were also good correlations between the discomfort ratings and horizontal and vertical ground force reactions.The study suggeststhat both the ground force reactions and the displacementsof the tool handle during the operation might be relevant quantitaties to assessthe impact effect on the hand-arm system.The goniometer offers a good possibility to make simple measurementsof the displacementsin field studies.
763
A NE” ME-‘;IODTO MEASURE3-D GROUNDREACTIONFORCESDURINGSKIINGON SNOW. Ant? Lepo&/uori’,MattiKarras”, HeikkiRusko* and JukkaT.Viitasalo’ ’ ResearcCInstitutefor OlympicSports,Jyv&kyU, * Departmentof Elect.Engineering,Universityof Oulu,Finland The purposeof this study was to developa new methodfor recordinga 3-D groundreactionforce distribution(GRFD) undervariouspartsof free style skis duringskiing on snow The 2.20 m long platform(20 horizontalbeams0.10 m wide and 1.50 m long)was placedin an 8” uphilland buriedur,dersnow to form part of a ski track.To locatethe ski on the platformand to visualisethe phasesof the kick, the performanceof a test skier was recordedsimultaneously to GRFD recordingsby two video cameras(80 Hz) and analysedby APAS.The systemwas testedusingskatingtechniques,on pwder sow (-2C”- -4C”). One pair of skis for we.+ sIIY.. nntAn2nd cne pair for pOVJde: snow were tested. Seam foice components(Fz, F, and Fy) and sums of momentarybeamforces(ZF,, ZFx and CFy) were averagedfor bothski pairs usingdata from eightseparatekicks per ski pair and testedstatisticallywith OnewayANOVAprocedure.Therewere no significantdifferencesin summedforce or impulseparametersbetweenthe ski pairs.To studythe dynamicpropertiesof the skis more closely,the beginningof the final kick phase,when the ski was edged strongly,was chosenfor further analysis.Significantdifferencesbetweenthe ski pairswere foundin this momentin ail directionsin beamforces.In the Fz the locationsof differenceswere underthe heel and 0.20 - 0.33 m to the tail of the ski boot. In the Fy and F, directions differenceswere found0.50 m to the tail from the heel,and underthe heelof the ski boot.Negativevalueswere foundin the F, and Fy directions.The locationsof the negativeforceswere 0.10- 0.20 m in frontof the peak positiveFz, 10 cm to the tail from the heel of the ski boot. The initialtest runs showedthat the new methodprovidedinformationon the 3-D groundreactionforcedistributionalongthe ski length. l
VALIDITY AND ACCURACY OF FOUR METHODS FOR LOCATING THE CENTER OF MASS OF YOUNG MALE AND FEMALE ATHLETES Paolo de Leva Kinesiology Department, Indiana University, Bloomington, IN 47405, USA A high precision reaction board, equipped with two load cells for measuring ground reaction forces, was utilized to determine the 20 horizontal coordinates of the CM of 9 female and 18 male young athletes, while assuming four body attitudes. At the same time, the subjects were photographed for locating their CM with the segmental method. The reaction board data served as a criterion to assess the accuracy of four variants of the segmentai method (geometrical models were not included, although very accurate, because of their impractical application). Two major sources of error in the CM mean position were identified: the use of cadaver data (e.=44mm in layout position), for their lack of validity when applied to the study of young athletes, and the assumption that the trunk CM Iii on the line joining its endpoints, invalid when the spine is flexed (a 20mm error in the body CM mean position was estimated to be induced by moderate forward spine flexion). Accuracy was dramatically improved (e.clOmm for all attitudes) when these sources of error were removed. The most accurate results were obtained with the method based on the mass and CM proportions repotted by Zatsiorsky et al. (1990), adjusted for using joint centers as segment endpoints. A mathematical model for estimating the CM of the fiexed trunk, based on the coordinates of only three landmarks (proximal, middle, distal), was successfully utilized for controlling the error due to spine flexion.
METHODS FOR ASSESSMENTS OF IMPACTS ON THE HAND-ARM SYSTEM FROM NUTRUNNERS. Lars Lindbeck, Steve Kihlberg and Anders Kjellberg. National Institute of Occupational Health S-171 84 SOLNA, Sweden. Impulsive reactions from hand held power tools have been associatedwith cumulative trauma disorders in the upper extremities. The purpose of this study was to investigate if ground force reactions and/or displacementsof the tool could be relevant quantities to assessthe effect from impacts on the hand-arm system.A simple method for measuringthe displacementby meansof a goniometer was also examined. Nine angle nut runners were studied with different pre-set torques, 25 Nm, 50 Nm, and 75 Nm, and three different types of shut-off mechanisms,viz. 1) a fast shut-off which was almost instantaneous,2) a slow shutoff with a declining torque-time curve, and 3) a delayed shut-off where the maximum torque was acting a while before shut-off occurred. Twelve subjectsperformed securingsof threadedfastenerswith the tools. Ground force reactions and motions were registeredduring the operationsby meansof a Kistler force plate, a SelspotII system and a Penny & Giles goniometer. The subjectsrated the strengthof the impact and the discomfort causedby the impacts using a modified Borg’s scales. The ratings were highly correlated to both the displacementsof the arm/tool and the measuredground reactions.The displacementof the wrist as measuredby the Selspot system was very closely correlated to the handledisplacementas measuredby the goniometer.There were also good correlations between the discomfort ratings and horizontal and vertical ground force reactions.The study suggeststhat both the ground force reactions and the displacementsof the tool handle during the operation might be relevant quantitaties to assessthe impact effect on the hand-arm system.The goniometer offers a good possibility to make simple measurementsof the displacementsin field studies.