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  • Author: David G. Kerwin x
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Marianne J.R. Gittoes and David G. Kerwin

A modification to an existing mathematical model is described, which permits the determination of subject-specific inertia parameters for wobbling and rigid masses of female body segments. The model comprises segment-specific soft tissue, bone, and lung components. A total of 59 geometric solids (40 soft tissue, 17 bone, 2 lung) were used to represent the body components. Ninety-five anthropometric measurements were collected from 7 female participants and were used to develop and evaluate the model. The success of the model is evaluated using predicted mass and mass distribution. The overall absolute accuracy in predicted whole body mass was better than 3.0%, with a maximum error of 4.9%. The appropriateness of the cadaver-based density values used in the model is addressed and the accuracy of the component inertia model in relation to uniform density models is discussed. The model offers a novel approach for determining component inertia parameters, which have been used successfully in a wobbling mass model to produce realistic kinetic analyses of drop-landings.

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Sharon J. Dixon and David G. Kerwin

This study investigated the influence of heel lift interventions on the loading of the Achilles tendon for heel-toe runners. It was hypothesized that the peak Achilles tendon force and peak rate of loading would be reduced by the increase in heel lift, and that the peak Achilles tendon force would occur significantly later in stance. Achilles tendon forces were determined by calculating sagittal-plane ankle joint moments using inverse-dynamics techniques and dividing these moments by Achilles tendon moment arm lengths. Methods for estimating Achilles tendon moment arm length using skin markers were justified via MRI data for one participant. Seven participants underwent running trials under three heel lift conditions: zero, 7.5-mm, and 15-mm heel lift. Average magnitude and occurrence time of peak Achilles tendon force and peak rate of loading were determined for each condition over the 7 participants. Despite group reductions in peak Achilles tendon force and peak rate of loading for the increased heel lift conditions, statistical analysis (ANOVA) revealed no significant differences for these variables, p > 0.05. Individual participant observations highlighted varied responses to heel lift; both increases and decreases in peak Achilles tendon force were observed. For the group data, the time of peak impact force occurred significantly later in the 15-mm heel lift condition than in the zero heel lift, p < 0.05. It is suggested that the success of increased heel lift in treating Achilles tendon injury may be due to a later occurrence of peak Achilles tendon force in response to this intervention, reducing Achilles tendon average rate of loading. In addition, the individuality of Achilles tendon peak force changes with heel lift intervention highlights the need for individual participant analysis.

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Mark A. Brewin and David G. Kerwin

Numerous planar analyses of sports activities have utilized scaling techniques to convert image coordinates into real-space locations. While in certain circumstances, such as competition, the camera must be elevated above the activity and its tilt accounted for, the influence of tilt on reconstruction accuracy using scaling is currently unreported. A modification of the direct linear transformation (2D-DLT) which considers only the vertical plane provides an alternative approach for planar reconstruction. This study compared the reconstruction accuracy between scaling and 2D-DLT over a range of tilt angles throughout a 6-m horizontal field of view. Four calibration and 30 reconstruction markers of known locations in a vertical plane were videotaped from nine positions to provide tilt angles varying between –2° and +6°. Both techniques were used to estimate real-space locations for the reconstruction markers, and accuracy was calculated by comparing known and reconstructed locations. The smallest reconstruction errors were obtained using 2D-DLT and were unaffected by camera tilt. The scaling technique produced significantly larger (p < 0.01) errors than 2D-DLT, with the exception of 0° and +1° of tilt, and there was a detrimental effect on accuracy as the magnitude of tilt increased. The largest variations in reconstruction errors were associated with scaling, with markers at the extremes of the image showing the largest errors. The 2D-DLT approach provided accurate reconstruction data for planar analyses across the field of view and throughout the range of tilt angles, and should be preferred over scaling techniques.

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Maurice R. Yeadon and David G. Kerwin

At the 1996 Atlanta Olympic Games, 18 single somersaults with one twist in the women’s compulsory floor exercises were recorded using two video cameras. An 11 segment computer simulation model was used to analyze the twisting techniques used. It was found mat counter-rotation techniques accounted for less than one third of the twist for all gymnasts, indicating that the production of twist was mainly a consequence of the angular momentum and a non-zero tilt angle. Contributions to the tilt angle reached at the mid-twist position were used as measures of the twisting potential of various techniques. Contact techniques accounted for 30% of the tilt produced, the remainder being produced using aerial techniques, which primarily comprised a symmetrical lowering of the arms together with minor contributions from asymmetrical arm and hip movements. There was no evidence of a difference in technique between the highest and lowest scoring competitors.

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Sharon J. Dixon and David G. Kerwin

In this study sagittal plane joint angles of the lower extremity were used to obtain an indication of the influence of heel lift manipulation on Achilles tendon strain in running. The influence of increased heel lift on lower extremity kinematics was investigated for 8 heel striking subjects. With increased heel lift, all subjects demonstrated reductions in peak ankle dorsi-flexion and consistent values of peak knee flexion, indicating that there were reductions in peak Achilles tendon strain. Group analysis demonstrated that the reductions in peak ankle angle were statistically significant (p < .01). Typically, subjects also demonstrated adjustments in initial ankle angle, whereby the amount of ankle dorsi-flexion at initial ground contact was reduced with increased heel lift. Group mean data indicated that a 15-mm heel lift resulted in a mean decrease in initial ankle dorsi-flexion of 3.9°, while peak ankle dorsi-flexion was also reduced by 3.9°. It is suggested that the initial ankle angle adjustment acted to maintain a similar range of ankle joint movement in the period from initial ground contact to peak ankle dorsi-flexion across heel lift conditions. The distinct behavior of one subject, who demonstrated an increased ankle dorsi-flexion at ground impact, has highlighted the importance of considering single subject results in studies of footwear variation in running.

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Sharon J. Dixon and David G. Kerwin

In this study, a modeling method was developed to estimate Achilles tendon forces in running. Owing to the common use of heel lift devices in the treatment of Achilles tendon injury, we investigated the influence of increased heel lift on Achilles tendon loading. The hypothesis was that heel lift manipulation can influence maximum Achilles tendon force. Responses to heel lift variation were found to differ among 3 elite runners demonstrating distinct running styles. A rearfoot and a midfoot striker demonstrated significant increases in maximum Achilles tendon force with increased heel lift, whereas a forefoot striker demonstrated no changes in maximum Achilles tendon force values with heel lift manipulation (p < .05). Analysis of the factors contributing to the observed changes in maximum Achilles tendon force highlighted the influence of the moment arm of ground reaction force and the moment arm of the Achilles tendon about the ankle joint center. The finding that increased heel lift may increase maximum Achilles tendon force suggests that caution is advised in the routine use of this intervention. The different responses to heel lift increase between subjects highlight the importance of classifying subjects based on running style.

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Marianne J. R. Gittoes and David G. Kerwin

This study aimed to gain insight into the individual and interactive effects of segmental mass proportions and coupling properties on external loading in simulated forefoot landings. An evaluated four-segment wobbling mass model replicated forefoot drop landings (height: 0.46 m) performed by two subjects. A comparison of the peak impact forces (GFzmax) produced during the evaluated landing and further simulated landings performed using modified (±5% perturbation) mass proportions and coupling properties was made. Independent segmental mass proportion changes, particularly in the upper body, produced a prominent change in GFzmax of up to 0.32 bodyweight (BW) whereas independent mass coupling stiffness and damping alterations had less effect on GFzmax (change in GFzmax of up to 0.18 BW). When combining rigid mass proportion reductions with damping modifications, an additional GFzmax attenuation of up to 0.13 BW was produced. An individual may be predisposed to high loading and traumatic and overuse injury during forefoot landings owing to their inherent inertia profile. Subject-specific neuromuscular modifications to mass coupling properties may not be beneficial in overriding the increased forces associated with larger rigid mass proportions.

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David G. Kerwin, Maurice R. Yeadon and Sung-Cheol Lee

An 11-segment three-dimensional simulation model was used to modify the body configurations of eight gymnasts performing multiple somersault dismounts during the Men’s High Bar competition in the 1988 Seoul Olympic Games. Four layout double somersault performances were modified to change a characteristic backward arch to a straight body position. This modification reduced the somersault rotation by 0.03 to 0.10 somersaults. Four tucked triple somersault performances were modified so that the thigh abduction angle was reduced to zero. This modification resulted in underrotations ranging from 0.01 to 0.34 somersaults depending on the amount of thigh abduction in the original movement. The additional angular momentum needed for successful completion of the modified movements was small in general and in no case greater than 13%.

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Maurice R. Yeadon, Sung-Cheol Lee and David G. Kerwin

At the 1988 Seoul Olympic Games, eight full twisting somersault dismounts from the high bar were filmed using two cameras during the compulsory exercises of the Men’s High Bar competition. Angles describing body configuration and orientation were determined and were input into a computer simulation model of aerial movement. The deviations between simulation and film were less than 2.5° for tilt angles and less than 0.07 revolutions for twist angles. The twisting techniques employed were quantified using the tilt angle as a measure of twisting potential. Contributions to the maximum tilt angle were determined using simulations based on modifications of the film data. Each of the eight competitors obtained most of the tilt using aerial rather than contact techniques. In general, the majority of the aerial contributions arose from asymmetrical arm and hip movements.

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David G. Kerwin, Maurice R. Yeadon and Michael J. Harwood

The release from the high bar was analyzed for six performances of triple backward somersaults. All 6 gymnasts released the bar with their mass centers below the level of the bar. The mean horizontal velocity of the mass center away from the bar was 1.2 m · s−1. This horizontal velocity was partitioned into contributions from the tangential and radial motions of the mass center relative to the bar and the movement of the bar relative to its neutral position. It was found that the tangential motion was the major contributor although the radial motion produced substantial positive contributions and the bar movement gave large negative contributions in two cases.