Browsing by Author "Mathewson, Elizabeth"
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- ItemCoordination of place kicking in Rugby Union(Stellenbosch : Stellenbosch University, 2020-03) Mathewson, Elizabeth; Venter, Ranel; Cockcroft, John; Preatoni, Ezio; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Sport Science.ENGLISH ABSTRACT: Place kicking is a crucial skill in rugby as more than 40 per cent of the points scored in professional rugby matches are achieved by means of place kicks. Research in rugby kicking has mainly focussed on isolated segment position or movement, with limited literature on segments moving relative to each other. The aim of this study was to identify characteristics of place kicking technique from a coordination and coordination variability perspective. Ten male kickers performed five trials from three different distances (40 m, 32 m, and 22 m) in a range that proficient kickers should convert successfully 80 per cent of the time. An optoelectronic motion capture system consisting of ten cameras were used for capturing total body kinematic data. Data collection took place outdoor, on a rugby field. Data reductions included normalisation of kicking phases, extracting discrete kinematic variables, joint angles, joint and segment coordination patterns (hip-knee, knee-ankle, and pelvis-torso), and coordination variability measures. ANOVA comparisons were made on discrete data, while statistical parametric mapping repeated measures ANOVA analysis was used for continuous variables to determine differences groups differences. Coordination patterns were determined by means of vector coding technique. A bivariate method of calculating the area of the ellipse at each time point was used to determine the coordination variability. A hierarchal cluster analysis was performed on sagittal plane angles at kicking events to determine different technique profiles. Parameters such as greater hip extension and external rotation during the backswing (p=0.001, p=0.015) as well as increased pelvic external rotation (p=0.015) in the 40 m kicks compared to the 22 m and 32 m kicks are related to the formation of the tension arc in attempt to increase foot speed by means of the stretch-shortening cycle. The 40 m kicks had increase knee flexion (p<0.001), increasing the pre-stretch in the thigh muscles. Both factors allow greater force to be applied to kicking foot over greater distance during forward swing. During the forward swing a period of in-phase is reported as both the hip and the knee were flexing, creating a whip-like action. During the backswing the pelvis and thorax worked together to create a tension arc, while during the forward swing, the anti-phase with pelvis dominancy was seen. The pelvis was main mover for tension arc release, while the thorax stays more stable. Even though absolute changes in joint angles were seen, no changes were reported for the coordination patterns when kicking at different distances (22 m, 32 m, 40 m). An investigation into coordination variability found no differences between groups, indicating no change in movement strategy when kicking at different intensities. The cluster analysis revealed three clusters of sagittal plane kinematics describing a knee-dominant, hip-dominant as well as a combination technique. Stemming from the above, place kick training can benefit by coaching cues and drills focussing attention on tension arc formation, and the rhythm of movements. These results impart the knowledge that different distances require similar movement coordination strategies.
- ItemFoot posture in school children from the Western Cape: Differences between footwear use, gender and race(Stellenbosch : Stellenbosch University, 2016-12) Mathewson, Elizabeth; Venter, Ranel; Stellenbosch University. Faculty of Education. Dept. of Sport ScienceENGLISH ABSTRACT : The feet of children are sensitive to external forces as the ligaments, muscles and bones are still in the process of maturing. The arch develops naturally within the first ten years of life. This research study reports on the factors affecting foot posture and plantar pressure parameters by describing the differences between boys and girls, age groups, and race in South-Africa, as well as the differences between South-African and German children. A cross-sectional descriptive study where quantitative data were collected was used as the primary research method for this research study. Stratified randomised samples were selected consisting of 516 South-African children and 214 German children between the ages of six to eighteen years old. Testing equipment utilised include a manufactured foot calliper, as well as an EMED-SF® pressure plate. A barefoot scale was used to quantify the footwear habits of participants. A physical activity questionnaire developed specifically for older children (PAQ-C) and for adolescence (PAQ-A), were used to evaluate the physical activity level of the participants. Within the South-African sample, no significant differences were found in foot posture between boys and girls. Younger children had significantly lower arches in terms of the dynamic arch index (DAI) (younger than ten: 1.045 (0.030), older than ten: 1.041 (0.026)) (p = 0.025), as well as increased pliability values. Children younger than ten years old presented with greatest peak pressure under the medial heel, while children older than ten years old presented with greatest peak pressure under the big toe. When comparing the DAI of white South-African children (0.171 (0.069)) (p = 0.000) to that of mixed race South-African children (0.196 (0/067)), it is clear that the mixed race children have flattened arches compared to the white children. Mixed race children presented with more pliable feet (1.050 (0.030)) compared to white children (1.040 (0.026)) (p = 0.000), as well as a decreased contact area in all regions of the foot, except for the medial midfoot, as they have greater medial midfoot contact (p < 0.05). South African children had greater peak pressure in the medial forefoot and medial midfoot, as well as the big toe and toes two to five compared to German children (p < 0.05). Maximum force, was significantly greater for South-African children in all regions of the foot compared to German children except for the medial and lateral midfoot as well as the lateral forefoot (p < 0.05). The most significant differences were observed between children of different races. Mixed race children presented with lowered arches, more pliable feet and more dispersed peak pressures. With regards to the intercontinental results, South-African children load their feet more medially with increased gripping of the toes. The increased pressure-time integral in German children puts them at an increased risk of developing foot pain.