Doctoral Degrees (Exercise, Sport and Lifestyle Medicine)

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Browsing Doctoral Degrees (Exercise, Sport and Lifestyle Medicine) by browse.metadata.advisor "Cockcroft, John"

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    Coordination 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.
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    Effects of a barefoot intervention programme on the landing kinetics and kinematics of netball players
    (2018-12) Jaiyesimi, Boluwaji Gbenga; Venter, Ranel; Cockcroft, John; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Sport Science.
    ENGLISH ABSTRACT: Effective landings, as a component of movement tasks in many sports, have a significant role during ground contact and subsequent kinetic chain intersegmental interactions. Landings are frequently performed tasks in sports to manipulate skills, maximise mechanical functions of the body and to possibly avoid injury. The rationale of biomechanical studies on landing in netball focuses on the reduction of risk of lower extremity injuries and enhance performance. The trauma of injury to a female athlete ranges from immobility, disengagement from the team to psychophysiological stress and physical deterioration. The primary aim of the study was to determine the acute differences in landing kinetics and kinematics between barefoot and shod conditions in netball players. The secondary aim was to determine effect of a six-week barefoot training intervention on landing biomechanics in netball players. The experimental design adopted for the study was a pretest-posttest randomized groups design. Thirty netball players were recruited for the study and randomly allocated into an experimental (EXP) (n = 15) or a control group (CON) (n = 15). The players performed jump-landing tasks (single-leg drop landing right and left) (SLR and SLL), a drop vertical jump (DVJ) and a stop-jump performance task (SJPT) in barefoot (BF), and shod (SH) conditions. The intervention for the study spanned a 6-week period with 18 training sessions over this period. Ground reaction forces, time to peak ground reaction forces and shock attenuation were considered for kinetic variables while impact peak acceleration, initial contact angles, peak angles and range of motion were considered for kinematic variables. A 3D force plate (sampled at 1000 Hz) was used to capture force data while a wireless inertial motion capture system (sampled at 200 Hz, filtered with Butterworth 60 Hz low-pass), was used to capture kinematic data. The Subjective evaluation of the Landing Error Scoring System (LESS), Modified Lower Limb Comfort Index (mLLCI) and barefoot activity experience was adopted for qualitative assessment of the study. Mean, standard deviation, standard error of mean, and percentage differences were used in the descriptive analysis while Chi-square, independent t-tests and a mixed model ANOVA were used in the inferential analysis. The results showed a non-significant reduction in peak resultant force and vertical ground reaction forces for the jump-landing tasks in SH condition. The mediolateral ground reaction force was significantly lower in BF condition for some of the jump-landing tasks (SLL p = 0.02; DVJ p = 0.03). It was further shown that sagittal plane kinematics increased at initial contact in BF condition but decreased at peak angle. The frontal plane kinematics increased in BF more than SH conditions at initial contact but decreased at peak angle. The EXP (p = 0.00) and CON groups (p = 0.00) had significant changes in knee shock attenuation after the intervention. However, the CON group had more shock attenuation at the knee and ankle during the jump-landing tasks. The feedback of subjective experience of barefoot activities after the intervention showed that the negative experience of injury risks and significant others did not outweigh the positive perception of neuromuscular benefits and other related factors. In conclusion, BF training could form part of training modalities implemented to enhance safe and effective landings. Coaches need to be educated on the implementation of an injury prevention programme, including emphasis on effective landings, to possibly reduce the incidence of lower limb injuries in netball. Keywords: Barefoot, kinetics, kinematics, shock attenuation, impact peak acceleration