Browsing by Author "Karpul, David"

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    An investigation of potential kinematic factors associated with patellofemoral pain syndrome during running
    (2013) Allan, Christopher; Burgess, Theresa; Schwellnus, Martin; Karpul, David
    Patellofemoral pain syndrome (PFPS) is a common clinical condition affecting physically active individuals. It is characterised by pain behind or around the patella during loading of the lower limb. It is recognised that there are multiple factors that contribute to PFPS; however these factors are not well understood. There is equivocal evidence for differences in lower limb kinematics in participants with PFPS, particularly during the running gait cycle. The aim of this study was to investigate lower extremity kinematics during running in individuals with a history of PFPS compared to those without symptoms. Specific objectives: (a) To describe lower extremity kinematics during running for individuals with PFPS. (b) To determine whether there are differences in pelvis, hip, knee and ankle kinematics during running in participants with and without PFPS. (c) To determine whether there were any kinematic variables at the pelvis, hip and knee joint during stance phase of running that may be associated with an increased risk of developing PFPS. Methods: This study had a descriptive cross-sectional study design. Thirty one physically active individuals, who participated in at least two hours of physical activity per week for at least three months prior to testing, were recruited for the study. Fifteen participants presented with PFPS, and 16 participants without PFPS formed the control group. Participants were also required to have a Q-angle within the normal range for males (8.2º-14.2º) and females (11.4º-20.3º) respectively. Participants in the PFPS group were required to have a history of unilateral anterior or retro-patellar pain of non-traumatic origin that did not exceed a six-month period prior to testing. The participants’ PFPS also needed to be elicited during one or more symptom provocation tests, namely: resisted terminal knee extension, stair descent, or a unilateral partial squat. The PFPS participants had to be able to run without pain for a minimum period of 10 minutes, which allowed the running test to be completed without reproducing symptoms of PFPS. All participants gave written informed consent before taking part in the study. Participants were familiarised with all testing procedures. Participants completed medical and training questionnaires, and body composition measurements were performed. Sixteen retro-reflective markers were placed on anatomical landmarks of the lower limbs according to the modified Helen Hayes marker set. Participants were then required to perform a running test, which consisted of 10 sets of running at a self-selected speed on a 10 m pathway. Kinematic data of the pelvis, hip, knee and ankle were recorded by an eight-camera motion analysis system during each repetition of the test. The specific data extracted included range of motion at heel strike and toe off, peak range of motion during swing phase and stance phase. In addition, the range of motion travelled during stance and swing phases and the percentage of stance phase a participant took to reach the peak range of motion during stance phase were calculated.
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    Limiting factors in acoustic density separation of carbon particles in air
    (2009) Karpul, David; Tapson, Jonathan
    Particles suspended in a fluid that is exposed to an acoustic standing wave experience a time-averaged force that drives them to either the pressure nodes or anti-nodes of the wave. Several filter designs have been successfully implemented using this force to filter small particles in liquids with low flow rates and small cross-sectional areas. It has been suggested that the filtration of small solid particles out of a gas, such as carbon in air (smoke), would be a possible application of acoustic density separation. The emissions created by the combustion of hydrocarbons used in industrial processes, electricity production and transport significantly damage human health and the world at large. Particulate matter released, primarily by power plants, is currently removed from the emissions by highly space consuming and expensive equipment. The creation of a new type of particulate filter, which is both more cost effective and less space consuming, would be beneficial to the industry and consequently the environment at large. This study shows the limiting factors, in both power requirements and design factors, of an acoustic filter designed for filtering smoke particles across large cross-sectional areas at high flow rates, as in the case of an industrial smoke stack. It is shown that while filtration is possible, the power needed is impractical. It is also shown that operating the filter above a particular threshold intensity the energy usage of the filter is optimised.
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    On the application and generation of subsensory electrical nerve stimulation for the improvement of vibration perception in patients with HIV-related sensory neuropathy
    (2019) Karpul, David; Breen, Paul; Van Schaik, Andre; Heckmann, Jeanine
    This work investigates the application of Subsensory Electrical Noise Stimulation (SENS) to improve symptoms of HIV-related peripheral sensory neuropathy (HIVPN). HIV-PN occurs in roughly half of the 5 million people in South Africa with HIV. The disease has been shown to reduce quality of life and increase the risk of secondary ailments. Currently there is no treatment available. Previously, SENS has shown promise to improve tactile sensitivity in healthy populations and elderly individuals with peripheral neuropathic desensitisation. This work first establishes if SENS can improve the peripheral sensitivity of patients with HIV-PN, and secondly addresses practical aspects of using SENS in a therapeutic context. The vibrotactile sensitivity deficits of participants with HIV-PN and a matched control cohort is documented and analysed. It is found that HIV-PN participants have reduced sensitivity at all tested vibration frequencies (25 Hz, 50 Hz and 128 Hz), but especially at low frequencies. The interaction with vibration frequency indicates that HIV-PN may interact differently with different types of peripheral mechanoreceptors. SENS is then applied at four different amplitudes in an attempt to improve perception thresholds of the three vibration frequencies. SENS was shown to generally have a beneficial effect on 50 Hz vibration sensitivity for low SENS amplitudes. It had no effect, or a detrimental effect, at high SENS amplitudes, and also for 25 Hz and 128 Hz vibration frequencies. This work is also the first to document measures of pain with interventions of this type. No clear effects of SENS on sensations of pain were observed, which is a vital outcome if the therapy is to be developed further, since neuropathic pain is a frequent symptom of HIV-PN. The application of SENS as a practical therapy requires the accurate measurement of the participant’s electrical perception threshold, and a wearable device to apply the electrical signal on an ongoing basis. Research into the stability of electrical perception thresholds specifically aimed at subthreshold signals that would improve tactile sensitivity is presented. It was found that these thresholds vary wildly and correlated very little with possible explanatory variables, which introduces a new challenge for the development of SENS in future research. Currently there are no devices available to apply SENS in non-laboratory settings or for continuous use. The electronic design of a stimulator for using SENS as a wearable intervention is presented and characterised. The circuit is an efficient, low-power voltage to current converter that generates high voltages (120 V peak to peak) from a small, low-voltage rechargeable battery. The design and testing of control and instrumentation circuitry, as well as the addition of various safety and interface features is also documented. The battery life of the circuit is tested to operate for up to 33 hours and the circuit is tested to operate as expected in vivo. The results of this work demonstrate the potential viability of SENS as a therapy for HIV-PN, reveals the variability of electrical perception thresholds, explores the measures of pain for SENS interventions, and provides a complete and thoroughly tested design and implementation of an unparalleled electronic stimulator for nonlaboratory environments. The conclusions of this work form both a strong theoretical and practical basis for future SENS intervention research.
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    The relationship between the built environment and habitual levels of physical activity in South African older adults: a pilot study
    (BioMed Central Ltd, 2015) Kolbe-Alexander, Tracy; Pacheco, Kyla; Tomaz, Simone; Karpul, David; Lambert, Estelle
    BACKGROUND: Previous research has shown that the built environment plays a role in habitual levels of physical activity (PA), however much of this research has been conducted in adults and higher income countries. The aim of this pilot study was to examine the strength of association between the built environment and PA in South African older adults. METHODS: Participants were recruited (n=44, mean age 65+/-8.5years) from two suburbs, representing either a high socioeconomic (HSA) or low socioeconomic area (LSA). Self-reported PA, and subjective assessments of neighborhood walkability (Neighborhood Environment Walkability Scale, NEWS) was measured. Participants wore Actigraph GT3x accelerometers to objectively quantify PA. RESULTS: HSA participants reported significantly more leisure-time and less transport PA. Objectively measured and self-reported MVPA was significantly higher in HSA participants. NEWS 'Land-use Mix' was negatively associated with leisure-time MVPA, (r2=0.20; p<0.02). In addition, neighborhood aesthetics was positively associated with leisure-time physical activity (r2=0.33; p=0.02). 'Safety from traffic' was inversely associated with travel-related PA (r2=0.14, p=0.01). None of the other NEWS scores were associated with PA for the total group. CONCLUSION: Leisure-time and transport-related PA was influenced by socio-economic status. Attributes of the perceived built environment associated with leisure-time and total MVPA in older South Africa adults were different in low- and high- income settings.
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    Revealing complexities within flat-water kayaking: injury prevention and biomechanical analysis
    (2015) Fisher, Julia Marguerite; Tucker, Ross; Karpul, David; Noakes, Timothy
    Elite kayakers are required to perform repetitive movements that create strength and flexibility asymmetries in their bodies, making them susceptible to injury. The first portion of this thesis is dedicated to investigating whether a supervised, corrective pre-habilitation programme of the kinetic chain, conducted twice a week for 10 weeks, would reduce these predisposing factors. A group of 19 marathon paddlers were assessed before and after the intervention, with nine of them receiving the intervention. The 10-week intervention programme was found to significantly improve scapular position and kinesis, thoracic spine extension and single arm pulling ability, thus suggesting improved shoulder function and reduced risk of injury. The second portion of the thesis involved novel biomechanical analysis of kayaking on the water and on a kayaking-ergometer. It is the first objective description of the three dimensional movements of the kayak in the literature. Sprint and marathon paddlers performed a 180 metre time trial using an instrumented paddle with an accelerometer and gyroscope attached to the boat for analysis of boat movement characteristics and paddler-generated forces. Similar patterns for paddle torque, boat acceleration and pitch were observed between male sprint paddlers and male marathon paddlers. However, the direction and timing of the roll and the yaw of the boat during the water phase of the kayak stroke differed between these groups of paddlers. In addition, substantial individual variation existed within the group of male marathon paddlers. On the kayaking ergometer, activation patterns of the trunk and pelvic muscles were measured using electromyography during a maximal 200 metre time trial. Gluteus medius, lower trapezius and erector spinae were measured for the first time in maximal kayaking. The latissimus dorsi, pectoralis major and external oblique muscles were more active during the contralateral phase than has previously been reported. When these paddlers performed a single arm pull test on the same day, the muscle activation patterns changed, and muscle groups were active according to their anatomical function and what has previously been described. First, variation of movement, flexibility and segmental training of the kinetic chain may be advantageous when incorporated with kayaking training to prevent shoulder injury risk factors in paddlers. Second, individual evaluation of three-dimensional boat kinematics and muscle recruitment timing provides objective insight into an individual's kayak technique, with potential benefits for improving technical performance and mechanical efficiency.