Browsing by Author "Lambert, Vicki"
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- ItemOpen AccessA comparison of indices of glucose metabolism in five black populations: data from modeling the epidemiologic transition study (METS)(2015-09-15) Atiase, Yacoba; Farni, Kathryn; Plange-Rhule, Jacob; Luke, Amy; Bovet, Pascal; Forrester, Terrence G; Lambert, Vicki; Levitt, Naomi S; Kliethermes, Stephanie; Cao, Guichan; Durazo-Arvizu, Ramon A; Cooper, Richard S; Dugas, Lara RBackground: Globally, Africans and African Americans experience a disproportionate burden of type 2 diabetes, compared to other race and ethnic groups. The aim of the study was to examine the association of plasma glucose with indices of glucose metabolism in young adults of African origin from 5 different countries. Methods: We identified participants from the Modeling the Epidemiologic Transition Study, an international study of weight change and cardiovascular disease (CVD) risk in five populations of African origin: USA (US), Jamaica, Ghana, South Africa, and Seychelles. For the current study, we included 667 participants (34.8 ± 6.3 years), with measures of plasma glucose, insulin, leptin, and adiponectin, as well as moderate and vigorous physical activity (MVPA, minutes/day [min/day]), daily sedentary time (min/day), anthropometrics, and body composition. Results: Among the 282 men, body mass index (BMI) ranged from 22.1 to 29.6 kg/m2 in men and from 25.8 to 34.8 kg/m2 in 385 women. MVPA ranged from 26.2 to 47.1 min/day in men, and from 14.3 to 27.3 min/day in women and correlated with adiposity (BMI, waist size, and % body fat) only among US males after controlling for age. Plasma glucose ranged from 4.6 ± 0.8 mmol/L in the South African men to 5.8 mmol/L US men, while the overall prevalence for diabetes was very low, except in the US men and women (6.7 and 12 %, respectively). Using multivariate linear regression, glucose was associated with BMI, age, sex, smoking hypertension, daily sedentary time but not daily MVPA. Conclusion: Obesity, metabolic risk, and other potential determinants vary significantly between populations at differing stages of the epidemiologic transition, requiring tailored public health policies to address local population characteristics.
- ItemOpen AccessApplication and development of indirect measures of free-living energy expenditure(2004) Keytel, Lara; Lambert, VickiThe aims of this thesis were to explore the accuracy in measuring free-living total daily energy expenditure (TDEE), by examining existing indirect measures of energy expenditure (EE) measurement and further, developing new techniques, for improved accuracy and application, in population-based studies. In a number of the studies, the research focus is the heart rate (HR) monitoring technique, for TDEE estimation as a result of its low cost and ease of implementation in large population-based studies. This thesis represents a progression from the application of the HR monitoring technique for estimating EE in response to training, or as a means to validate a physical activity recall instrument. However, what is highlighted are the limitations of the existing methodology for estimated TDEE in this way. Therefore, this thesis introduces a novel concept in the HR monitoring technique, incorporating group-based EE equations, and further, by including the effects of the previous minutes HR response on the estimation of EE from HR. Finally, this thesis validates these modifications, using a respiration chamber, purpose-built as a part of this dissertation. It should be noted, however, that in some instances, the thesis was constrained by opportunistic sampling, or the fact that in the case of Chapter 4, the study sample was part of a larger study designed for another purpose. Nevertheless, the outcomes of this research, in particular, the group-based HR-EE prediction equations, have important implications for large population-based epidemiological research concerning physical activity dose-response. Bibliography: p. 227-253.
- ItemOpen AccessAssociation between smoking and total energy expenditure in a multi-country study(2014-10-04) Gonseth, Semira; Dugas, Lara; Viswanathan, Barathi; Forrester, Terrence; Lambert, Vicki; Plange-Rhule, Jacob; Durazo-Arvizu, Ramon; Luke, Amy; Schoeller, Dale A; Bovet, PascalAbstract Background The association between smoking and total energy expenditure (TEE) is still controversial. We examined this association in a multi-country study where TEE was measured in a subset of participants by the doubly labeled water (DLW) method, the gold standard for this measurement. Methods This study includes 236 participants from five different African origin populations who underwent DLW measurements and had complete data on the main covariates of interest. Self-reported smoking status was categorized as either light (<7 cig/day) or high (≥7 cig/day). Lean body mass was assessed by deuterium dilution and physical activity (PA) by accelerometry. Results The prevalence of smoking was 55% in men and 16% in women with a median of 6.5 cigarettes/day. There was a trend toward lower BMI in smokers than non-smokers (not statistically significant). TEE was strongly correlated with fat-free mass (men: 0.70; women: 0.79) and with body weight (0.59 in both sexes). Using linear regression and adjusting for body weight, study site, age, PA, alcohol intake and occupation, TEE was larger in high smokers than in never smokers among men (difference of 298 kcal/day, p = 0.045) but not among women (162 kcal/day, p = 0.170). The association became slightly weaker in men (254 kcal/day, p = 0.058) and disappeared in women (−76 kcal/day, p = 0.380) when adjusting for fat-free mass instead of body weight. Conclusion There was an association between smoking and TEE among men. However, the lack of an association among women, which may be partly related to the small number of smoking women, also suggests a role of unaccounted confounding factors.
- ItemOpen AccessBone health and physical activity through the various life stages(2003) Micklesfield, Lisa; Lambert, VickiThe aims of this thesis were to investigate the interaction between physical activity and bone health through various life stages, in order to better understand the determinants of adult bone mass and consequently, osteoporosis. All the studies have been carried out on the various ethnic groups that make up the population of South Africa, with widely divergent economic and sociocultural experiences, and therefore provide us with insight into determinants of bone health within the South African context. In this dissertation, we will explore the relationship and interactions between physical activity, and other lifestyle, physiological and demographic factors, on BMD and bone QUS parameters in the South African population. What sets this thesis apart is that we consider groups that are largely unstudied, groups undergoing demographic and epidemiological transitions, and even groups for whom physical activity may no longer provide protection for bone health.
- ItemOpen AccessMeasurement of physical activity and associated health and functional outcomes in older South Africans(2004) Kolbe-Alexander, Tracy; Lambert, VickiThe aim of the first study was to measure validity and reliability of two PA questionnaires, the Yale Physical Activity Survey for older adults (YPAS) and the short version of the International Physical Activity Questionnaire (IPAQ), in a group of South African older adults.
- ItemOpen AccessMeasurement of physical activity for public health purposes : validity and reliability of the International Physical Activity Questionaire(IPAQ)(2002) Bohlmann, Isabelle Marie Therese; Lambert, VickiPhysical inactivity is a well-recognized risk factor for chronic diseases of lifestyle and has been associated with an increased incidence of morbidity and mortality. Current recommendations for the "dose" of physical activity that may be regarded as "protective" for these chronic diseases are 30 minutes or more of moderate-intensity physical activity on most, or preferably all, days of the week. However, when quantifying physical activity, it is not clear which factors influence the reporting of moderate and vigorous activity levels. Even in the literature, there is lack of agreement on the energy expenditure corresponding to so-called 'moderate' and 'vigorous' physical activity. Background (study 1): Self- reported physical activity levels are inversely related to chronic disease risk factors. The strength of this association depends, in part, on quantifying the intensity of activity that may be regarded as 'moderate or vigorous', which may be confounded by individual and cultural perceptions of relative exercise intensity, age, fitness, height, and habitual levels of activity. Aim (study 1): The purpose of this study was to i) examine the individual and group differences in self-selected walking pace corresponding to symptoms used to describe moderate and vigorous intensity and ii) to determine factors that may be associated with these differences. Methods (study 1): A convenience sample of 63 women and 39 men were recruited (N=102). Subjects were asked to walk for six minutes on an indoor track at a pace they regard as 'moderate', rest until heart rate returns to pre-exercise levels, then walk at a pace they consider 'vigorous'. Habitual levels of energy expenditure (EE), maximal oxygen consumption (VO₂max) and% fat were also determined. Results (study 1): Mean self-selected walking pace for moderate activity levels was 5.54 km-h⁻¹ (95% Confidence Interval (C.I.): 5.40; 5.69), and corresponded to 58% of age-predicted maximum heart rate (%HR.max) (95% C.I.: 56; 60). Mean self-selected vigorous pace was 7.03 km·h⁻¹ (95% C.I.: 6.85; 7.20), at 72 % HR.max (95% C.I.: 69; 74). The %HR.max for both moderate and vigorous intensity physical activity fell within the ACSM recommendations (55- 69%HR.max for moderate intensity activities, and 70 - 89 % HR.max for vigorous intensity activities). Multivariate analysis revealed that the factors predicting self-selected walking speed were gender, age, VO₂max, % fat and habitual vigorous EE. The only significant predictor of moderate pace was VO₂max. Education, occupation and habitual moderate EE were not associated with walking speed or intensity. Conclusion (study 1): These results show that subjects could accurately differentiate absolute and relative walking intensities and understood what was meant by the terms 'moderate' and 'vigorous'. However, absolute pace and relative intensity may vary according to differences in gender, fitness, age, height, body fat% and habitual levels of vigorous activity. These factors are important to consider when prescribing exercise using descriptors such as "moderate" and "vigorous". Background (study 2): None of the various methods used to measure habitual physical activity in the general population have proven entirely satisfactory in terms of reliability and accuracy. A major problem is that no "gold standard" exists for the validation of various questionnaires that can be used in large sample population studies. Ongoing efforts to improve the validity and reliability of the measurement of physical activity by self-report will enable cross-cultural and international comparisons to examine secular trends. Aim (study 2): The second part of this study assessed the validity and reliability of a recently developed International Physical Activity Questionnaire (IPAQ) which was interviewer-administered in both a short and long version, and queried activity performed in a "usual" week. Methods (study 2): Urbanized subjects (N = 82) were selected from a wide range of educational, activity level and socio-economic backgrounds. The long version IPAQ was designed to quantify the average weekly time and energy expenditure spent in occupation, transport-related activities, household chores, and leisure time activities. The short version IPAQ was designed to measure total weekly moderate, vigorous, walking and sitting related activity. Test-retest reliability was reported as the intra-class correlation between calculated time and energy expenditure (METmin·w ⁻¹) in different questionnaire items determined from three IPAQ administrations. Validity was assessed using biometrical and physiological parameters as criterion measures (Computer Science and Applications. Inc. activity monitor counts, body mass index, estimated VO₂max, % fat). Results (study 2): Test-rest reliability coefficients for the long IPAQ ranged from r = 0.38 tor= 0.75, with the highest correlation coefficients obtained in work related activities, and the lowest in household chores. Test-retest reliability in the short IPAQ ranged from r= 0.32 tor= 0.71, with the highest correlations obtained for sitting and the lowest for total moderate activity. Criterion validity for CSA counts and total physical activity in the long IPAQ was r = 0.50 (P < 0.001), for CSA counts and total vigorous activity r = 0.35 (P < 0.01), and for CSA counts and total job activity r = 0.51 (P < 0.001). Measurement of reliability and validity in this South African population compared favourably to physical activity questionnaires used in other population studies. Conclusion (study 2): The IPAQ provides a relatively valid and reliable estimate of physical activity in this population. In evaluating the relationship between physical activity and morbidity, it is important to consider the accuracy and reliability of the tool used to measure self-reported activity. Failure to show an association may represent a real phenomenon, or may simply reflect the inability of the physical activity questionnaire used to detect true physical activity levels.
- ItemOpen AccessMetabolic and hormonal responses to altered carbohydrate availability and its effect on fatigue development(2005) Claassen, Amanda; Lambert, Vicki; Bosch, AndrewThe main aims of the series of studies comprising this thesis were to investigate the effect of altered endogenous carbohydrate (CHO) availability, achieved primarily by pre-exercise dietary manipulation and antecedent exercise exposure, on interindividual variability in metabolic and hormonal responses to dynamic, steady-state exercise. Further, this thesis examined the impact of altered blood glucose availability on fatigue development during prolonged exercise. In this regard, it was hypothesized that endogenous CHO availability and the associated metabolic sequelae would impact on effort perception during exercise and fatigue development.
- ItemRestrictedMind the gap: brain-behaviour barriers to successful weight loss maintenance(2015) Hume, David John; Lambert, VickiThe primary objectives of this dissertation were to investigate the behavioural and neurophysiological factors related to overweight and obesity, as well as to weight loss maintenance versus weight relapse in a purposively sampled group of healthy South African women. The battery of investigations was designed to explore two central hypotheses: First, weight loss induces several behavioural compensations related to habitual eating behaviour and daily physical activity (PA) practices which facilitate the generation of a chronic positive energy balance, thereby increasing the risk of weight regain in reduced-overweight and reduced-obese women. Second, overweight and obese women as well as those at risk of undergoing relapse exhibit heightened indices of visual food cue-reactivity in various regions of the brain associated with obesogenic eating and reward-seeking tendencies. The novelty of this thesis lies in that we ascertained dietary, PA and psychobehavioural variables through both subjective accounts and objective measurement. Moreover, we employed electroencephalography to objectively evaluate high resolution temporal changes in visual food cue processing to test our second hypothesis. Overweight and obesity treatments focus, for the most part, on dietary- and/or exercise-centred interventions to facilitate weight loss. Our data suggest that certain interaction effects exist between the perception of environmental food cues and variables such as dietary restraint, habitual fat intake, body shape dissatisfaction and total body adiposity [Note: this thesis is embargoed until 30 November 2016]
- ItemOpen AccessSelf-reported measures versus objective measures of physical activity and sedentary behaviour : impacts of cardiovascular fitness and physical activity(2014) Tomaz, Simone Annabella; Kolbe-Alexander, Tracy; Lambert, VickiPhysical activity (PA) and sedentary behaviour (SB) can be quantified with both self-report and objective measures, using questionnaires and accelerometers, respectively. There is a paucity of research investigating the possible influence that cardiorespiratory fitness and PA might have on the accuracy of self-reported of PA and SB. This is especially important with the increasing evidence around the risks of SB, independent of PA. The aim of this research study is to describe the difference between self-reported measures of moderate PA, vigorous PA and SB against their objectively measured counterparts. The secondary aim is to identify factors influencing the error in self-report measures; including cardiorespiratory fitness and levels of PA.
- ItemOpen AccessSources of error and bias in the assessment of dietary intake : 24-hour recalls and food records(1997) Meltzer, Shelly Tracy; Lambert, Michael I; Lambert, Vicki; Huskisson, JoanThe first aim of this dissertation was to validate the 24-hour recall method of dietary assessment and to identify possible sources of error and bias in a cross-cultural sample of South African women. The second aim of this dissertation was to determine the source and extent of inter-researcher variability associated with the interpretation of food intake records. The first study was designed to consider whether reporting error is dependent on individual subject characteristics such as ethnicity, body mass, body fatness, age and education, or whether it is due to the dietary assessment tool (i.e., the 24-hour recall). In this study 118 women (25-55 years old) representing different ethnic and language groups (51 Xhosa-speaking, 31 Afrikaans-speaking, 36 English-speaking), different job types ( 25 unemployed, 25 general assistants, 52 medics and para-medics and 16 administrative personnel) and different levels of education (5 with 6-7 years of schooling, 35 with 8-10 years of formal schooling, 43 with 11-12 years of formal schooling and 35 with post high school diploma or degree) consumed a meal that was based on what they reported to habitually eat. All food and beverages consumed were covertly weighed and this was compared to a 24- hour dietary recall performed on the following day. Results of this study showed that the overall variance in reporting error was low. The error was, however, nutrient specific and was related to certain subject characteristics. Under-reporting was greater for subjects with a higher percentage body fat mass and a greater body mass index. Subjects with a lower level of education were more likely to under-report absolute carbohydrate (g) intake, whereas subjects with a higher level of education tended to under-report dietary fat. Subjects with a greater knowledge of food and nutrition were more likely to under-estimate protein intake and overestimate carbohydrate intake. 'Seasonality' (fluctuations in food purchases due to income) affected body mass, socio-economic status and dietary reporting error. Under-reporting of fat intake (g) was greatest in subjects that experienced the most fluctuations in income. In the second study of this dissertation, three post graduate students in dietetics independently assessed and analyzed ten, 3-day food records. The specific areas of variability that were studied related to (i) the selecting of food names/codes on the computer dietary analysis program, (ii) the keying of data from the written dietary records (clerical errors) to the data storage file and, (iii) the conversion of food consumption quantities to gram weights (judgment errors). There were no systematic differences in the variability amongst dietitians in interpreting and analyzing dietary data in this study. The mean coefficient of variation for added sugar was 14.8 ± 12.6 (g) and for fat 7.1± 5.2 (g). In one subject, the range of difference in fat (kJ) intake assessed by the dietitians was as high as 1313 kJ. Conclusions: 1) Adiposity is a universal predictor for under-reporting of dietary intake. 2) Inaccuracies in dietary reporting are nutrient specific and may be influenced by social desirability bias (through education or knowledge of food), language, familiarity with certain foods and 'seasonality' in food purchases. 3) These same factors influence the choices of food and beverages that subjects make in a 'test meal' that is used to validate dietary intake 4) The variations in interpretation of the quality and quantity of reported food intake by the measurer is a source of experimental error that cannot be ignored and which may account, at least partially, for the difference between true and reported intake.
- ItemOpen AccessThree-Dimensional Body Volume Measurement From Two-Dimensional Images: Towards A Smartphone Application(2020) Majola, Khwezi; Mutsvangwa, Tinashe; Douglas, Tania; Lambert, VickiObesity poses a public health threat worldwide and is associated with a higher mortality, increased likelihood of diabetes, and an increased risk of cancer. When treating obesity, regular monitoring of metrics such as body mass index (BMI) and waist circumference has been found to result in improved health outcomes for patients. Three-dimensional (3D) scanners provide a useful tool to provide body measurements based on 3D images in obesity management. However, such scanners are often inaccessible due to cost. A smartphone image-based method able to produce 3D images may provide a more accessible measuring tool. As a step towards developing such a smartphone application, this project developed a method for 3D reconstruction of body images from two-dimensional (2D) images, using a full body 3D Gaussian process morphable model (GPMM). Separate GPMMs were trained to learn the shape of female and male human bodies. Gaussian process regression of the three-dimensional (3D) GPMM models onto two-dimensional (2D) images is performed. Corresponding landmarks on the 3D shapes and in the 2D images are employed in reconstruction. Measurements of body volume, waist circumference and height are then performed to extract information that is useful in obesity management. Different model configurations (shape model with arms; modified shape model with arms; shape model without arms; marginalised shape model without arms; shape model with different landmarks) were used to ascertain the most promising approach for the reconstruction. Each reconstructed body was tested for accuracy using the surface-tosurface distance per vertex, modified Hausdorff distance, and assessment of the measurements. Tests were performed using data from the same dataset used to build the model and generalised data from a different dataset. In all test cases, the best performing approach used shape models without arms when considering surface distances. However, the surface-to-surface distances errors were larger than those seen in literature. For body measurements, the best performing models varied with different models performing best for different measurements. For the measurements, the errors were larger than the allowable errors and larger than those found in literature. Landmark positions were evaluated separately and found to be imprecise. There are a few sources that contribute towards the reconstruction errors. Possible sources of error include an inability to interpret pose and landmark position errors. The major recommendations for future work are to use a model that incorporates both shape and pose and to use automatic landmarking methods. Regarding a pathway to a smartphone app, camera parameter information should be considered to improve processing of the images and smartphone orientation information should be considered to correct for distortions due to a tilted phone.
- ItemOpen AccessVoluntary physical activity : measurement and relationship to selected health parameters in rural black South Africans resident in the Limpopo Province, South Africa.(2012) Cook, Ian; Lambert, VickiThe use of objective measures of physical activity in addition to, or in place of, subjective or self-report measures of physical activity, is being increasingly promoted in Physical Activity Epidemiology research. This thesis investigates methodological issues related to the use of objective measures of physical activity and presents pioneering objectively measured physical activity survey results from a rural South African setting. In this series of studies, we firstly explored the sources of variance in the objective measure of physical activity (uni-axial accelerometer) as a function of residence and also movement monitor placement. Secondly, we highlighted the importance of Non-Exercise Activity Thermogenesis (NEAT) in a rural African setting and the importance of considering the full spectrum of accelerometer counts when contrasting rural and urban populations. Thirdly, we demonstrated novel approaches to pedometry data from a rural African setting, such that volume-intensity effects could be inferred, and using estimated energy expenditure whether current physical activity guidelines are met. Finally, we indentified that the current recommendations for physical activity and health, applied in a rural African setting, may miss important and possible health-promoting physical activity.