Browsing by Author "Kroff, Jacolene"

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    An analysis of the partial feasibility of a novel cardiac exercise rehabilitation programme for patients suffering from cardiovascular disease
    (2022) Ross, Tayla Jane; Kroff, Jacolene; Atterbury, E
    Introduction: Substantial research has shown that the inclusion of exercise in cardiac rehabilitation has a favourable effect on many outcome variables, and that exercise should be considered a vital and central component for cardiovascular disease (CVD) rehabilitation. South Africans are facing a growing epidemic of CVD, which has major implications for healthcare services and has placed increasing strain on the already grabbling South African healthcare system. Cost-effective primary and secondary prevention and management strategies are needed to slow down the growing CVD epidemic and relieve strain on health-care systems. The need exists for more evidence to demonstrate that cardiac exercise rehabilitation programmes (CRPs) can significantly reduce readmissions, mortality, comorbidities, and improve quality of life. Aims: The aims of this study were to determine the partial feasibility of a novel CRP in a South African public hospital setting by evaluating the following: 1) The recruitment potential and sample population characteristics of those considered eligible to partake in the exercise component of a novel CRP; and 2) The testretest reliability of the tools utilized for the safe monitoring of the exercise intensity during the prospective CRP. Methods: The recruitment potential and sample population characteristics of the target population were determined via retrospective analysis of a hospital admission patient database spreading over three months. The database was searched for demographic data including age, sex, height, weight, waist circumference and BMI, the admission diagnosis, patient co-morbidities and medications. The test-retest reliability of the monitoring tools was conducted on apparently healthy participants who underwent a series of monitoring measures before and after a 6-min motion test on two separate occasions. The test-retest reliability of each monitoring tool was determined using intraclass correlation coefficients (ICCs), effect size calculation and Bland-Altman plots. Results: One hundred and nine patients (52.2%) were considered ineligible for a CRP, whereas 100 individuals (47.8%) were considered eligible. Significant differences were identified between the eligible and ineligible populations were for four comorbidities and two medications. Twenty-two outcome measures were assessed for reliability, five of which were classified as having “poor” reliability, nine as “moderate”, three as “good” and five as “excellent' according to ICCs. Eighteen measures revealed excellent test-retest reliability, and the remaining 8 measures (Baseline Systolic Blood Pressure; Baseline Diastolic Blood Pressure; Baseline Oxygen Saturation; Immediately Post-Exercise Oxygen Saturation; Immediately Post-Exercise RPE; 5-Minutes Post-Exercise Systolic Blood Pressure; 5-Minutes Post-Exercise Oxygen Saturation; and 5-Minutes Post-Exercise RPE) had showed small effect sizes between 0.2-0.5, which was considered acceptable. Conclusion: The results from the analysis of the recruitment potential from a public hospital setting reveal that approximately 33 patients (100 patients/3 months) will be eligible per CRP intake, and the recruitment potential of eligible patients currently exceeds the prospective resource and staff capacity of the CRP. Further investigation is required to address and resolve the shortcoming in resources to offer the CRP to all eligible participants. The results from the test-retest reliability of the monitoring tools used within the CRP revealed that most of the equipment and measures achieved sound reliability, except for the blood pressure monitors, pulse oximeters and RPE scale. Alternative devices for monitoring blood pressure, oxygen saturation and RPE are recommended.
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    Comparisons of intensity-duration patterns of physical activity in the US, Jamaica and 3 African countries
    (BioMed Central, 2014-08-27) Dugas, Lara R; Bovet, Pascal; Forrester, Terrence E; Lambert, Estelle V; Plange-Rhule, Jacob; Durazo-Arvizu, Ramon A; Shoham, David; Kroff, Jacolene; Cao, Guichan; Cooper, Richard S; Brage, Soren; Ekelund, Ulf; Luke, Amy
    Background: This difference in how populations living in low-, middle or upper-income countries accumulate daily PA, i.e. patterns and intensity, is an important part in addressing the global PA movement. We sought to characterize objective PA in 2,500 participants spanning the epidemiologic transition. The Modeling the Epidemiologic Transition Study (METS) is a longitudinal study, in 5 countries. METS seeks to define the association between physical activity (PA), obesity and CVD risk in populations of African origin: Ghana (GH), South Africa (SA), Seychelles (SEY), Jamaica (JA) and the US (suburban Chicago). Methods: Baseline measurements of objective PA, SES, anthropometrics and body composition, were completed on 2,500 men and women, aged 25–45 years. Moderate and vigorous PA (MVPA, min/d) on week and weekend days was explored ecologically, by adiposity status and manual labor. Results: Among the men, obesity prevalence reflected the level of economic transition and was lowest in GH (1.7%) and SA (4.8%) and highest in the US (41%). SA (55%) and US (65%) women had the highest levels of obesity, compared to only 16% in GH. More men and women in developing countries engaged in manual labor and this was reflected by an almost doubling of measured MPVA among the men in GH (45 min/d) and SA (47 min/d) compared to only 28 min/d in the US. Women in GH (25 min/d), SA (21 min/d), JA (20 min/d) and SEY (20 min/d) accumulated significantly more MPVA than women in the US (14 min/d), yet this difference was not reflected by differences in BMI between SA, JA, SEY and US. Moderate PA constituted the bulk of the PA, with no study populations except SA men accumulating > 5 min/d of vigorous PA. Among the women, no sites accumulated >2 min/d of vigorous PA. Overweight/obese men were 22% less likely to engage in manual occupations. Conclusion: While there is some association for PA with obesity, this relationship is inconsistent across the epidemiologic transition and suggests that PA policy recommendations should be tailored for each environment.
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    Fasting substrate oxidation in relation to habitual dietary fat intake and insulin resistance in non-diabetic women: a case for metabolic flexibility?
    (BioMed Central Ltd, 2013) Carstens, Madelaine; Goedecke, Julia; Dugas, Lara; Evans, Juliet; Kroff, Jacolene; Levitt, Naomi; Lambert, Estelle
    BACKGROUND: Metabolic flexibility described as "the capacity of the body to match fuel oxidation to fuel availability" has been implicated in insulin resistance. We examined fasting substrate oxidation in relation to dietary macronutrient intake, and markers of insulin resistance in otherwise healthy women, with and without a family history of diabetes mellitus (FH DM). METHODS: We measured body composition (dual x-ray absorptiometry), visceral and subcutaneous adipose tissue area (VAT, SAT, using Computerised Tomography), fasting [glucose], [insulin], [free fatty acids], [blood lipids], insulin resistance (HOMA-IR), resting energy expenditure (REE), respiratory exchange ratio(RER) and self-reported physical activity in a convenience sample of 180 women (18-45 yrs). A food frequency questionnaire was used to assess energy intake (EI) and calculate the RER: Food Quotient (FQ) ratio. Only those with EI:REE (1.05 -2.28) were included (N=140). Insulin resistance was defined HOMA-IR (>1.95). RESULTS: The Insulin Resistant (IR) group had higher energy, carbohydrate and protein intakes (p<0.05) and lower PA levels than Insulin Sensitive (IS) group (P<0.001), but there were no differences in RER or RER:FQ between groups. However, nearly 50% of the variance in HOMA-IR was explained by age, body fat %, VAT, RER:FQ and FH DM (adjusted R2=0.50, p<0.0001). Insulin-resistant women, and those with FH DM had a higher RER:FQ than their counterparts (p<0.01), independent of body fat % or distribution. CONCLUSION: In these apparently healthy, weight-stable women, insulin resistance and FH DM were associated with lower fat oxidation in relation to dietary fat intake, suggesting lower metabolic flexibility.
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    Injury risk assessment and the incidence of musculo-skeletal injuries in recreational long-distance runners over a 3-month training period
    (2017) Smith, Tanya; Kroff, Jacolene; Lambert, Estelle V
    Background: Long distance road running is continually growing as competitive and recreational sport, globally. Despite its popularity, a high burden of incidence of injury exists among runners. Previous research has focussed on specific injuries, whereas others have investigated isolated risk factors that may contribute to running related injuries. The purpose of the study is to determine possible internal and external screening variables that may predict the incidence of running-related injuries in general. Methods: Forty one recreational runners participated in an observational study over the course of 12 weeks. Screening assessments consisted of injury history, training history, and anthropometric measurements. Functional and performance assessments included the Foot Posture Index (FPI), the Functional Movement Screen (FMS), vertical jump, single leg hop and sit-and-reach tests. Participants were monitored over a period of 12 weeks by completing a weekly online logbook regarding their training and possible incidence of injury. Monitoring was terminated after 12 weeks of observation. Differences between injured and non-injured runners were determined using Independent -T-tests for mean differences, or Mann-Whitney U Test for distributional differences (non-parametric data). Binomial Logistic regression models were used to determine the influence of internal, external functional and external behavioural factors on the risk for running injury, respectively. Results: The total group revealed a cumulative incidence of injury of 63% over the 12 weeks of observation. There was no gender difference between incidences of injuries over the 12 week observation training period (OTP). Injured runners achieved a higher total FMS score (median = 16, Interquartile Range = 3) compared to uninjured runners (median = 15, Interquartile range = 3; p = 0.006). Binomial logistic regression models of external functional (FMS, Vertical Jump, Sit-and-Reach scores) factors [X² (3) = 9.764, p = 0.021] were statistically significant. Only the FMS score contributed significantly to the incidence of injury (p = 0.013) of the three external functional factors in the Regression Model. Discussion and Conclusion: The study adds to current evidence that the assessment of the Functional Movement Screen is important in predicting injury, however, the present study shows that a higher score obtained during the FMS increase your odds to sustain an injury. The study is in contrast with the body of evidence that the incidence of previous injury is the strongest predictor of the incidence of a current injury. The study concluded that the Functional Movement Screen is a useful screening tool to determine a long distance runner's risk for running-related injuries and should be included in health-injury risk assessments of recreational runners.
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    The comparison between subjective and objective free-living physical activity in women with diverse weight loss histories
    (2023) Burrows, Robyn Toni; Kroff, Jacolene
    Introduction: Weight regain following weight loss is a universal concern for successful obesity management strategies. The tendency evident in reduced-weight women to overestimate physical activity may be one of the causes of unsuccessful weight loss maintenance in the long term. The current study aimed to 1) identify differences in objective (accelerometry) and self-reported (GPAQ) free-living physical activity in women who experienced weight loss, and 2) determine whether overor-underestimation of physical activity was related to time at goal weight. Methods: Reduced-obese women (n = 19) were recruited for this study. The reduced-obese condition consisted of women who had lost a minimum of 10% of their body weight 18-6 months before testing. Prior to visiting the laboratory, participants were telephonically questioned to determine their inclusion or exclusion status for the study. During the first visit, participants completed physical assessments (BMI, body fat percentage), the Global Physical Activity Questionnaire (GPAQ), and underwent the accelerometer fitting. The accelerometer was worn for a period of 7 days and was used to measure free-living daily activity. Means ± SD were used to analyse parametric data and medians and interquartile range were used to assess non-parametric data. Pearson correlations were used to measure the association between the two methods. Paired sample t-tests, Chi-square tests and Effect sizes using Cohen's d were run. Finally, we visually inspected and statistically tested the results using Bland-Altman plots and simple liner regressions. Results: On average, participants lost 23.3  9.1 percent of their weight over an average period of 7  2.8 months. Participants underestimated their sedentary time and time spent in moderate-intensity activity and overestimated their vigorous-intensity activity. Bland-Altman plots revealed a proportional bias for time spent per day in sedentary time, vigorous-intensity activity, and MVPA. MVPA showed a statistically significant positive correlation between the two measures, r = 0.72, p = 0.0006. Time spent in moderate activity showed the best agreement between the self-reported measure and accelerometry, revealing no proportional bias (mean SD bias of -61.8 38.2 min per day). Chi-squared results revealed that 11 participants (of which 9 were at their goal weight for 6 months and 2 were at their goal weight for longer than 6 months) underestimated their MVPA. Chisquared results also revealed that 7 participants (of which 6 were at their goal weight for 6 months and 1 was at their goal weight for longer than 6 months) overestimated their vigorous-intensity activity. Discussion and conclusion: Underestimation of sedentary time and overestimation of vigorous intensity exercise put the group of reduced-obese women at risk for weight regain in the long term. The moderate-intensity activity was largely underreported, which requires further investigation. It is imperative that research on reduced-weight women make use of objective measures for the measurement of free-living activity, for self-reported measures will lead to a misinterpretation of this specific population's physical activity status.
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    The Effect of a 18-Week Supervised Exercise Program on Changes in Weight and Health Status in Overweight Individuals: The Healthy Weight Beginner and Intermediate Program
    (2022) Pholi, Kuda Nozibelo Grace; Kroff, Jacolene; Atterbury, Elizma
    Background: According to the South African National Health and Nutrition Examination Survey, approximately 69% of South African women and 29% of men are considered overweight/obese. In South Africa, overweight and obesity rates are on the rise and have reached epidemic proportions. Several conventional weight loss strategies have been employed and have been unsuccessful in addressing this issue. It is for this reason that this study strives to uncover if any improvement in weight and fitness status are associated with an improvement in health status. Methods: One of our main aims were to determine the success in weight loss and reduction in health risk factors in members who have completed 18-weeks of the Healthy weight programme. Therefore, this study is a retrospective, observational study of adults with a mean body mass index (BMI) of 32.63 ± 7.39 who completed an 18-week supervised exercise program. An online health questionnaire was completed followed by pre- intervention assessments which included: Anthropometric measures (height, weight, waist circumference, body fat percentage) followed by blood pressure, finger-prick random glucose and cholesterol measurements. A 12-min motion test to assess functional capacity were completed. All anthropometric, resting health measures and fitness tests were repeated at 12-weeks (post-beginner programme) and 18 weeks (post-intervention) after the start of the intervention. The intervention included 2 weekly classes with an optional gym class. The type of exercise intervention that was included in this study largely focused resistance training and cardiorespiratory fitness which targeted multiple large muscle groups. Each exercise session included 80 to 90 % exercise intensity as well as lumbopelvic core exercises. The data set was analysed as an intention to treat (ITT) protocol as some of the testing time points were missing. Results: Out of a possible 50 participants, 34 met the inclusion criteria of at least all 3 health measures taken on the 3 different occasions (baseline, post-beginner, postintervention). The 34 participants had a mean age of 47.26 ± 10.44 ranging between 24 years and 76 years old. 65 % of the participants were female. Anthropometric results showed significant changes in weight and waist circumference at 12- and at 18-weeks compared to baseline measures (p < 0.005). Additionally, body fat % significantly reduced at 12-weeks but increased slightly at 18 weeks diminishing the significant reduction compared to the baseline measure. In terms of fitness, participants succeeded in improving their average distance to complete a 12-min motion test by 14.5% (p < 0.001) at 12-weeks and 20% (p < 0.001) at 18-weeks compared to starting measures, respectively. After adjusting for multiple comparisons during post-hoc analysis, none of the health status outcomes (blood pressure, random glucose, random cholesterol) showed a significant improvement at any of the time points. In terms of associations, a change in body fat % could significantly explain some of the variance in the change (from baseline to 18-weeks) in cholesterol; and a change in weight could significantly explain some of the variance in the change in glucose over the same intervention time. Conclusion: The results of this study revealed the 18-week supervised exercise intervention led to a modest reduction (approximately 5%) in weight and a substantial improvement in fitness. However, no changes in health status were observed, suggesting that greater improvements in weight and fitness may be required to have a profound influence on health status.
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    The effect of working memory training on executive function in reduced-obese women: implications for long-term weight loss maintenance (the mind the gap 2 study)
    (2021) Rudner, Trinity; Kroff, Jacolene; Rauch, Laurie
    Background: Weight loss often results in various physiological and behavioural compensatory changes which increase susceptibility to weight regain, resulting in unsuccessful weight-loss maintenance in the long term. Evidence suggests that working memory (WM) plays a key role in self-regulation and executive control, which is vital in overcoming these compensatory responses to weight loss. The current study therefore aimed (1) to identify the compensatory responses that occur with weight loss, (2) to investigate whether WM training (WMT) can improve executive control in reduced-obese women, and (3) compare subjective and objective WM methodologies. Methods: Reduced-obese (n=23) and stable-weight (n=6) women were recruited in this study. All 29 women were characterised at baseline testing for various physiological, behavioural and cognitive outcomes. After baseline testing, a subset of 19 reduced-obese women underwent 6-weeks of WMT, after which they completed post-intervention testing and a 6-month follow up. The series of assessments at baseline and post intervention included: anthropometric measurements; eating and behaviour questionnaires; executive function and working memory tests; metabolic rate; blood profile (HbA1c; glucose; insulin); and appetite measures. Results: Reduced-obese women showed signs of greater eating disordered behaviour and greater post-prandial energy efficiency compared to stable-weight women, although there appeared to be no difference in their executive function. The WMT appeared to result in improved WM capacity in reduced-obese women, which was retained in the long term, and there was some evidence of transfer to behaviour, with an observed reduction in eating-disordered behaviour. When comparing WM methodologies there appeared to be a contradictory relationship between subjective and objective WM measures. Conclusions: The results from this study support the evidence that physiological and behavioural changes occur in those that have lost a significant amount of weight, stressing the importance of finding weight-loss therapies that target these compensatory responses to weight loss. WMT was found to improve WM capacity in reduced-obese women, however, study limitations mean that the effects the training may have had on behaviour and weight maintenance could not be accurately determined. Furthermore, the contradictory relationship found between subjective and objective measures of WM add to the uncertainty that they measure the same underlying construct, which highlights the importance of utilising various types of measures in the analysis of WM and executive function.
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    The role of metabolic rate and substrate utilization in the maintenance of body weight, body composition and insulin sensitivity
    (2019) Clamp, Louise Diana; Kroff, Jacolene; Goedecke, Julia
    Obesity treatment requires approaches that target the reduction of body weight and fat mass. The improvement of cardiorespiratory fitness (CRF), metabolic flexibility and insulin sensitivity also contribute towards reducing obesity-associated risk factors. While energy restriction alone results in significant weight loss, exercise-only interventions provide small amounts of weight loss and prevent weight gain, while also improving many of the other variables targeted in obesity treatment. Once achieved however, successful weight-loss maintenance is challenging, with many individuals subsequently experiencing weight regain. The main objectives of this thesis were to explore the role of metabolic rate and substrate utilization in influencing body weight, body composition and insulin sensitivity. This twopart thesis hypothesised that: 1) exercise training, without dietary intervention, will improve metabolic rate and substrate utilization in a sedentary obese population, and that this would be associated with improved body composition, insulin sensitivity and CRF; and 2) metabolic rate, substrate utilization and insulin sensitivity are altered through weight loss/regain, predisposing these individuals to weight regain and impairing successful weight-loss maintenance. In Part 1 of this thesis a 12 week exercise intervention in sedentary, obese (BMI 30-40kg.m-2 ) black South African (SA) women (aged 22, IQR 21-24 years) was completed. Previous studies have shown that black SA women present with very low CRF, a key indicator of increased risk for non-communicable disease (NCD), and have a high prevalence of obesity and insulin resistance (IR). They are thus at increased risk for developing type 2 diabetes (T2DM). Furthermore, physiologically black SA women have also been shown to have less visceral adipose tissue (VAT) and more peripheral gluteal fat mass (FM) compared to their white counterparts, but are paradoxically more IR. Despite this presentation, to date there has been no supervised exercise intervention studies undertaken in this very high risk population group. The first study of this thesis (chapter 2) aimed to assess the effects of the exercise intervention on changes in CRF, energy expenditure (EE) and substrate utilization, both at rest and during steady-state exercise compared to non-exercising controls. It also assessed baseline and changes in these measurements in relation to changes in body composition. Black SA women (BMI 30-40 kg.m-2 , 20-35 y) were recruited and randomized into control (CTL, n=15), or exercise (EXE, n=20) groups. The CTL was instructed to maintain usual activity while the EXE completed 12 weeks of combined resistance and aerobic exercise training (4d.wk-1 , 40-60min.d-1 @ >70% peak heart rate (HRpeak)). At pre-intervention, a treadmill-based CRF test, measuring peak volume of oxygen consumption (VO2peak), was carried out. Thereafter resting and steady state exercise (50% VO2peak) energy expenditure (EE) and respiratory exchange (RER) were measured along with body composition (dualenergy X-ray absorptiometry (DXA)). A frequently sampled intravenous glucose tolerance test (FSIGT) was also carried out to determine changes in insulin sensitivity. These tests were repeated at post-intervention testing with steady state testing being carried out both at the same relative intensity (50% post-testing VO2peak) and the same workload (treadmill speed and gradient) as used for pre-testing. Dietary intake (4d diary) and daily step-count (ActivPAL) data was collected at pre-testing, 4, 8 & 12 weeks. Results showed that all participants had very low baseline CRF, falling below the 20th percentile previously shown in African American women. In response to exercise training, CRF increased by ≈11% and rates of fat oxidation during steady-state exercise were improved, while in controls these remained unchanged. Compared to CTL, EXE also showed small but significant reductions, in weight, as well as BMI, waist (WC) and hip (HC) circumferences. In contrast weight, BMI and WC increased in non-exercising controls. Gynoid FM (absolute FM and as a proportion of total FM), rather than visceral adipose tissue (VAT), was reduced in exercise participants. Within the exercise group higher baseline fat oxidation rates during steady state exercise and lower resting carbohydrate oxidation rates explained 61.6% (p< 0.001) of the variability in changes in gynoid FM in response to 12 weeks of exercise training in this group. In conclusion, exercise training improved CRF and fat oxidation rates during submaximal exercise in sedentary, obese black SA women. Higher fat oxidation rates during steady state exercise and lower resting carbohydrate oxidation rates at baseline were associated with the mobilization of gynoid FM in response to exercise training, rather than VAT as is typically shown in exercise interventions. This novel finding potentially represents an ethnic/gender specific response to exercise training. Further studies are needed to confirm this. Similar exercise training programs, that are sustainable over the long term, would therefore be beneficial in achieving meaningful increases in CRF while also supporting weight management and body composition improvements in this high risk population group. Using data from the exercise intervention in obese black SA women, the second study of this thesis (chapter 3) investigated inter-individual variability in the CRF response (∆VO2peak) to exercise training. The study specifically aimed to compare changes in EE and substrate utilization at rest and during steady state exercise, body weight and composition and insulin sensitivity between high and low CRF responders to the 12 week intervention. Furthermore it aimed to explore associations between baseline metabolic rate, EE and substrate utilization and subsequent changes in CRF in response to exercise training, to determine if baseline variability in these measures contributed to inter-individual variability in the CRF outcome. Within the exercise group, high inter-individual variability in CRF response to exercise training was identified. Based on a median split in ∆VO2peak, high responders (HRS, n=10) increased CRF by 21.7 ±10.0% (p< 0.001) compared to no change in both low responders (LRS, n=10; +0.6 ±6.3%, p=0.748) and CTL (-3.2 ±10.8%, p=0.195). This occurred despite all groups having similar baseline VO2peak and the exercise group receiving the same exercise dose (number of exercise sessions attended and average intensity of the exercise sessions). At baseline, HRS derived ≈62% of energy expenditure from fat oxidation during steady-state exercise compared to just 41% in LRS, who relied to a greater extent on carbohydrate oxidation. Furthermore, HRS were ≈11 kg lighter than LRS. There was also a positive association between BMI and RER such that individuals with higher BMI showed lower fat utilization (i.e., higher RER). HRS reduced gynoid FM whereas in LRS this remained unchanged. This is in line with the findings of the previous chapter which showed that exercise-related reduction in gynoid FM was associated with greater baseline fat oxidation. LRS showed improvements in insulin sensitivity compared to CTL and HRS. Using regression analysis including the exercising participants, greater baseline carbohydrate oxidation rates both at rest and during steady state exercise predicted a poorer CRF to exercise training, explaining 37.5% of the variability in ∆VO2peak. To the best of my knowledge, this is the first study to show that baseline variability in substrate utilization among sedentary obese individuals contributes towards explaining the variability in the CRF response to exercise training. However, further studies are required to confirm these results. Together, these studies show that higher fat oxidation rates are necessary for FM mobilization, while correspondingly reduced reliance on carbohydrate oxidation both at rest and during exercise supports improvements in CRF in response to exercise training. These findings add to a growing body of research aimed at explaining inter-individual variability in exercise intervention outcomes and may contribute to individualizing the exercise prescription. Part 2 of this thesis used a cross-sectional approach and investigated firstly whether there was evidence for metabolic adaptation to weight loss/regain in response to long term weight maintenance, potentially predisposing individuals to future weight gain/regain. Secondly, I investigated whether insulin sensitivity is altered as a result of prior weight loss history, or whether successful weight loss restores insulin sensitivity to levels that are comparable to phenotypically similar controls with no weight loss history. Weight stable, BMI-matched South African women aged 20-45 years with or without a history of prior weight loss were screened and recruited. Four groups were defined as follows: Weight Reduced (RED, n=15) - lost at least 15% of body weight & maintained a reduced weight (BMI ≤ 27kg.m-2 ) for over 12 months (15% of body weight), but relapsed back to overweight or obese (BMI ≤ 27kg.m-2 ); and overweight or obese (BMI ≤ 27kg.m-2 ) stable-weight controls (OSW, n=11) - no history of significant weight loss. The first study in Part 2 (Chapter 4) compared metabolic rate and substrate utilization in RED and REL to their respective BMI-matched controls with no weight loss history, both at rest and in response to a high fat meal challenge. Metabolic rate and substrate utilization were measured both at rest, immediately after consumption of the high fat test-meal and every hour thereafter for three hours. Dietary intake (3 x 24h recalls) and physical activity (ACTi Graph GT3X accelerometer worn for 7 days) data was collected and body composition was measured (bioelectrical impedance, BIA). Questionnaires were also completed covering weight history, socio-economic status and eating behaviour. Results showed that there was no difference in either resting EE or substrate utilization between the RED and REL compared to the respective BMI-matched controls, after accounting for fat free mass (FFM). The TEF, postprandial EE (absolute and per kg FFM), post-prandial energy balance, RER, fat oxidation rate and post-prandial fat balance were similar between RED and REL compared to their respective controls, indicating that there was no evidence of metabolic adaption to weight loss. However, successful weight-loss maintainers did show behavioural strategies that may have counteracted weight-loss associated adaptive thermogenesis and supported weight-loss maintenance. These individuals had manipulated macronutrient intake (increasing protein and reducing carbohydrate intake), were more physically active, exhibiting less sedentary behaviour and increased moderate and vigorous activity, and had greater fat free soft tissue mass (FFSTM). While the presence of adaptive thermogenesis is not disputed in these results, the distinct physiological and behavioural differences together observed in the RED may have been instrumental in attenuating weight-loss associated declines in EE, shown to persist into weight-loss maintenance. Together with these lifestyle strategies, weight reduced individuals also reported greater dietary restraint in comparison to controls. This is surprising after such a significant period of weight-loss maintenance (median weight-loss maintenance: 30 months) and highlights the ongoing challenges to maintain reduced weight. These findings contribute to the relatively smaller body of research into the longer-term persistence of weight-loss associated adaptive responses in comparison to that covering the acute weight loss phase. It also highlights strategies that may be effective in counteracting metabolic adaption to weight loss. As such, these strategies may warrant inclusion as part of weight-loss maintenance programs as they potentially help to reduce the risk for weight regain as a result of weight-loss associated adaptive thermogenesis. The next study in Part 2 of the thesis (Chapter 5) aimed to examine the impact of successfully maintained weight loss and weight-loss relapse on insulin sensitivity compared to BMImatched controls without a weight loss history. Predictors of variability in insulin sensitivity were also explored. Following the measurement of resting metabolic rate and substrate utilization a 75g oral glucose tolerance test was used to determine fasting and 2hr plasma glucose and insulin. The Homeostatic Model Assessment (HOMA-IR) and insulin sensitivity index (ISI(0,120)) were used to assess insulin sensitivity. A novel finding of this study was that successfully maintained, weight-reduced individuals displayed enhanced measures of insulin sensitivity (lower HOMA-IR and higher ISI(0,120) measurements), compared to all other groups, including BMI-matched controls with no weight loss history. Previously studies have investigated changes in insulin sensitivity in response to weight loss and in weight-loss maintenance, but not necessarily in comparison to individuals without a weight loss history as defined by this study protocol. With weight regain however, insulin sensitivity measures for REL were not different compared to either LSW or OSW, showing that enhanced insulin sensitivity accompanying weight loss is likely reversed with weight regain. Prior weight history, fasting substrate utilization, measures of body weight and composition, protein intake per kilogram, physical activity and CRF were all associated with measures of insulin sensitivity. Using these variables in regression models, ≈60% of the variability in insulin sensitivity in both HOMA-IR and ISI(0,120). Weight loss and weight regain history followed by fasting RER were the most significant independent predictors of insulin sensitivity. In conclusion, a novel finding was that successfully weight-reduced individuals are more insulin sensitive than their BMI-matched controls with no weight loss history, independent of dietary intake and physical activity. This remains evident even after significant periods of maintaining the reduced weight. Weight loss maintenance programs are essential to retaining metabolic benefits acquired through weight loss. Remaining physically active by reducing sedentary behaviour and in particular including small amounts of vigorous physical activity significantly predicts improved insulin sensitivity. This thesis includes a number of novel findings. In Part 1, we showed that in response to exercise training gynoid FM, rather than VAT, was reduced in sedentary obese black SA women undergoing a 12 week exercise intervention, which may represent an important ethnic/gender specific response. We also showed that substrate utilization plays an important role in altering body composition and CRF in response to an exercise intervention. Greater fat oxidative capacity at the outset resulted in an enhanced ability to reduce gynoid FM in response to exercise training. Furthermore, a greater reliance on carbohydrate rather than fat oxidation during baseline testing predicted a poorer CRF response. Identification of individuals with a lower capacity for fat oxidation at the outset of an exercise intervention may therefore allow for a more targeted exercise prescription, which may in turn improve outcomes of exercise interventions. The lack of clinically significant weight loss suggests that future exercise interventions should prescribe exercise EE of sufficient magnitude to achieve weight loss and emphasize adherence to this prescription or include some dietary restriction. Education around the possible adaptive responses to increased EE and the imposed energy deficit, highlighting the strategies employed by weight reduced individuals from Part 2 of this thesis, may help to attenuate potential metabolic adaption to increased EE and further improve the weight loss outcomes of exercise-only interventions. It may also help to inform weight-loss maintenance programs to assist individuals to maintain the reduced weight following weight loss. The enhanced insulin sensitivity in weight reduced individuals as shown in Part 2, may potentially represent an ongoing and persistent adaptive response to weight loss that may in itself increase the risk for weight-loss relapse. Education around the physiological adaption to significant weight loss and emphasizing strategies that may counteract this metabolic adaptation may improve the efficacy of both weight-loss and weight-loss maintenance programs.