Browsing by Author "Mendham, Amy"

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    The effect of a 12-week exercise training intervention on physical behaviour patterns and perceptions of body image in Black South African women living with overweight and obesity
    (2025) Phiri, Lindokuhle; Goedecke, Julia; Mendham, Amy; September, Alison
    Background: This thesis aimed to evaluate the effects of a 12-week combined (aerobic and resistance) exercise training intervention on: i) the changes in physical behaviours and ii) body image and self-efficacy. Lastly, iii) this thesis explored the perceptions and experiences of the women after participating in the 12-week combined exercise training intervention. Methods: Forty-five young (18-35 years) apparently healthy Black SA women living with overweight and obesity were randomised into either an exercise (EXE; n=23) or a control group (CON; n=22). The EXE group participated in 12-week aerobic and resistance supervised exercise training (40-60 min/session, 4 days/week), while the control group maintain their usual physical behaviour patterns. Generalized self-efficacy (GSE) questionnaire and Stunkard's silhouettes were used to measure general self-efficacy and perceptions of body image. Participants wore ActiGraph and ActivPAL accelerometers simultaneously for 7 days to quantify physical activity (PA) and sedentary behaviour (SB) at baseline, week 4, 8 and 12, considering all days, exercise days and non-exercise days. Focus group discussions (FGDs) and in-depth interviews (IDIs) were conducted to investigate the participants' perceptions and experiences of the intervention. Results: Thirty-five participants, EXE (n=20) and CON (n=15) completed the intervention. There was a group x time interaction for body weight and CRF, whereby weight decreased by ~1 kg (p= 0.007) and cardiorespiratory fitness (CRF) increased by ~2.7 ml/kg/min (p=0.001) in the EXE group only. Considering only exercise days, moderate-to- vigorous physical activity and total physical activity (%) increased from baseline to weeks 4, 8 and 12 in the EXE group, but did not change in the CON group (p<0.001 for group x time interaction). Daily steps accumulated during the exercise days increased from baseline, (mean ± standard deviation; 9429 ± 4019 steps/day) to week 4 (15050 ± 3167 steps/day; p<0.001), week 8 (14780 ± 4224 steps/day; p<0.001) and week 12 (15695 ± 3550 steps/day; p<0.001), but did not change in the CON group (10131 ± 4561 steps/day). There was a significant decrease in SB (% of awake time) from baseline to week 12 (58.9 ± 9.4% to 48.9 ± 9.1%; p<0.001 for group x time interaction) among the EXE group considering exercise days only. Despite the average measured body mass index of 33.8 ± 2.7 kg/m2 for both groups at baseline, 31.4% of the women classified themselves as normal weight, 65.7% as overweight and only 2.9% as living with obesity. None of the women perceived themselves as living with obesity after the intervention. The Stunkard's silhouettes showed that women from both groups presented with body size discordance, such that at baseline, most participants desired a smaller body size and this did not change in response to the intervention. A significant decline in general self-efficacy was observed in both groups post intervention (p=0.021, time effect), and this did not differ between groups (p=0.801, for group x time interaction). Qualitative findings showed that weight loss (anticipated and actual) and financial remuneration for travelling costs and time (nominal) were reported as motivators for enrolling and staying in the intervention. Improvement in psychological wellbeing (improved mood and self-esteem) and perceived level of self-efficacy were other reported benefits of the intervention. Lack of time, distance to the training venue and limited transport to the training venue were some of the barriers to attending the exercise sessions. Conclusion: To the best of our knowledge, this is the first study in SA to show significant increases in TPA and MVPA, with compensatory reduction in SB in response to combined exercise training among women living with overweight and obesity. A clear indication that the overall changes in the physical behaviour patterns among the exercise group were largely due to the participation in the exercise sessions. Furthermore, the positive changes in physical behaviour patterns and CRF experienced by the exercise group have the potential to improve the cardiometabolic health of this population. In addition, findings from this thesis show promise of the positive impact of exercise on improving psychological wellbeing. Lastly, majority of the women in the study desired to be smaller in body size, suggesting that these women may be receptive to health and weight-loss exercise interventions.
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    The effect of an exercise intervention on insulin sensitivity, insulin secretion and insulin clearance in black obese South African women
    (2020) Fortuin-De Smidt, Melony; Goedecke, Julia; Mendham, Amy
    Introduction: Black African populations present with low insulin sensitivity (SI) and hyperinsulinemia, the latter due to high insulin secretion and reduced clearance. In addition, they exhibit lower levels of central and ectopic fat, compared to their white counterparts, contradicting the known correlates of SI typically reported in white populations. Moreover, in black African women hyperinsulinemia is in excess of the level needed to compensate for low SI, with a corresponding high disposition index (DI), a marker of insulin response that accounts for the level of SI. Further, obese, black African women have a high risk for type 2 diabetes (T2D), but the correlates of hyperinsulinemia have not been fully elucidated, especially the role of ectopic fat and body fat distribution. Exercise training is beneficial to improve SI and DI, however, whether these effects are mediated by changes in ectopic fat in skeletal muscle, liver and pancreatic depots is unknown. Accordingly, exercise training can be used as a model to assess the correlates of hyperinsulinemia and SI in cohorts at high risk for developing T2D, such as obese black African women. This thesis therefore aims to describe the correlates of hyperinsulinemia and SI and to evaluate the effect of exercise training on these components with emphasis on the role of body fat distribution and ectopic fat in mediating these changes. Methods: Firstly, a cross-sectional analysis of 45 obese (BMI 30-40 kg/m2 ) black South African women (age 20-35 years) without T2D was conducted. Thereafter the women were block randomized into an exercise training (n=23) or no exercise (control, n=22) group. The exercise training group participated in a 12-week combined aerobic and resistance training programme (40-60 min session, 4 days/week) supervised by a biokineticist. Pre and post-intervention testing included assessment of acute insulin response to glucose (AIRg), SI, DI (AIRg x SI), insulin secretion rate (ISR), hepatic insulin extraction (HIE) and peripheral insulin clearance (CLp) (frequently sampled intravenous glucose tolerance test); body fat mass and regional adiposity (dual-energy X-ray absorptiometry); hepatic, pancreatic and skeletal muscle fat and abdominal subcutaneous (aSAT) and visceral adipose tissue (VAT) (magnetic resonance imaging); intramyocellular (IMCL) and extramyocellular fat content (EMCL) (magnetic resonance spectroscopy). Results: The baseline results showed that a high DI was associated with low VAT (r0.565, p< 0.001), pancreatic fat, soleus IMCL and EMCL with VAT explaining most of the variance in DI (32%). SI was inversely associated with VAT (rho -0.417, p=0.007) and AIRg was inversely and HIE was positively associated with VAT-aSAT ratio (rho - 0.345, p=0.029 and rho 0.510, p=0.011, respectively). DI was positively associated with CLp (rho 0.528, p=0.006), while its components (SI and AIRg) were not. Results from the intervention showed that exercise training increased DI (median (interquartile range): 6.1 (3.6-7.1) to 6.5 (5.6-9.2) x103 arbitrary units, p=0.028), SI (2.0 (1.2-2.8) to 2.2 (1.5-3.7) (mU/l) -1 min -1 , p=0.005) and VO2peak (mean ± standard deviation: 24.9±2.42 to 27.6±3.39 ml/kg/min, p< 0.001), with no changes in control group. Exercise training decreased body weight (84.1±8.7 to 83.3±.9.7 kg, p=0.038) and gynoid fat mass (18.5±1.7 to 18.2±1.6%, p< 0.001). AIRg, ISR, HIE, CLp, aSAT, VAT and ectopic fat were unchanged after exercise training. However, the control group increased body weight and aSAT. The increase in SI and DI were not associated with changes in body composition, body fat distribution or ectopic fat. Conclusion: Novel results from our cross-sectional analysis showed that, in obese black South African women, DI was positively associated with peripheral insulin clearance, probably due to higher SI of peripheral tissue. Moreover, the most important correlate of a high DI was low VAT independent of ectopic fat accumulation in other sites. Further, we showed that low AIRg and high HIE correlated with a high VAT-aSAT ratio, while low SI was associated with high VAT. These associations require further exploration to determine direction of causality. Findings from our exercise intervention study extend on previous research by showing that moderate-to-high intensity combined aerobic and resistance exercise training increased SI and improved cardiovascular fitness, but insulin secretion, hepatic insulin clearance, ectopic and central fat depots did not change. Our results suggest that hyperinsulinemia may not occur solely as a compensatory mechanism for low SI and that ectopic and central fat might not be the primary correlates of insulin resistance in this cohort. Rather, intrinsic factors within muscle and adipose tissue may be putative mediators for observed improvements in the metabolic outcomes but will require further elucidation. Further research is required to confirm the causal role of VAT on low DI and to determine whether a long-term exercise training program and/or a low carbohydrate/glycemic index diet will reduce AIRg in those with hyperinsulinemia.