Identification and modification of cardiometabolic disease risk factors in South African urban primary school children
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Date
2018
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Publisher
University of Zululand
Abstract
The initial asymptomatic process of atherosclerosis is known to develop in
childhood and is associated with increases in cardiometabolic disease (CMD) risk
factors. Low physical activity (PA) levels and sedentary lifestyles have been identified
as contributory factors to CMD. In addition, PA levels are known to influence the
function of the cardiac autonomic nervous system (ANS), and are a possible
mechanism for explaining the association between insufficient PA, morbidity and
mortality. Consequently, it has been proposed that sufficient PA may enhance cardiac
ANS activity in children. However, there is still a lack of consensus on the exact dosage
of exercise required for optimal ANS adaptation.
This thesis aims to identify and modify the risk for CMD in urban primary school
children. A cross-sectional study was performed to establish PA levels in South African
primary school children. This was followed by a study that examined associations
between individual CMD risk factors and altered ANS activity. The effect of two different
exercise doses on CMD risk factors in overweight children was explored in a pilot study
that lead to the quasi experimental study where the effectiveness of isocaloric exercise
protocols on CMD risk factors and cardiac autonomic modulation in children were
explored. Exercise interventions were set at either 65% to 70% of the maximum heart
rate (MHR) in the moderate-intensity continuous training (MICT = 29) group or >80%
MHR in the high-intensity interval training (HIIT = 29) group, or the interventions were
combined in the alternate (ALT = 27) group. Heart rate variability (HRV) was used to
measure cardiac ANS activity.
Overall, we found significant discrepancies in PA levels among gender, age and
ethnic groups, raising important questions about population group equality in terms of
access to participate in PA. The second cross-sectional study established strong
associations between individual CMD risk factors and cardiac ANS activity. Lastly, the
pilot study showed different cardiometabolic effects induced by moderate-intensity and
vigorous-intensity. While the quasi experimental study demonstrated that both the
magnitude and components of CMD risk factors and ANS relate to exercise intensity.
When the effects of these interventions were examined, enhanced vagal activity
(RMSSD, pNN50, SD1) seemed to be achieved through high-intensity interval training
(HIIT), when compared with moderate-intensity continuous training (MICT). In
conclusion, this thesis provides evidence that HIIT induces more superior
cardioprotective effects in children than does MICT. The favourable outcomes of HIIT
may have important clinical implications in regards to reducing the risk of developing
CMD; however, studies that implement longer terms are required to confirm the
findings.
Description
Thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy in Human Movement Science (Kinderkinetics)in the Faculty of Science and Agriculture at the University of Zululand, 2018.
Keywords
cardiometabolic disease, cardiac autonomic nervous system (ANS), CMD