Physical inactivity causes obesity, a condition which is related to insulin resistance, hypertension, diabetes mellitus, dyslipidemia and the metabolic syndrome (MS). MS is the collective description of lifestyle diseases associated with significant morbidity and premature mortality. MS has recently been observed in youth, and if left untreated could lead to cardiovascular diseases. Regular physical activity (PA) and exercise training appear to modify the independent risk factors for MS and cardiovascular diseases, and has a positive effect on waist circumference, blood pressure, body fat percentage, insulin sensitivity and arterial compliance.
The aim of this study was to determine the relationship between body composition and selective markers of the MS, and the extent to which a PA intervention programme will influence selective markers of the MS, body composition and markers of vascular function in black adolescents.
Grade 9 classes from two high schools, in a low socio-economic status area near Potchefstroom, participated as the experimental and control group respectively. The experimental group consisted of 194 participants and the control group of 57 participants. The experimental group participated in a 10-week P A intervention. Body mass index, stature, body mass, waist-hip ratio, waist circumference, hip circumference, body fat percentage, fasting serum insulin, fasting plasma glucose, plasma leptin, homeostasis model assessment of insulin resistance (HOMA-IR), systolic blood pressure (SBP), diastolic blood pressure (DBP), Windkessel arterial compliance (Cw), total peripheral resistance, Tannerstage and habitual physical activity were measured.
The data were analysed by means of descriptive statistics, Mann-Whitney U-tests, analysis of covariance (ANCOVA), Pearson's correlation analyses and multiple regression models. HOMA-IR and leptin were log transformed before analyses because of the skewed distribution. The Statistica for Windows and SAS computer programmes were used to analyse the data according to the above-mentioned aims of the study.
Results and conclusions
Firstly, a significant positive association was found between body fat percentage and both SBP (p=O.02) and HOMA-IR (p=O.02) respectively. Girls with a high body fat percentage had higher SBP (p=O.004), DBP (p=O.03), plasma insulin (p=O.004) and HOMA-IR (p=O.004) than girls with normal body fat percentage. Secondly, a 10-week PA intervention led to a significant decrease in SBP (p=O.000061), a trend of decreasing HOMA-IR, and a trend of increasing Cw in black adolescents. Lastly, no significant differences were found in body composition and vascular function variables for the normal-and over-fat group in this study after the 10-week PA intervention.
In conclusion, the results of this study showed firstly, that there was a positive association between body fat percentage and SBP and HOMA-IR respectively; and secondly, that PA had a positive effect on some MS markers, namely: SBP and HOMA-IR. Further research regarding PA intervention's influence on the MS in black adolescents should be conducted, as there is clearly a shortage of literature that focuses on this research theme within this South African ethnic group.||