RESUMEN
BACKGROUND: Establishing profiles of physical activity (PA) is critical in tackling the chronic diseases associated with lack of PA and avoiding healthcare costs. OBJECTIVE: To investigate PA levels in urban-based South African (SA) primary school learners. METHODS: The Physical Activity Questionnaire for Older Children was completed by 7 348 learners (3 867 males and 3 481 females) aged 8 - 14 years, of whom 49% were white, 39% black and 12% from other ethnic groups. Differences in PA levels by ethnic origin and province were determined using an analysis of covariance after adjusting for gender (p<0.05). Bonferroni corrections controlled for multiple comparisons. A fitted regression model examined age-related differences in PA adjusting for province. RESULTS: Of SA learners aged 8 - 14 years, 57% (n=4 224) engaged in moderate levels of PA. Thirty-one percent (n=2 247) did not meet internationally recommended amounts of moderate to vigorous physical activity. Overall, males reported higher PA levels than females (p<0.0001). PA levels declined with age from 11 to 14 years by 14% and 20% in males and females, respectively. Black learners had higher PA levels than white learners (p=0.0039). There were also significant differences in PA levels between the provinces (p<0.0001). CONCLUSION: This study provides evidence of differences in PA levels between gender, age and ethnic groups, and between provinces. A targeted approach to increase PA in high-risk populations in SA is warranted. Increased PA will help reduce the risk of chronic diseases and will contribute to the health of SA's population and the growth of the country's economy.
RESUMEN
Dose-response relationships between exercise training volume and blood lipid changes suggest that exercise can favourably alter blood lipids at low training volumes, although the effects may not be observable until certain exercise thresholds are met. The thresholds established from cross-sectional literature occur at training volumes of 24 to 32 km (15 to 20 miles) per week of brisk walking or jogging and elicit between 1200 to 2200 kcal/wk. This range of weekly energy expenditure is associated with 2 to 3 mg/dl increases in high-density lipoprotein-cholesterol (HDL-C) and triglyceride (TG) reductions of 8 to 20 mg/dl. Evidence from cross-sectional studies indicates that greater changes in HDL-C levels can be expected with additional increases in exercise training volume. HDL-C and TG changes are often observed after training regimens requiring energy expenditures similar to those characterised from cross-sectional data. Training programmes that elicit 1200 to 2200 kcal/wk in exercise are often effective at elevating HDL-C levels from 2 to 8 mg/dl, and lowering TG levels by 5 to 38 mg/dl. Exercise training seldom alters total cholesterol (TC) and low-density lipoprotein-cholesterol (LDL-C). However, this range of weekly exercise energy expenditure is also associated with TC and LDL-C reductions when they are reported. The frequency and extent to which most of these lipid changes are reported are similar in both genders, with the exception of TG. Thus, for most individuals, the positive effects of regular exercise are exerted on blood lipids at low training volumes and accrue so that noticeable differences frequently occur with weekly energy expenditures of 1200 to 2200 kcal/wk. It appears that weekly exercise caloric expenditures that meet or exceed the higher end of this range are more likely to produce the desired lipid changes. This amount of physical activity, performed at moderate intensities, is reasonable and attainable for most individuals and is within the American College of Sports Medicine's currently recommended range for healthy adults.
