Studies investigating the relationship between physical activity and mental health are mostly limited to adults. In adults, physical activity has been shown to have a short term mood-enhancing effect.
Moderate levels of intensity and duration of physical activity have been shown to have a stress-reducing effect, but an additional increase of either the duration or the intensity will not have further beneficial effects. For children and adolescents, it is assumed that physical activity is associated with good mental health, especially in relation to self-esteem, self-efficacy, greater perceived physical competence, greater perceived health and well-being, but there is almost no evidence that the amount of physical activity is related to better social and moral development or to psychological variables such as body image, academic functioning, social skills, anxiety, hostility and aggression.
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Diabetes mellitus is a disorder of the carbohydrate metabolism characterized by high blood sugar levels. It is known to be an important CVD risk factor and it is often accompanied by overweight or obesity.
Diabetes mellitus develops when there is inadequate production of insulin by the pancreas, or inadequate utilization of insulin by the cells. Clinically, two major forms are distinguished: type 1 diabetes, also known as juvenile onset diabetes, and type 2 diabetes, also known as adult onset diabetes.
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In adults it is known that endurance training can reduce both systolic and diastolic blood pressure by approximately 10 mmHg in individuals with moderate essential hypertension, but exercise does not seem to have an effect on subjects with severe hypertension.
However, the mechanisms responsible for the decrease in blood pressure with physical activity have yet to be determined. A reduced cardiac output is mentioned as a reason for the fact that activity lowers blood pressure, although this cardiac output reducing effect of physical activity is not found in all studies. If there is no influence on cardiac output, then the blood pressure decreasing effect may be caused by a reduction in peripheral vascular resistance, which may be due to a reduction of sympathetic nervous system activity.
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It is known that lipoprotein levels are directly related to the process of atherosclerosis and therefore to the occurrence of CVD. Although total serum cholesterol has been found to be related to CVD, its atherogenic effect depends on the structure of the cholesterol or, in other words, on the ratio between low-density lipoprotein cholesterol (LDL) and high-density lipoprotein cholesterol (HDL).
It is assumed that LDL may act directly or indirectly to cause endothelial damage, with subsequent proliferation of arterial smooth muscle cells resulting in an accumulation of lipids and a progression to atherosclerotic plaque formation. HDL, on the other hand, is assumed to be protective against CVD; HDL seems to be responsible for carrying cholesterol from peripheral tissue, including the arterial walls, back to the liver where it is metabolized and excreted.
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One of the problems in assessing the prevalence of physical inactivity (and therefore the estimation of the PAR) is that it is difficult to define physical inactivity. Most of the time, physical inactivity is defined as ‘not reaching the guidelines for healthy physical activity’.
However in the beginning of the 1990s, Cale & Almond (1992) reviewed 15 studies conducted on British children and reported that children seldom participate in activity at a level that would have a cardiovascular training effect or a health benefit.
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